SUDOERS(5)
💅 SUDOERS(5) — File Formats Manual
okay bestie, so this is SUDOERS(5), the manual page for the sudoers plugin. Buckle up, it's a long one but we're gonna get through it together 🫶
✨ NAME ✨
sudoers — the default sudo security policy plugin, periodt 👑
🦋 DESCRIPTION 🦋
So like, the sudoers policy plugin is the thing that decides what sudo privileges a user gets. It's the default sudo policy plugin, fr fr. The policy is driven by the /etc/sudoers file or, optionally, in LDAP. The whole policy format is described in detail down in the “SUDOERS FILE FORMAT” section, and if you wanna know about storing sudoers policy info in LDAP, go check out sudoers.ldap(5).
🎀 Configuring sudo.conf for sudoers 🎀
sudo checks the sudo.conf(5) file to figure out which plugins to load. If there's no sudo.conf(5) file at all, or if it doesn't contain any Plugin lines, then sudoers gets used for auditing, policy decisions and I/O logging. If you wanna explicitly tell sudo.conf(5) to use the sudoers plugin, this is the config you'd use:
Plugin sudoers_audit sudoers.so
Plugin sudoers_policy sudoers.so
Plugin sudoers_io sudoers.soStarting with sudo 1.8.5, you can pass optional arguments to the sudoers plugin in the sudo.conf(5) file. Those plugin arguments, if there are any, go after the path to the plugin (like, after sudoers.so). Only the plugin that opens (and parses) the sudoers file is actually affected by them, iykyk.
For sudo version 1.9.1 and higher, that plugin is sudoers_audit. For older versions, it's sudoers_policy. You can pass multiple arguments separated by white space. For example:
Plugin sudoers_audit sudoers.so sudoers_mode=0400 error_recovery=falseThese are the plugin arguments that are supported:
error_recovery=bool— controls whether sudoers should try to recover from syntax errors in the sudoers file. If it's set totrue(which is the default), sudoers tries to recover from a syntax error by throwing away the part of the line containing the error, all the way to the end of the line. A value offalsedisables error recovery. Before version 1.9.3, no error recovery happened at all.ignore_perms=bool— lets you disable the security checks when loading the sudoers file. If it's enabled, the sudoers file gets loaded no matter what the owner or file mode is. This one is intended for testing purposes and should not be enabled on production systems, no cap 🙈.ldap_conf=pathname— overrides the default path to theldap.conffile.ldap_secret=pathname— overrides the default path to theldap.secretfile.sudoers_file=pathname— overrides the default path to the sudoers file.sudoers_uid=user-ID— overrides the default owner of the sudoers file. Specify it as a numeric user-ID.sudoers_gid=group-ID— overrides the default group of the sudoers file. It must be specified as a numeric group-ID (not a group name!).sudoers_mode=mode— overrides the default file mode for the sudoers file. Specify it as an octal value.
For more deets on configuring sudo.conf(5), just go read its manual, bestie.
🔐 User Authentication 🔐
The sudoers security policy requires that most users authenticate themselves before they can use sudo. No password is needed if the invoking user is root, if the target user is the same as the invoking user, or if the policy has disabled authentication for that user or command.
Unlike su(1), when sudoers requires authentication it validates the invoking user's credentials, not the target user's (or root's) credentials. You can change that with the rootpw, targetpw and runaspw flags, which we'll get to later 💅.
If a user who isn't even listed in the policy tries to run a command via sudo, mail gets sent to the proper authorities. The address used for that mail is configurable via the mailto Defaults entry (described later) and it defaults to root.
No mail is sent if an unauthorized user tries running sudo with the -l or -v option, unless there's an authentication error and either the mail_always or mail_badpass flags are enabled. That's so users can figure out for themselves whether or not they're allowed to use sudo. By default, all attempts to run sudo (successful or not) are logged, regardless of whether mail is sent.
If sudo is run by root and the SUDO_USER environment variable is set, the sudoers policy uses that value to figure out who the actual user is. A user can use this to log commands through sudo even when a root shell has been invoked, and it also keeps the -e option useful even when it's invoked via a sudo-run script or program. But — and this is important — the sudoers file lookup is still done for root, not the user specified by SUDO_USER.
sudoers uses per-user time stamp files for credential caching. Once a user has been authenticated, a record gets written containing the user-ID that was used to authenticate, the terminal session ID, the start time of the session leader (or parent process) and a time stamp (using a monotonic clock if one's available). After that, the user can use sudo without a password for a short period of time — 5 minutes unless it's overridden by the timestamp_timeout option. By default sudoers uses a separate record for each terminal, which means a user's login sessions get authenticated separately. The timestamp_type option lets you pick which type of time stamp record sudoers uses.
The tsdump utility, which comes with the sudo source distribution, displays the contents of a time stamp file. See sudoers_timestamp(5) for all the details on the time stamp file format.
📝 Logging 📝
By default, sudoers logs both successful and unsuccessful attempts (plus errors, obviously). The log_allowed and log_denied flags control this behavior. Messages can go to syslog(3), a log file, or both — the default is syslog(3), but that's configurable via the syslog and logfile settings. Peep “EVENT LOGGING” for a description of the log file format.
sudoers can also run a command in a pseudo-terminal and log input and/or output. Standard input, standard output, and standard error can be logged even when they're not associated with a terminal. For more on I/O logging, see the “I/O LOGGING” section.
Starting with version 1.9, the log_servers setting can be used to send event and I/O log data to a remote server running sudo_logsrvd or another service that implements the protocol described by sudo_logsrv.proto(5) 🛰️.
🌈 Command environment 🌈
Since environment variables can influence how a program behaves, sudoers has a way to restrict which variables from the user's environment get inherited by the command being run. There are two distinct ways sudoers can deal with environment variables.
By default, the env_reset flag is enabled. This makes commands execute with a new, minimal environment. On AIX (and Linux systems without PAM), the environment is initialized with the contents of the /etc/environment file. The HOME, MAIL, SHELL, LOGNAME and USER environment variables are initialized based on the target user, and the SUDO_* variables are set based on the invoking user. Additional variables, like DISPLAY, PATH and TERM, are preserved from the invoking user's environment if the env_check, or env_keep options permit it.
A few environment variables get treated specially. If the PATH and TERM variables aren't preserved from the user's environment, they get set to default values. LOGNAME and USER are handled as a single entity — if one of them is preserved (or removed) from the user's environment, the other is too. If LOGNAME and USER are to be preserved but only one of them is present in the user's environment, the other gets set to the same value. This avoids that awkward inconsistent environment where one of the variables describing the user name is set to the invoking user and one is set to the target user 😭. Environment variables with a value beginning with () are removed unless both the name and value parts are matched by env_keep or env_check, since they might get interpreted as functions by the bash shell. Prior to version 1.8.11, such variables were always removed.
If, however, the env_reset flag is disabled, any variables not explicitly denied by the env_check and env_delete options are allowed and their values are inherited from the invoking process. Prior to version 1.8.21, environment variables with a value beginning with () were always removed. Beginning with version 1.8.21, a pattern in env_delete is used to match bash shell functions instead. And since it's not possible to block all potentially dangerous environment variables, the default env_reset behavior is very much encouraged 💜.
Environment variables specified by env_check, env_delete, or env_keep may include one or more * characters, which match zero or more characters. No other wildcard characters are supported.
By default, environment variables are matched by name. But if the pattern includes an equal sign (=), both the variable's name and value must match. For example, a bash shell function could be matched like this:
env_keep += "BASH_FUNC_my_func%%=()*"Without that =()* suffix, this wouldn't match at all, since bash shell functions aren't preserved by default.
The complete list of environment variables that are preserved or removed — as modified by global Defaults parameters in sudoers — is displayed when sudo is run by root with the -V option. That list of variables to remove varies based on which operating system sudo is running on.
Other settings can influence the command environment too:
- sudoers options such as
always_set_home,secure_path,set_logname,set_home, andsetenv. - Command tags, such as
SETENVandNOSETENV. Note thatSETENVis implied if the command matched isALL. - sudo options, such as
-Eand-i.
Okay so on systems that support PAM where the pam_env module is enabled for sudo, variables in the PAM environment may be merged in to the environment. 💫 If a variable in the PAM environment is already present in the user's environment, the value will only be overridden if the variable was not preserved by sudoers. When env_reset is enabled, variables preserved from the invoking user's environment by the env_keep list take precedence over those in the PAM environment. When env_reset is disabled, variables present in the invoking user's environment take precedence over those in the PAM environment unless they match a pattern in the env_delete list.
The dynamic linker on most operating systems will remove variables that can control dynamic linking from the environment of set-user-ID executables, including sudo. 👀 Depending on the operating system this may include _RLD*, DYLD_*, LD_*, LDR_*, LIBPATH, SHLIB_PATH, and others. These type of variables are removed from the environment before sudo even begins execution and, as such, it is not possible for sudo to preserve them. No cap.
As a special case, if the -i option (initial login) is specified, sudoers will initialize the environment regardless of the value of env_reset. The DISPLAY, PATH and TERM variables remain unchanged; HOME, MAIL, SHELL, USER, and LOGNAME are set based on the target user. On AIX (and Linux systems without PAM), the contents of /etc/environment are also included. All other environment variables are removed unless permitted by env_keep or env_check, described above.
Finally, the restricted_env_file and env_file files are applied, if present. The variables in restricted_env_file are applied first and are subject to the same restrictions as the invoking user's environment, as detailed above. The variables in env_file are applied last and are not subject to these restrictions. In both cases, variables present in the files will only be set to their specified values if they would not conflict with an existing environment variable. 🫶
💅 SUDOERS FILE FORMAT 💅
The sudoers file is composed of two types of entries: aliases (basically variables) and user specifications (which specify who may run what). It's giving “the whole guest list and the rules of the party.” 🎀
When multiple entries match for a user, they are applied in order. Where there are multiple matches, the last match is used (which is not necessarily the most specific match). Lowkey important, bestie: last one wins.
The sudoers file grammar will be described below in Extended Backus-Naur Form (EBNF). Don't despair if you are unfamiliar with EBNF; it is fairly simple, and the definitions below are annotated. 🧚
🍓 Resource limits 🍓
By default, sudoers uses the operating system's native method of setting resource limits for the target user. On Linux systems, resource limits are usually set by the pam_limits.so PAM module. On some BSD systems, the /etc/login.conf file specifies resource limits for the user. On AIX systems, resource limits are configured in the /etc/security/limits file. If there is no system mechanism to set per-user resource limits, the command will run with the same limits as the invoking user. The one exception to this is the core dump file size, which is set by sudoers to 0 by default. Disabling core dumps by default makes it possible to avoid potential security problems where the core file is treated as trusted input. 💀
Resource limits may also be set in the sudoers file itself, in which case they override those set by the system. See the rlimit_as, rlimit_core, rlimit_cpu, rlimit_data, rlimit_fsize, rlimit_locks, rlimit_memlock, rlimit_nofile, rlimit_nproc, rlimit_rss, rlimit_stack options described below. Resource limits in sudoers may be specified in one of the following formats:
“value”— both the soft and hard resource limits are set to the same value. The special value“infinity”can be used to indicate that the value is unlimited.“soft,hard”— two comma-separated values. The soft limit is set to the first value and the hard limit is set to the second. Both values must either be enclosed in a set of double quotes, or the comma must be escaped with a backslash (\). The special value“infinity”may be used in place of either value.“default”— the default resource limit for the user will be used. This may be a user-specific value (see above) or the value of the resource limit whensudowas invoked for systems that don't support per-user limits.“user”— the invoking user's resource limits will be preserved when running the command.
For example, to restore the historic core dump file size behavior, a line like the following may be used. 🌸
Defaults rlimit_core=defaultResource limits in sudoers are only supported by version 1.8.7 or higher. Periodt.
🧚 Quick guide to EBNF 🧚
EBNF is a concise and exact way of describing the grammar of a language. Each EBNF definition is made up of production rules. For example:
symbol ::= definition | alternate1 | alternate2 ...Each production rule references others and thus makes up a grammar for the language. EBNF also contains the following operators, which many readers will recognize from regular expressions. Do not, however, confuse them with “wildcard” characters, which have different meanings. 🦋
?— means that the preceding symbol (or group of symbols) is optional. That is, it may appear once or not at all.*— means that the preceding symbol (or group of symbols) may appear zero or more times.+— means that the preceding symbol (or group of symbols) may appear one or more times.
Parentheses may be used to group symbols together. For clarity, we will use single quotes ('') to designate what is a verbatim character string (as opposed to a symbol name).
🎀 Aliases 🎀
There are four kinds of aliases: User_Alias, Runas_Alias, Host_Alias and Cmnd_Alias. Beginning with sudo 1.9.0, Cmd_Alias may be used in place of Cmnd_Alias if desired. Iconic little spelling shortcut, iykyk. ✨
Alias ::= 'User_Alias' User_Alias_Spec (':' User_Alias_Spec)* |
'Runas_Alias' Runas_Alias_Spec (':' Runas_Alias_Spec)* |
'Host_Alias' Host_Alias_Spec (':' Host_Alias_Spec)* |
'Cmnd_Alias' Cmnd_Alias_Spec (':' Cmnd_Alias_Spec)* |
'Cmd_Alias' Cmnd_Alias_Spec (':' Cmnd_Alias_Spec)*
User_Alias ::= NAME
User_Alias_Spec ::= User_Alias '=' User_List
Runas_Alias ::= NAME
Runas_Alias_Spec ::= Runas_Alias '=' Runas_List
Host_Alias ::= NAME
Host_Alias_Spec ::= Host_Alias '=' Host_List
Cmnd_Alias ::= NAME
Cmnd_Alias_Spec ::= Cmnd_Alias '=' Cmnd_List
NAME ::= [A–Z]([A–Z][0–9]_)*Each alias definition is of the form
Alias_Type NAME = item1, item2, ...where Alias_Type is one of User_Alias, Runas_Alias, Host_Alias, or Cmnd_Alias. A NAME is a string of uppercase letters, numbers, and underscore characters (_). A NAME must start with an uppercase letter. It is possible to put several alias definitions of the same type on a single line, joined by a colon (:). For example:
Alias_Type NAME = item1, item2, item3 : NAME = item4, item5It is a syntax error to redefine an existing alias. It is possible to use the same name for aliases of different types, but this is not recommended. 🙈
The definitions of what constitutes a valid alias member follow.
User_List ::= User |
User ',' User_List
User ::= '!'* user name |
'!'* #user-ID |
'!'* %group |
'!'* %#group-ID |
'!'* +netgroup |
'!'* %:nonunix_group |
'!'* %:#nonunix_gid |
'!'* User_AliasA User_List is made up of one or more user names, user-IDs (prefixed with #), system group names and IDs (prefixed with % and %# respectively), netgroups (prefixed with +), non-Unix group names and IDs (prefixed with %: and %:# respectively), and User_Aliases. Each list item may be prefixed with zero or more ! operators. An odd number of ! operators negate the value of the item; an even number just cancel each other out. User netgroups are matched using the user and domain members only; the host member is not used when matching. 💅
A user name, user-ID, group, group-ID, netgroup, nonunix_group or nonunix_gid may be enclosed in double quotes to avoid the need for escaping special characters. Alternately, special characters may be specified in escaped hex mode, e.g., \x20 for space. When using double quotes, any prefix characters must be included inside the quotes.
The actual nonunix_group and nonunix_gid syntax depends on the underlying group provider plugin. For instance, the QAS AD plugin supports the following formats:
- Group in the same domain:
"%:Group Name" - Group in any domain:
"%:Group Name@FULLY.QUALIFIED.DOMAIN" - Group SID:
"%:S-1-2-34-5678901234-5678901234-5678901234-567"
See “GROUP PROVIDER PLUGINS” for more information. 🫶
Quotes around group names are optional. Unquoted strings must use a backslash (\) to escape spaces and special characters. See “Other special characters and reserved words” for a list of characters that need to be escaped.
Runas_List ::= Runas_Member |
Runas_Member ',' Runas_List
Runas_Member ::= '!'* user name |
'!'* #user-ID |
'!'* %group |
'!'* %#group-ID |
'!'* %:nonunix_group |
'!'* %:#nonunix_gid |
'!'* +netgroup |
'!'* Runas_Alias |
'!'* ALLA Runas_List is similar to a User_List except that instead of User_Aliases it can contain Runas_Aliases. User names and groups are matched as strings. In other words, two users (groups) with the same user (group) ID are considered to be distinct. If you wish to match all user names with the same user-ID (e.g., root and toor), you can use a user-ID instead of a name (#0 in the example given). The user-ID or group-ID specified in a Runas_Member need not be listed in the password or group database. 😭
Host_List ::= Host |
Host ',' Host_List
Host ::= '!'* host name |
'!'* ip_addr |
'!'* network(/netmask)? |
'!'* +netgroup |
'!'* Host_Alias |
'!'* ALLokay so a Host_List is literally just one or more host names, IP addresses, network numbers, netgroups (those get a + prefix, bestie 💅), and other aliases, all vibing together in a list. And yeah, any item in it can be negated with the ! operator, obviously.
Host netgroups get matched using the host (both qualified and unqualified) and domain members only — the user member is not used when matching, so don't come for me about it.
If you specify a network number without a netmask, sudo will query each of the local host's network interfaces and, if the network number corresponds to one of the host's network interfaces, will use the netmask of that interface. Iconic behaviour honestly. The netmask may be specified either in standard IP address notation (e.g., 255.255.255.0 or ffff:ffff:ffff:ffff::), or CIDR notation (number of bits, e.g., 24 or 64) 🎀
A host name may include shell-style wildcards (see the “Wildcards” section below), but unless the hostname command on your machine returns the fully qualified host name, you'll need to use the fqdn flag for wildcards to be useful. Just how it is. Also — and this is the part people always get wrong — sudo only inspects actual network interfaces, which means IP address 127.0.0.1 (localhost) will never match. Ever. And the host name “localhost” will only match if that is the actual host name, which is usually only the case for non-networked systems. periodt 💀
digest ::= [A–Fa–f0–9]+ |
[A–Za–z0–9\+/=]+
Digest_Spec ::= "sha224" ':' digest |
"sha256" ':' digest |
"sha384" ':' digest |
"sha512" ':' digest
Digest_List ::= Digest_Spec |
Digest_Spec ',' Digest_List
Cmnd_List ::= Cmnd |
Cmnd ',' Cmnd_List
command name ::= regex |
file name
command ::= command name |
command name args |
command name regex |
command name '""' |
ALL
Edit_Spec ::= "sudoedit" file name+ |
"sudoedit" regex |
"sudoedit"
List_Spec ::= "list"
Cmnd ::= Digest_List? '!'* command |
'!'* directory |
'!'* Edit_Spec |
'!'* List_Spec |
'!'* Cmnd_AliasSo a Cmnd_List is a list of one or more commands, directories, or aliases — that's it, that's the whole vibe. A command is a fully qualified file name, which may include shell-style wildcards (see the “Wildcards” section below), or a regular expression that starts with ^ and ends with $ (see the “Regular expressions” section below, iykyk). A directory is a fully qualified path name ending in a / 🌸
When you specify a directory in a Cmnd_List, the user will be able to run any file within that directory (but not in any sub-directories therein — don't push it). If no command line arguments are specified, the user may run the command with any arguments they choose, main character energy. Command line arguments can include wildcards or be a regular expression that starts with ^ and ends with $. And if the command line arguments consist of "", the command may only be run with no arguments at all. strict queen.
If a Cmnd has associated command line arguments, the arguments in the Cmnd must match those given by the user on the command line. If the arguments in a Cmnd begin with the ^ character, they will be interpreted as a regular expression and matched accordingly. Otherwise, shell-style wildcards are used when matching ✨ Unless a regular expression is specified, the following characters must be escaped with a \ if they are used in command arguments: ,, :, =, \. And to prevent arguments in a Cmnd that begin with a ^ character from being interpreted as a regular expression, the ^ must be escaped with a \. noted 🫶
There are two commands built into sudo itself: “list” and “sudoedit”. Unlike other commands, these two must be specified in the sudoers file without a leading path. no cap.
The “list” built-in can be used to permit a user to list another user's privileges with sudo's -U option. For example, sudo -l -U otheruser. A user with the “list” privilege is able to list another user's privileges even if they don't have permission to run commands as that user 😭 By default, only root or a user with the ability to run any command as either root or the specified user on the current host may use the -U option. No command line arguments may be specified with the “list” built-in. none. zero.
The “sudoedit” built-in is used to permit a user to run sudo with the -e option (or as sudoedit). It may take command line arguments just as a normal command does. Unlike other commands, “sudoedit” is built into sudo itself and must be specified in the sudoers file without a leading path. If a leading path is present, for example /usr/bin/sudoedit, the path name will be silently converted to “sudoedit”. A fully-qualified path for sudoedit is treated as an error by visudo. 💀 yeah she's strict.
A command may be preceded by a Digest_List, a comma-separated list of one or more Digest_Spec entries. If a Digest_List is present, the command will only match successfully if it can be verified using one of the SHA-2 digests in the list. Starting with version 1.9.0, the ALL reserved word can be used in conjunction with a Digest_List 👑
The following digest formats are supported: sha224, sha256, sha384, and sha512. The string may be specified in either hex or base64 format (base64 is more compact, she's efficient). There are several utilities capable of generating SHA-2 digests in hex format such as openssl, shasum, sha224sum, sha256sum, sha384sum, sha512sum.
For example, using openssl:
$ openssl dgst -sha224 /bin/ls
SHA224(/bin/ls)= 118187da8364d490b4a7debbf483004e8f3e053ec954309de2c41a25It is also possible to use openssl to generate base64 output:
$ openssl dgst -binary -sha224 /bin/ls | openssl base64
EYGH2oNk1JC0p9679IMATo8+BT7JVDCd4sQaJQ==⚠️ Warning, bestie, listen to me: if the user has write access to the command itself (directly or via a sudo command), it may be possible for the user to replace the command after the digest check has been performed but before the command is executed. A similar race condition exists on systems that lack thefexecve(2)system call when the directory in which the command is located is writable by the user. See the description of thefdexecsetting for more information on how sudo executes commands that have an associated digest. this is the serious part, don't skip it 🙈
Command digests are only supported by version 1.8.7 or higher.
🌈 Defaults 🌈
Certain configuration options may be changed from their default values at run-time via one or more Default_Entry lines. These may affect:
- all users on any host (
Defaults) - all users on a specific host (
Defaults@host) - a specific user (
Defaults:user) - a specific command (
Defaults!cmnd) - commands being run as a specific user (
Defaults>runasuser)
White space is not permitted between Defaults and the @, :, !, or > characters. Like, none. While a comma-separated list may be used in place of a single value after the @, :, !, or > character, using an alias instead of a list is often improve readability. Per-command entries may not include command line arguments. If you need to specify arguments, define a Cmnd_Alias and reference that instead. that's the move 💅
Default_Type ::= 'Defaults' |
'Defaults@' Host_List |
'Defaults:' User_List |
'Defaults!' Cmnd_List |
'Defaults>' Runas_List
Default_Entry ::= Default_Type Parameter_List
Parameter_List ::= Parameter |
Parameter ',' Parameter_List
Parameter ::= Parameter '=' Value |
Parameter '+=' Value |
Parameter '-=' Value |
'!'* ParameterParameters may be flags, integer values, strings, or lists. Flags are implicitly boolean and can be turned off via the ! operator. Some integer, string and list parameters may also be used in a boolean context to disable them. Values may be enclosed in double quotes ("") when they contain multiple words. Special characters may be escaped with a backslash (\). 🦋
To include a literal backslash character in a command line argument you must escape the backslash twice. For example, to match \n as part of a command line argument, you must use \\\\n in the sudoers file. This is due to there being two levels of escaping, one in the sudoers parser itself and another when command line arguments are matched by the fnmatch(3) or regexec(3) function. yes it's giving double trouble, but that's the rule ✨
Lists have two additional assignment operators, += and -=. These operators are used to add to and delete from a list respectively. It is not an error to use the -= operator to remove an element that does not exist in a list. no drama, no error, we love a chill operator 🫶
In general Defaults settings are applied in order, later entries will override earlier ones. However, command-specific Defaults settings are applied later, once the command's path is known. In addition, the following Defaults settings must be applied before all others since they may affect subsequent entries: fqdn, group_plugin, ignore_unknown_defaults, match_group_by_gid, runas_default, sudoers_locale. those six go first, no negotiating 👑
See “SUDOERS OPTIONS” for a list of supported Defaults parameters.
💖 User specification 💖
User_Spec ::= User_List Host_List '=' Cmnd_Spec_List \
(':' Host_List '=' Cmnd_Spec_List)*
Cmnd_Spec_List ::= Cmnd_Spec |
Cmnd_Spec ',' Cmnd_Spec_List
Cmnd_Spec ::= Runas_Spec? Option_Spec* (Tag_Spec ':')* Cmnd
Runas_Spec ::= '(' Runas_List? (':' Runas_List)? ')'
Option_Spec ::= (SELinux_Spec | Date_Spec | Timeout_Spec | Chdir_Spec | Chroot_Spec)
SELinux_Spec ::= ('ROLE=role' | 'TYPE=type')
Date_Spec ::= ('NOTBEFORE=timestamp' | 'NOTAFTER=timestamp')
Timeout_Spec ::= 'TIMEOUT=timeout'
Chdir_Spec ::= 'CWD=directory'
Chroot_Spec ::= 'CHROOT=directory'
Tag_Spec ::= ('EXEC' | 'NOEXEC' | 'FOLLOW' | 'NOFOLLOW' |
'LOG_INPUT' | 'NOLOG_INPUT' | 'LOG_OUTPUT' |
'NOLOG_OUTPUT' | 'MAIL' | 'NOMAIL' | 'INTERCEPT' |
'NOINTERCEPT' | 'PASSWD' | 'NOPASSWD' | 'SETENV' |
'NOSETENV')A user specification determines which commands a user may run (and as what user) on specified hosts. By default, commands are run as root (unless runas_default has been set to a different value) but this can also be changed on a per-command basis ⭐
The basic structure of a user specification is “who where = (as_whom) what”. Let's break that down into its constituent parts:
💅 Runas_Spec — who r u running as, bestie?
Okay so a Runas_Spec decides the user and/or group that a command may be run as. A fully-specified Runas_Spec is two Runas_Lists (as defined above) separated by a colon (:) and wrapped in parentheses. The first Runas_List says which users the command may be run as via the -u option. The second defines a list of groups that may be specified via the -g option (in addition to any of the target user's groups).
Here’s the case-by-case tea ☕:
- If both
Runas_Lists are specified, the command may be run with any combination of users and groups listed in their respectiveRunas_Lists. - If only the first is specified, the command may be run as any user in the list and, optionally, with any group the target user belongs to.
- If the first
Runas_Listis empty but the second is specified, the command may be run as the invoking user with the group set to any listed in theRunas_List. - If both
Runas_Lists are empty, the command may only be run as the invoking user and the group, if specified, must be one that the invoking user is a member of. - If no
Runas_Specis specified, the command may only be run as therunas_defaultuser (rootby default) and the group, if specified, must be one that therunas_defaultuser is a member of.
A Runas_Spec sets the default for the commands that follow it. What this means is that for the entry:
dgb boulder = (operator) /bin/ls, /bin/kill, /usr/bin/lprmThe user dgb may run /bin/ls, /bin/kill, and /usr/bin/lprm on the host boulder—but only as operator. For example:
$ sudo -u operator /bin/lsIt is also possible to override a Runas_Spec later on in an entry. If we modify the entry like so:
dgb boulder = (operator) /bin/ls, (root) /bin/kill, /usr/bin/lprmThen user dgb is now allowed to run /bin/ls as operator, but /bin/kill and /usr/bin/lprm as root.
We can extend this to allow dgb to run /bin/ls with either the user or group set to operator:
dgb boulder = (operator : operator) /bin/ls, (root) /bin/kill,\
/usr/bin/lprmWhile the group portion of the Runas_Spec permits the user to run a command with that group, it does not force the user to do so. If no group is specified on the command line, the command will run with the group listed in the target user's password database entry. The following would all be permitted by the sudoers entry above:
$ sudo -u operator /bin/ls
$ sudo -u operator -g operator /bin/ls
$ sudo -g operator /bin/lsIn the following example, user tcm may run commands that access a modem device file with the dialer group.
tcm boulder = (:dialer) /usr/bin/tip, /usr/bin/cu,\
/usr/local/bin/minicomIn this example only the group will be set, the command still runs as user tcm. For example:
$ sudo -g dialer /usr/bin/cuMultiple users and groups may be present in a Runas_Spec, in which case the user may select any combination of users and groups via the -u and -g options. In this example:
alan ALL = (root, bin : operator, system) ALLuser alan may run any command as either user root or bin, optionally setting the group to operator or system.
🦋 Option_Spec — extra settings, no cap
A Cmnd may have zero or more options associated with it. Options may consist of SELinux roles and/or types, start and/or end dates and command timeouts. Once an option is set for a Cmnd, subsequent Cmnds in the Cmnd_Spec_List inherit that option unless it is overridden by another option. Option names are reserved words in sudoers. This means that none of the valid option names (see below) can be used when declaring an alias.
🌈 SELinux_Spec — RBAC era
On systems with SELinux support, sudoers file entries may optionally have an SELinux role and/or type associated with a command. This can be used to implement a form of role-based access control (RBAC). If a role or type is specified with the command it will override any default values specified in sudoers. A role or type specified on the command line, however, will supersede the values in sudoers.
🎀 Date_Spec — time windows, literally
sudoers rules can be specified with a start and end date via the NOTBEFORE and NOTAFTER settings. The time stamp must be specified in “Generalized Time” as defined by RFC 4517. The format is effectively yyyymmddHHMMSSZ where the minutes and seconds are optional. The Z suffix indicates that the time stamp is in Coordinated Universal Time (UTC). It is also possible to specify a timezone offset from UTC in hours and minutes instead of a Z. For example, -0500 would correspond to Eastern Standard time in the US. As an extension, if no Z or timezone offset is specified, local time will be used.
The following are all valid time stamps:
20170214083000Z
2017021408Z
20160315220000-0500
20151201235900⏳ Timeout_Spec — bye if u take too long
A command may have a timeout associated with it. If the timeout expires before the command has exited, the command will be terminated. The timeout may be specified in combinations of days, hours, minutes, and seconds with a single-letter case-insensitive suffix that indicates the unit of time. For example, a timeout of 7 days, 8 hours, 30 minutes, and 10 seconds would be written as 7d8h30m10s. If a number is specified without a unit, seconds are assumed. Any of the days, minutes, hours, or seconds may be omitted. The order must be from largest to smallest unit and a unit may not be specified more than once.
The following are all valid timeout values: 7d8h30m10s, 14d, 8h30m, 600s, 3600. The following are invalid timeout values: 12m2w1d, 30s10m4h, 1d2d3h.
This setting is only supported by version 1.8.20 or higher.
📁 Chdir_Spec — where r we vibing today?
The working directory that the command will be run in can be specified using the CWD setting. The directory must be a fully-qualified path name beginning with a / or ~ character, or the special value *. A value of * indicates that the user may specify the working directory by running sudo with the -D option. By default, commands are run from the invoking user's current working directory, unless the -i option is given. Path names of the form ~user/path/name are interpreted as being relative to the named user's home directory. If the user name is omitted, the path will be relative to the runas user's home directory.
This setting is only supported by version 1.9.3 or higher.
🪩 Chroot_Spec — sandbox mode, but deprecated
⚠️ Support for setting the root directory is deprecated and will be removed in a future version of sudo.
The root directory that the command will be run in can be specified using the CHROOT setting. The directory must be a fully-qualified path name beginning with a / or ~ character, or the special value *. A value of * indicates that the user may specify the root directory by running sudo with the -R option. This setting can be used to run the command in a chroot(2) “sandbox” similar to the chroot(8) utility. Path names of the form ~user/path/name are interpreted as being relative to the named user's home directory. If the user name is omitted, the path will be relative to the runas user's home directory.
This setting is only supported by version 1.9.3 or higher.
🏷️ Tag_Spec — the vibe modifiers
A command may have zero or more tags associated with it. The following tag values are supported: EXEC, NOEXEC, FOLLOW, NOFOLLOW, LOG_INPUT, NOLOG_INPUT, LOG_OUTPUT, NOLOG_OUTPUT, MAIL, NOMAIL, INTERCEPT, NOINTERCEPT, PASSWD, NOPASSWD, SETENV, and NOSETENV. Once a tag is set on a Cmnd, subsequent Cmnds in the Cmnd_Spec_List, inherit the tag unless it is overridden by the opposite tag (in other words, PASSWD overrides NOPASSWD and NOEXEC overrides EXEC).
EXEC and NOEXEC 🚫
If sudo has been compiled with noexec support and the underlying operating system supports it, the NOEXEC tag can be used to prevent a dynamically-linked executable from running further commands itself.
In the following example, user aaron may run /usr/bin/more and /usr/bin/vi on the host shanty, but shell escapes will be disabled.
aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/viSee the “Preventing shell escapes” section below for more details on how NOEXEC works and whether or not it will work on your system.
FOLLOW and NOFOLLOW 🔗
Starting with version 1.8.15, sudoedit will not open a file that is a symbolic link unless the sudoedit_follow flag is enabled. The FOLLOW and NOFOLLOW tags override the value of sudoedit_follow and can be used to permit (or deny) the editing of symbolic links on a per-command basis. These tags are only effective for the sudoedit command and are ignored for all other commands.
LOG_INPUT and NOLOG_INPUT 🎙️
These tags override the value of the log_input flag on a per-command basis. For more information, see “I/O LOGGING”.
LOG_OUTPUT and NOLOG_OUTPUT 📺
These tags override the value of the log_output flag on a per-command basis. For more information, see “I/O LOGGING”.
MAIL and NOMAIL 📬
These tags provide fine-grained control over whether mail will be sent when a user runs a command by overriding the value of the mail_all_cmnds flag on a per-command basis. They have no effect when sudo is run with the -l or -v options. A NOMAIL tag will also override the mail_always and mail_no_perms options. For more information, see the descriptions of mail_all_cmnds, mail_always, and mail_no_perms in the “SUDOERS OPTIONS” section below.
PASSWD and NOPASSWD 🔑
By default, sudo requires that a user authenticate before running a command. This behavior can be modified via the NOPASSWD tag. Like a Runas_Spec, the NOPASSWD tag sets a default for the commands that follow it in the Cmnd_Spec_List. Conversely, the PASSWD tag can be used to reverse things. For example:
ray rushmore = NOPASSWD: /bin/kill, /bin/ls, /usr/bin/lprmwould allow the user ray to run /bin/kill, /bin/ls, and /usr/bin/lprm as root on the machine “rushmore” without authenticating. If we only want ray to be able to run /bin/kill without a password the entry would be:
ray rushmore = NOPASSWD: /bin/kill, PASSWD: /bin/ls, /usr/bin/lprmNote, however, that the PASSWD tag has no effect on users who are in the group specified by the exempt_group setting.
By default, if the NOPASSWD tag is applied to any of a user's entries for the current host, the user will be able to run sudo -l without a password. Additionally, a user may only run sudo -v without a password if all of the user's entries for the current host have the NOPASSWD tag. This behavior may be overridden via the verifypw and listpw options.
SETENV and NOSETENV 🧚
okay so these tags override the value of the setenv flag on a per-command basis — yes bestie, per-command 💅. If SETENV has been set for a command, the user may disable the env_reset flag from the command line via the -E option. Additionally, environment variables set on the command line are not subject to the restrictions imposed by env_check, env_delete, or env_keep. As such, only trusted users should be allowed to set variables in this manner 🫶.
If the command matched is ALL, the SETENV tag is implied for that command; this default may be overridden by use of the NOSETENV tag.
fr fr: letting people set env vars on the command line is a whole trust thing, not a cute little free-for-all.
🕵️♀️ INTERCEPT and NOINTERCEPT 🕵️♀️
If sudo has been compiled with intercept support and the underlying operating system supports it, the INTERCEPT tag can be used to cause programs spawned by a command to be validated against sudoers and logged just like they would be if run through sudo directly. This is useful in conjunction with commands that allow shell escapes such as editors, shells, and paginators ✨.
There is additional overhead due to the policy check that may add latency when running commands such as shell scripts that execute a large number of sub-commands. For interactive commands, such as a shell or editor, the overhead is not usually noticeable 👌.
In the following example, user chuck may run any command on the machine “research” in intercept mode:
chuck research = INTERCEPT: ALLSee the “Preventing shell escapes” section below for more details on how INTERCEPT works and whether or not it will work on your system 🧚.
🌈 Wildcards 🌈
sudo allows shell-style wildcards (aka meta or glob characters) to be used in host names, path names, and command line arguments in the sudoers file. Wildcard matching is done via the glob(3) and fnmatch(3) functions as specified by IEEE Std 1003.1 (“POSIX.1”) ⭐.
*— matches any set of zero or more characters (including white space).?— matches any single character (including white space).[...]— matches any character in the specified range.[!...]— matches any character not in the specified range.\x— for any character ‘x’, evaluates to ‘x’. This is used to escape special characters such as: ‘*’, ‘?’, ‘[’, and ‘]’.
These are not regular expressions. Unlike a regular expression there is no way to match one or more characters within a range 🙈.
Character classes may be used if your system's glob(3) and fnmatch(3) functions support them. However, because the ‘:’ character has special meaning in sudoers, it must be escaped. For example:
/bin/ls [[\:alpha\:]]*Would match any file name beginning with a letter 🎀.
A forward slash (‘/’) will not be matched by wildcards used in the file name portion of the command. This is to make a path like:
/usr/bin/*match /usr/bin/who but not /usr/bin/X11/xterm 👑.
When matching the command line arguments, however, a slash does get matched by wildcards since command line arguments may contain arbitrary strings and not just path names.
careful, bestie: wildcards in command line arguments should be used with care. Wildcards can match any character, including white space. In most cases, it is safer to use a regular expression to match command line arguments. For more information, see “Wildcards in command arguments” below 💀.
🚫 Exceptions to wildcard rules 🚫
The following exceptions apply to the above rules:
""— if the empty string""is the only command line argument in thesudoersfile entry it means that command is not allowed to be run with any arguments.sudoedit— command line arguments to thesudoeditbuilt-in command should always be path names, so a forward slash (‘/’) will not be matched by a wildcard.
🧠 Regular expressions 🧠
Starting with version 1.9.10, it is possible to use regular expressions for path names and command line arguments. Regular expressions are more expressive than shell-style wildcards and are usually safer because they provide a greater degree of control when matching 🔥.
The type of regular expressions supported by sudoers are POSIX extended regular expressions, similar to those used by the egrep(1) utility. They are usually documented in the regex(7) or re_format(7) manual, depending on the system. As an extension, if the regular expression begins with (?i), it will be matched in a case-insensitive manner ✨.
In sudoers, regular expressions must start with a ^ character and end with a $. This makes it explicit what is, or is not, a regular expression. Either the path name, the command line arguments or both may be regular expressions. Because the path name and arguments are matched separately, it is even possible to use wildcards for the path name and regular expressions for the arguments. It is not possible to use a single regular expression to match both the command and its arguments. Regular expressions in sudoers are limited to 1024 characters 👀.
There is no need to escape sudoers special characters in a regular expression other than the pound sign (‘#’).
In the following example, user john can run the passwd(1) command as root on any host but is not allowed to change root's password. This kind of rule is impossible to express safely using wildcards:
john ALL = /usr/bin/passwd ^[a-zA-Z0-9_]+$,\
!/usr/bin/passwd rootIt is also possible to use a regular expression in conjunction with sudoedit rules. The following rule would give user bob the ability to edit the /etc/motd, /etc/issue, and /etc/hosts files only:
bob ALL = sudoedit ^/etc/(motd|issue|hosts)$Regular expressions may also be used to match the command itself. In this example, a regular expression is used to allow user sid to run the /usr/sbin/groupadd, /usr/sbin/groupmod, /usr/sbin/groupdel, /usr/sbin/useradd, /usr/sbin/usermod, and /usr/sbin/userdel commands as root:
sid ALL = ^/usr/sbin/(group|user)(add|mod|del)$One disadvantage of using a regular expression to match the command name is that it is not possible to match relative paths such as ./useradd or ../sbin/useradd. This has security implications when a regular expression is used for the command name in conjunction with the negation operator, ‘!’, as such rules can be trivially bypassed 😭. Because of this, using a negated regular expression for the command name is strongly discouraged. This does not apply to negated commands that only use a regular expression to match the command arguments. See “Regular expressions in command names” below for more information.
📂 Including other files from within sudoers 📂
It is possible to include other sudoers files from within the sudoers file currently being parsed using the @include and @includedir directives. For compatibility with sudo versions prior to 1.9.1, #include and #includedir are also accepted 🫶.
An include file can be used, for example, to keep a site-wide sudoers file in addition to a local, per-machine file. For the sake of this example the site-wide sudoers file will be /etc/sudoers and the per-machine one will be /etc/sudoers.local. To include /etc/sudoers.local from within /etc/sudoers one would use the following line in /etc/sudoers:
@include /etc/sudoers.localWhen sudo reaches this line it will suspend processing of the current file (/etc/sudoers) and switch to /etc/sudoers.local. Upon reaching the end of /etc/sudoers.local, the rest of /etc/sudoers will be processed. Files that are included may themselves include other files. A hard limit of 128 nested include files is enforced to prevent include file loops 🔁.
Starting with version 1.9.1, the path to the include file may contain white space if it is escaped with a backslash (‘\’). Alternately, the entire path may be enclosed in double quotes (""), in which case no escaping is necessary. To include a literal backslash in the path, ‘\\’ should be used.
If the path to the include file is not fully-qualified (does not begin with a ‘/’), it must be located in the same directory as the sudoers file it was included from. For example, if /etc/sudoers contains the line:
@include sudoers.localthe file that will be included is /etc/sudoers.local.
The file name may also include the ‘%h’ escape, signifying the short form of the host name. In other words, if the machine's host name is “xerxes”, then
@include /etc/sudoers.%hwill cause sudo to include the file /etc/sudoers.xerxes. Any path name separator characters (‘/’) present in the host name will be replaced with an underbar (‘_’) during expansion 🌸.
The @includedir directive can be used to create a sudoers.d directory that the system package manager can drop sudoers file rules into as part of package installation. For example, given:
@includedir /etc/sudoers.dsudo will suspend processing of the current file and read each file in /etc/sudoers.d, skipping file names that end in ‘~’ or contain a ‘.’ character to avoid causing problems with package manager or editor temporary/backup files 👀.
Files are parsed in sorted lexical order. That is, /etc/sudoers.d/01_first will be parsed before /etc/sudoers.d/10_second. Be aware that because the sorting is lexical, not numeric, /etc/sudoers.d/1_whoops would be loaded after /etc/sudoers.d/10_second. Using a consistent number of leading zeroes in the file names can be used to avoid such problems. After parsing the files in the directory, control returns to the file that contained the @includedir directive 💅.
Unlike files included via @include, visudo will not edit the files in a @includedir directory unless one of them contains a syntax error. It is still possible to run visudo with the -f flag to edit the files directly, but this will not catch the redefinition of an alias that is also present in a different file 😭.
🔮 Other special characters and reserved words 🔮
The pound sign (‘#’) is used to indicate a comment (unless it is part of a #include directive or unless it occurs in the context of a user name and is followed by one or more digits, in which case it is treated as a user-ID). Both the comment character and any text after it, up to the end of the line, are ignored ✨.
The reserved word ALL is a built-in alias that always causes a match to succeed. It can be used wherever one might otherwise use a Cmnd_Alias, User_Alias, Runas_Alias, or Host_Alias. Attempting to define an alias named ALL will result in a syntax error 🙈.
big warning, bestie: using ALL can be dangerous since in a command context, it allows the user to run any command on the system 💀.
Okay so before we get to the flags, there's a word list you need to respect, bestie — because some names are already taken. 💅
The following option names permitted in an Option_Spec are also considered reserved words: CHROOT, ROLE, TYPE, TIMEOUT, CWD, NOTBEFORE and NOTAFTER. So like, if you try to define an alias with the same name as one of those options? Syntax error. Instantly. No vibe check, no grace period, just ✨error✨.
An exclamation point (!) can be used as a logical not operator in a list or alias as well as in front of a Cmnd. This is how you exclude certain values. The catch: for the ! operator to be effective, there has to be something for it to exclude. Like, it can't just yell "not!" into the void, it needs a friend to disagree with.
For example, to match all users except for root you'd write:
ALL, !rootBut if you drop the ALL,, like this:
!root…then it would explicitly deny root but not match any other users. That's a whole different creature from a true "negation" operator, iykyk. 🦋
Note, however, that using a!in conjunction with the built-inALLalias to allow a user to run "all but a few" commands rarely works as intended (see "SECURITY NOTES" below). So like… don't do the thing. Please. 😭
Long lines can be continued with a backslash (\) as the last character on the line — old-school but iconic. 🎀
White space between elements in a list, as well as the special syntactic characters in a User Specification (=, :, (, )), is optional. So breathe, you don't have to space everything perfectly.
The following characters must be escaped with a backslash (\) when used as part of a word (e.g., a user name or host name): !, =, :, ,, (, ), \. Yes, including the backslash itself. Escape your escapes. 🌀
✨ SUDOERS OPTIONS ✨
sudo's behavior can be modified by Default_Entry lines, as explained earlier (remember those?). A list of all supported Defaults parameters, grouped by type, are listed below. Grab a snack, this is a long one. 🍓
🎀 Boolean Flags 🎀
always_query_group_plugin— If agroup_pluginis configured, use it to resolve groups of the form%groupas long as there isn't also a system group of the same name. Normally, only groups of the form%:groupare passed to thegroup_plugin. This flag is off by default.always_set_home— If enabled, sudo will set theHOMEenvironment variable to the home directory of the target user (which is therunas_defaultuser unless the-uoption is used). This flag is largely obsolete and has no effect unless theenv_resetflag has been disabled orHOMEis present in theenv_keeplist — both of which are strongly discouraged. This flag is off by default.authenticate— If set, users must authenticate themselves via a password (or other means of authentication) before they may run commands. This default may be overridden via thePASSWDandNOPASSWDtags. This flag is on by default. 🔐case_insensitive_group— If enabled, group names in sudoers will be matched in a case insensitive manner. This may be necessary when users are stored in LDAP or AD. This flag is on by default.case_insensitive_user— If enabled, user names in sudoers will be matched in a case insensitive manner. This may be necessary when groups are stored in LDAP or AD. This flag is on by default.closefrom_override— If set, the user may use the-Coption, which overrides the default starting point at which sudo begins closing open file descriptors. This flag is off by default.compress_io— If set, and sudo is configured to log a command's input or output, the I/O logs will be compressed usingzlib. This flag is on by default when sudo is compiled withzlibsupport. 🗜️exec_background— By default, sudo runs a command as the foreground process as long as sudo itself is running in the foreground. When theexec_backgroundflag is enabled and the command is being run in a pseudo-terminal (due to I/O logging or theuse_ptyflag), the command will be run as a background process. Attempts to read from the controlling terminal (or to change terminal settings) will result in the command being suspended with theSIGTTINsignal (orSIGTTOUin the case of terminal settings). If this happens when sudo is a foreground process, the command will be granted the controlling terminal and resumed in the foreground with no user intervention required. The advantage of initially running the command in the background is that sudo need not read from the terminal unless the command explicitly requests it. Otherwise, any terminal input must be passed to the command, whether it has required it or not (the kernel buffers terminals so it is not possible to tell whether the command really wants the input). This is different from historic sudo behavior or when the command is not being run in a pseudo-terminal.
For this to work seamlessly, the operating system must support the automatic restarting of system calls. Unfortunately, not all operating systems do this by default, and even those that do may have bugs. For example, macOS fails to restart the tcgetattr(3) and tcsetattr(3) functions (this is a bug in macOS). Furthermore, because this behavior depends on the command stopping with the SIGTTIN or SIGTTOU signals, programs that catch these signals and suspend themselves with a different signal (usually SIGTOP) will not be automatically foregrounded. Some versions of the linux su(1) command behave this way. This flag is off by default.
This setting is only supported by version 1.8.7 or higher. It has no effect unless I/O logging is enabled or the use_pty flag is enabled. 🧚
env_editor— If set,visudowill use the value of theSUDO_EDITOR,VISUALorEDITORenvironment variables before falling back on the default editor list.visudois typically run as root, so this flag may allow a user withvisudoprivileges to run arbitrary commands as root without logging. 😬 An alternative is to place a colon-separated list of "safe" editors in theeditorsetting.visudowill then only useSUDO_EDITOR,VISUALorEDITORif they match a value specified ineditor. If theenv_resetflag is enabled, theSUDO_EDITOR,VISUALand/orEDITORenvironment variables must be present in theenv_keeplist for theenv_editorflag to function whenvisudois invoked via sudo. This flag is on by default.env_reset— If set, sudo will run the command in a minimal environment containing theTERM,PATH,HOME,MAIL,SHELL,LOGNAME,USERandSUDO_*variables. Any variables in the caller's environment or in the file specified by therestricted_env_filesetting that match theenv_keepandenv_checklists are then added, followed by any variables present in the file specified by theenv_filesetting (if any). The contents of theenv_keepandenv_checklists, as modified by globalDefaultsparameters in sudoers, are displayed when sudo is run by root with the-Voption. If thesecure_pathsetting is enabled, its value will be used for thePATHenvironment variable. This flag is on by default. 🌈fast_glob— Normally, sudo uses theglob(3)function to do shell-style globbing when matching path names. However, since it accesses the file system,glob(3)can take a long time to complete for some patterns, especially when the pattern references a network file system that is mounted on demand (auto mounted). Thefast_globflag causes sudo to use thefnmatch(3)function, which does not access the file system to do its matching. The disadvantage offast_globis that it is unable to match relative paths such as./lsor../bin/ls. This has security implications when path names that include globbing characters are used with the negation operator,!, as such rules can be trivially bypassed. As such, this flag should not be used when the sudoers file contains rules that contain negated path names which include globbing characters. This flag is off by default. 💀log_passwords— Most programs that require a user's password will disable echo before reading the password to avoid displaying the plaintext password on the screen. However, if terminal input is being logged (see "I/O LOGGING"), the password will still be present in the I/O log. If thelog_passwordsoption is disabled, sudoers will attempt to prevent passwords from being logged. It does this by using the regular expressions inpassprompt_regexto match a password prompt in the terminal output buffer. When a match is found, input characters in the I/O log will be replaced with*until either a line feed or carriage return is found in the terminal input or a new terminal output buffer is received. If, however, a program displays characters as the user types (such as sudo whenpwfeedbackis set), only the first character of the password will be replaced in the I/O log. This option has no effect unlesslog_inputorlog_ttyinare also set. This flag is on by default. 🙈fqdn— bestie, turn this on if you want fully qualified host names chillin' in the sudoers file whenever your local host name (the one thehostnamecommand hands you) is missing the domain part. So like, instead ofmyhostyou'd getmyhost.mydomain.edu. You can still use the short form if that's your vibe (mixing both is fine too, no cap). ⚠️ This flag only actually does anything when the "canonical" host name — the onegetaddrinfo(3)orgethostbyname(3)gives back — is already a fully-qualified domain name. That's usually what happens when the system is set up to use DNS for host name resolution.
Now, if your system hits up the /etc/hosts file before DNS, the "canonical" host name might not be fully-qualified at all. Which sources get queried, and in what order, is normally spelled out in /etc/nsswitch.conf, /etc/netsvc.conf, /etc/host.conf, or sometimes /etc/resolv.conf. And inside /etc/hosts, the first host name on the line is the one treated as the "canonical" name — everything after it is just aliases, and sudoers straight up ignores those. Like, this line for the machine xyzzy has the FQDN as the canonical name and the short one as an alias:
192.168.1.1 xyzzy.sudo.ws xyzzyIf that hosts file entry is formatted wrong, the fqdn flag won't do anything when it's queried before DNS. 😭
Also, huge heads-up: when you're using DNS for host name resolution, turning on fqdn makes sudoers do DNS lookups — which means if DNS stops working (say the machine gets disconnected from the network), sudo becomes literally unusable. 💀 And just like with the hosts file, you gotta use the "canonical" name exactly as DNS knows it. You may not use a host alias (CNAME entry) — partly for performance reasons, partly because there's genuinely no way to pull all the aliases out of DNS.
This flag is off by default.
ignore_audit_errors— lets commands run even when sudoers can't write to the audit log. Enabled = an audit log write failure is not treated as fatal. Disabled = a command only runs after the audit event has been written successfully. Only works on systems where sudoers actually supports audit logging, including FreeBSD, Linux, macOS, and Solaris. This flag is on by default. 🫶ignore_dot— if set, sudo will ignore"."or""(both of which mean the current directory) in thePATHenvironment variable. ThePATHitself does not get modified. This flag is on by default. 👑ignore_iolog_errors— lets commands run even if sudoers can't write to the I/O log (local or remote). Enabled = an I/O log write failure isn't fatal. Disabled = the command gets terminated if the I/O log can't be written to. This flag is off by default. 🙈ignore_logfile_errors— lets commands run even when sudoers can't write to the log file. Enabled = a log file write failure isn't treated as fatal. Disabled = a command only runs after the log file entry is successfully written. This only has any effect when sudoers is configured to use file-based logging via thelogfilesetting. This flag is on by default.ignore_local_sudoers— if this gets set via LDAP, parsing of/etc/sudoersis skipped entirely. It's made for sites that wanna block local sudoers files so that only LDAP is used, which thwarts rogue operators trying to sneak roles into/etc/sudoers. When this flag is enabled,/etc/sudoersdoesn't even need to exist. And since this flag tells sudo how to behave when no specific LDAP entries have been matched, this sudoOption is only meaningful for thecn=defaultssection. This flag is off by default.ignore_unknown_defaults— if set, sudo won't throw a warning when it runs into an unknownDefaultsentry in the sudoers file or an unknown sudoOption in LDAP. This flag is off by default.insults— if set, sudo will insult users when they type the wrong password. 😈 This flag is off by default.log_allowed— if set, sudoers logs commands allowed by the policy to the system audit log (where supported) plus syslog and/or a log file. This flag is on by default.
This setting is only supported by version 1.9.10 or higher.
log_denied— if set, sudoers logs commands denied by the policy to the system audit log (where supported) plus syslog and/or a log file. This flag is on by default.
This setting is only supported by version 1.8.29 or higher.
log_exit_status— if set, sudoers logs the exit value of commands that get run to syslog and/or a log file. And if a command was terminated by a signal, the signal name gets logged too. This flag is off by default.
This setting is only supported by version 1.9.8 or higher.
log_host— if set, the host name gets included in log entries written to the file configured by thelogfilesetting. This flag is off by default.log_input— if set, sudo runs the command in a pseudo-terminal (assuming sudo was run from a terminal) and logs all user input. And if standard input isn't connected to the user's terminal — because of I/O redirection, or because the command is part of a pipeline — that input gets logged too. Wanna know more about I/O logging? Peep the "I/O LOGGING" section. This flag is off by default. ✨log_output— if set, sudo runs the command in a pseudo-terminal (if sudo was run from a terminal) and logs all output sent to the user's terminal, the standard output, or the standard error. If stdout or stderr isn't connected to the user's terminal — I/O redirection, pipeline, you know the drill — that output is logged as well. More deets in the "I/O LOGGING" section. This flag is off by default.log_server_keepalive— if set, sudo turns on the TCP keepalive socket option on the connection to the log server, which means keepalive messages get sent to the server periodically. If the server doesn't respond to one of those messages, the connection gets closed and the running command gets terminated — unless theignore_iolog_errorsflag (I/O logging enabled) or theignore_log_errorsflag (I/O logging disabled) is set. This flag is on by default.
This setting is only supported by version 1.9.0 or higher.
log_server_verify— if set, the server certificate received during the TLS handshake has to be valid, and it must contain either the server name (fromlog_servers) or its IP address. If either condition isn't met, the TLS handshake fails. No negotiating. 💅 This flag is on by default.
This setting is only supported by version 1.9.0 or higher.
log_stderr— if set, sudo logs the standard error when it's not connected to the user's terminal. Useful for logging output headed to a pipe or redirected into a file. This flag is off by default, but it gets enabled whenever either thelog_outputflag or theLOG_OUTPUTcommand tag is set.log_stdin— if set, sudo logs the standard input when it's not connected to the user's terminal. Good for logging input coming from a pipe or redirected from a file. This flag is off by default, but it gets enabled whenever either thelog_inputflag or theLOG_INPUTcommand tag is set.log_stdout— if set, sudo logs the standard output when it's not connected to the user's terminal. Great for logging output headed to a pipe or redirected into a file. This flag is off by default, but it gets enabled whenever either thelog_outputflag or theLOG_OUTPUTcommand tag is set.log_subcmds— if set, sudoers logs when a command spawns a child process and runs a program using theexecve(2),execl(3),execle(3),execlp(3),execv(3),execvp(3),execvpe(3), orsystem(3)library functions. So like, if sudo runs a shell, every individual command run through that shell gets logged. This flag is off by default. 🔥
Lowkey the log_subcmds flag uses the same underlying mechanism as the intercept setting 😬 Some commands may not work properly when log_subcmds is enabled, due to the way it intercepts sub-commands. Peep the “Preventing shell escapes” section for more info on what systems support this option and its limitations. This setting is only supported by version 1.9.8 or higher and is incompatible with SELinux RBAC support unless the system supports seccomp(2) filter mode. 🫶
log_ttyin— bestie, if this is set,sudowill run the command in a pseudo-terminal and log user keystrokes sent to the user's terminal, if one is present 🎀 This flag is off by default but is enabled when either thelog_inputflag or theLOG_INPUTcommand tag is set. And if no terminal is present — like when you're running a remote command usingssh(1)— this flag will have no effect at all, so don't come for it 💅log_ttyout— if set,sudoruns the command in a pseudo-terminal and logs all output displayed on the user's terminal, if one is present ✨ This flag is off by default but gets enabled when either thelog_outputflag or theLOG_OUTPUTcommand tag is set. No terminal present (again: remote command viassh(1))? Then this flag has no effect, periodt 🌸log_year— if set, the four-digit year will be logged in the (non-syslog)sudolog file 🗓️ Off by default, iconically unbothered.long_otp_prompt— when validating with a One Time Password (OTP) scheme such as S/Key or OPIE, a two-line prompt is used to make it easier to cut and paste the challenge to a local window 🎀 It's not as pretty as the default but some people find it more convenient, and honestly? respect the workflow. This flag is off by default.mail_all_cmnds— send mail to themailtouser every single time a user attempts to run a command viasudo(this includessudoedit) 📬 No mail will be sent if the user runssudowith the-lor-voption unless there is an authentication error and themail_badpassflag is also set. This flag is off by default.mail_always— send mail to themailtouser every time a user runssudo💌 That's it, that's the whole vibe. Off by default.mail_badpass— send mail to themailtouser if the user runningsudodoes not enter the correct password 🙈 But heads up: if the command the user is attempting to run is not permitted bysudoersand one of themail_all_cmnds,mail_always,mail_no_host,mail_no_permsormail_no_userflags are set, this flag will have no effect. This flag is off by default.mail_no_host— if set, mail will be sent to themailtouser if the invoking user exists in thesudoersfile, but is not allowed to run commands on the current host 😭 Off by default.mail_no_perms— if set, mail will be sent to themailtouser if the invoking user is allowed to usesudobut the command they are trying is not listed in theirsudoersfile entry or is explicitly denied 💀 Off by default.mail_no_user— if set, mail will be sent to themailtouser if the invoking user is not in thesudoersfile ✉️ And plot twist: this flag is on by default 👑match_group_by_gid— okay so by default,sudoerswill look up each group the user is a member of by group-ID to determine the group name (this is only done once). The resulting list of the user's group names is used when matching groups listed in thesudoersfile 🦋 This works well on systems where the number of groups listed in thesudoersfile is larger than the number of groups a typical user belongs to. But on systems where group lookups are slow, where users may belong to a large number of groups, or where the number of groups listed in thesudoersfile is relatively small, it may be prohibitively expensive and running commands viasudomay take longer than normal 😭 On such systems it may be faster to use thematch_group_by_gidflag to avoid resolving the user's group-IDs to group names. In this case,sudoersmust look up any group name listed in thesudoersfile and use the group-ID instead of the group name when determining whether the user is a member of the group.
If match_group_by_gid is enabled, group database lookups performed by sudoers will be keyed by group name as opposed to group-ID 👀 On systems where there are multiple sources for the group database, it is possible to have conflicting group names or group-IDs in the local /etc/group file and the remote group database. On such systems, enabling or disabling match_group_by_gid can be used to choose whether group database queries are performed by name (enabled) or ID (disabled), which may aid in working around group entry conflicts. iykyk 🧚
The match_group_by_gid flag has no effect when sudoers data is stored in LDAP. This flag is off by default.
This setting is only supported by version 1.8.18 or higher.
intercept— if set, all commands run viasudowill behave as if theINTERCEPTtag has been set, unless overridden by anNOINTERCEPTtag 🔥 Some commands may not work properly wheninterceptis enabled, due to the way it intercepts sub-commands — see the description ofINTERCEPTandNOINTERCEPTabove as well as the “Preventing shell escapes” section at the end of this manual, bestie. This flag is off by default.
This setting is only supported by version 1.9.8 or higher and is incompatible with SELinux RBAC support unless the system supports seccomp(2) filter mode.
intercept_allow_setid— on most systems, the dynamic loader will ignoreLD_PRELOAD(or the equivalent) when running set-user-ID and set-group-ID programs, effectively disabling intercept mode 😬 To prevent this from happening,sudoerswill not permit a set-user-ID or set-group-ID program to be run in intercept mode unlessintercept_allow_setidis enable. This flag has no effect unless theinterceptflag is enabled or theINTERCEPTtag has been set for the command. This flag is on by default when theintercept_typeoption is set totrace, otherwise it default to off 💅
This setting is only supported by version 1.9.8 or higher.
intercept_authenticate— if set, commands run by an intercepted process must be authenticated when the user's time stamp is not current 🕐 For example, if a shell is run withinterceptenabled, as soon as the invoking user's time stamp is out of date, subsequent commands will need to be authenticated. This flag has no effect unless theinterceptflag is enabled or theINTERCEPTtag has been set for the command. This flag is off by default.
This setting is only supported by version 1.9.8 or higher.
intercept_verify— if set,sudowill attempt to verify that a command run in intercept mode has the expected path name, command line arguments and environment 🔍✨
The process will be stopped after execve(2) has completed but before the new command has had a chance to run. To verify the command, sudo will read the command's path from /proc/PID/exe, the command line arguments and environment from the process's memory, and compare them against the arguments that were passed to execve(2). In the event of a mismatch, the command will be sent a SIGKILL signal and terminated 💀 no cap.
This can help prevent a time of check versus time of use issue with intercept mode where the execve(2) arguments could be altered after the sudoers policy check. The checks can only be performed if the proc(5) file system is available. This flag has no effect unless the intercept flag is enabled or the INTERCEPT tag has been set for the command and the intercept_type option is set to trace.
This setting is incompatible with programs that change their root directory viachroot(2). If a program changes its root directory, path names will no longer match those seen by thesudoparent process and sub-commands will be terminated before they have a chance to run 😭
This flag is on by default.
This setting is only supported by version 1.9.12 or higher.
netgroup_tuple— if set, netgroup lookups will be performed using the full netgroup tuple: host name, user name, and domain (if one is set) 🌈 Historically,sudoonly matched the user name and domain for netgroups used in a User_List and only matched the host name and domain for netgroups used in a Host_List. This flag is off by default.noexec— flip this on and every single command run throughsudobehaves like theNOEXECtag got set, unless anEXECtag overrides it. Go peep theEXEC/NOEXECdescriptions above, plus the “Preventing shell escapes” section at the very end of this manual. This flag is off by default. 💅noninteractive_auth— okay so with this set, authentication gets attempted even in non-interactive mode (that's when you pass sudo's-noption). The point? It lets auth methods that don't need the user to do anything succeed. Auth methods that do need input from the user's terminal will still fail, periodt. If you disable it, no authentication is attempted at all in non-interactive mode. This flag is off by default.
This setting is only supported by version 1.9.10 or higher. ✨
pam_acct_mgmt— on systems that use PAM for authentication,sudoperforms PAM account validation for the invoking user by default. What actually gets checked depends on which PAM modules you've got configured. If enabled, account validation happens regardless of whether a password is required. This flag is on by default. 🫶
This setting is only supported by version 1.8.28 or higher.
pam_rhost— on PAM systems, when thepam_rhostflag is enabled,sudosets the PAM remote host value to the name of the local host. Heads up on Linux: enablingpam_rhostmay result in DNS lookups of the local host name when PAM is initialized. And on Solaris versions prior to Solaris 8,pam_rhostmust be enabled ifpam_ruseris also enabled, otherwise you get a crash in the Solaris PAM implementation. 😭 This flag is off by default on systems other than Solaris.
This setting is only supported by version 1.9.0 or higher.
pam_ruser— on PAM systems, when thepam_ruserflag is enabled,sudosets the PAM remote user value to the name of the user that invokedsudo. That's it, that's the vibe. This flag is on by default. 🌸
This setting is only supported by version 1.9.0 or higher.
pam_session— on PAM systems,sudocreates a brand-new PAM session for the command to run in. Unlesssudois given the-ior-soptions, PAM session modules are run with the “silent” flag enabled — which keeps last login information from being displayed for every single command on some systems. Iconic. 🎀 Disablingpam_sessionmay be needed on older PAM implementations, or on operating systems where opening a PAM session changes theutmporwtmpfiles. But real talk: if PAM session support is disabled, resource limits may not be updated for the command being run. Also — ifpam_session,pam_setcred, anduse_ptyare all disabled,log_servershas not been set, and I/O logging has not been configured,sudowill execute the command directly instead of running it as a child process. This flag is on by default.
This setting is only supported by version 1.8.7 or higher.
pam_setcred— on PAM systems,sudoattempts to establish credentials for the target user by default, if the underlying authentication system supports it. One example of a credential is a Kerberos ticket. 🎫 Same deal as above: ifpam_session,pam_setcred, anduse_ptyare all disabled,log_servershas not been set, and I/O logging has not been configured,sudoexecutes the command directly instead of running it as a child process. This flag is on by default.
This setting is only supported by version 1.8.8 or higher.
pam_silent— if set, PAM authentication happens in silent mode, which stops PAM authentication modules from generating output. Lowkey a double-edged sword though: in some cases this may suppress important info about why authentication failed. For example, PAM modules such aspam_faillockwill only display a warning ifpam_silentis disabled. This flag is on by default. 💜
This setting is only supported by version 1.9.16 or higher.
passprompt_override— if set, the prompt specified bypasspromptor theSUDO_PROMPTenvironment variable is always used, and it replaces whatever prompt a PAM module or other authentication method hands you. No competing prompts, no confusion, main character prompt energy only. This flag is off by default.path_info— normally,sudotells the user when a command couldn't be found in theirPATHenvironment variable. Some sites may want to disable this, since it could be used to gather information on the location of executables that the normal user doesn't have access to. The downside? If the executable is simply not in the user'sPATH,sudowill tell the user that they're not allowed to run it, which can be confusing. 🙈 This flag is on by default.preserve_groups— by default,sudoinitializes the group vector to the list of groups the target user is in. Whenpreserve_groupsis set, the user's existing group vector is left unaltered. The real and effective group-IDs, however, are still set to match the target user. This flag is off by default.pwfeedback— by default,sudoreads the password like most other Unix programs do: echo stays off until the user hits the return (or enter) key. Some users get confused by this because it looks likesudohas hung at that point. Whenpwfeedbackis set,sudogives visual feedback when the user presses a key. But — this does have a security impact, because an onlooker may be able to determine the length of the password being entered. 👀 This flag is off by default.requiretty— if set,sudoonly runs when the user is logged in to a real tty. With this flag set,sudocan only be run from a login session — not via other means such ascron(8)or cgi-bin scripts. This flag is off by default.root_sudo— if set, root is allowed to runsudotoo. Disabling this prevents users from “chaining”sudocommands to get a root shell by doing something like ‘sudo sudo /bin/sh’. Note, however, that turning offroot_sudowill also prevent root from runningsudoedit. And ngl, disablingroot_sudoprovides no real additional security — it exists purely for historical reasons. This flag is on by default. 👑rootpw— if set,sudoprompts for the root password instead of the password of the invoking user when running a command or editing a file. This flag is off by default.runas_allow_unknown_id— if enabled, this allows matching of runas user and group IDs that are not present in the password or group databases. Beyond explicitly matching unknown user or group IDs in aRunas_List, this option also lets theALLalias match unknown IDs. This flag is off by default.
This setting is only supported by version 1.8.30 or higher. Older versions of sudo always allowed matching of unknown user and group IDs.
runas_check_shell— if enabled,sudowill only run commands as a user whose shell appears in the/etc/shellsfile, even if the invoking user'sRunas_Listwould otherwise permit it. If no/etc/shellsfile is present, a system-dependent list of built-in default shells gets used. On many operating systems, system users such as “bin” don't have a valid shell, and this flag is exactly how you stop commands from being run as those users. 🐚 This flag is off by default.
This setting is only supported by version 1.8.30 or higher.
runaspw— if set,sudoprompts for the password of the user defined by therunas_defaultoption (which defaults toroot) instead of the password of the invoking user when running a command or editing a file. This flag is off by default.selinux— if enabled, the user may specify an SELinux role and/or type to use when running the command, as permitted by the SELinux policy. If SELinux is disabled on the system, this flag has no effect. This flag is on by default. 🌈set_home— if enabled andsudois invoked with the-soption, theHOMEenvironment variable gets set to the home directory of the target user (which is therunas_defaultuser unless the-uoption is used). Big caveat: this flag is largely obsolete and has no effect unless theenv_resetflag has been disabled orHOMEis present in theenv_keeplist — both of which are strongly discouraged. This flag is off by default. 💀set_logname— okay so normallysudosets theLOGNAMEandUSERenvironment variables to the name of the target user (that's the user specified byrunas_default, unless you pass-u, bestie). But here's the thing: some programs (yes, including the RCS revision control system, iconic throwback) useLOGNAMEto figure out who the real user is 👀 — so you might want to change this behavior. You do that by negating theset_lognameoption. Heads up though:set_lognamewill have no effect if theenv_resetoption has not been disabled and theenv_keeplist containsLOGNAMEorUSER. This flag is on by default.set_utmp— when this is enabled,sudocreates an entry in theutmp(orutmpx) file whenever a pseudo-terminal is allocated 🎀. And when doessudoallocate a pseudo-terminal? When it's running in a terminal and one or more of thelog_input,log_output,log_stdin,log_stdout,log_stderr,log_ttyin,log_ttyout, oruse_ptyflags is enabled. By default the new entry is a copy of the user's existingutmpentry (if there is one), with thetty,time,type, andpidfields updated. This flag is on by default.setenv— lets the user disable theenv_resetoption from the command line via the-Eoption 🫶. Bonus: environment variables set via the command line are not subject to the restrictions imposed byenv_check,env_delete, orenv_keep. Which is exactly why only trusted users should be allowed to set variables in this manner. This flag is off by default.shell_noargs— if this is set andsudois invoked with no arguments, it acts as if the-soption had been given ✨. Basically it runs a shell as root — and the shell is determined by theSHELLenvironment variable if it's set, falling back on the shell listed in the invoking user's/etc/passwdentry if not. This flag is off by default.stay_setuid— normally, whensudoexecutes a command, the real and effective user-IDs both get set to the target user (root by default). This option changes that up so the real user-ID is left as the invoking user's user-ID. In other words, it makessudoact as a set-user-ID wrapper 💅. This can be useful on systems that disable some potentially dangerous functionality when a program is run set-user-ID. Caveat though: this option is only effective on systems that support either thesetreuid(2)orsetresuid(2)system call. This flag is off by default.sudoedit_checkdir— if set,sudoeditwill check all directory components of the path to be edited for writability by the invoking user 🔥. Symbolic links will not be followed in writable directories, andsudoeditwill refuse to edit a file located in a writable directory. These restrictions are not enforced whensudoeditis run by root. Also, on some systems, if all directory components of the path to be edited are not readable by the target user,sudoeditwill be unable to edit the file. This flag is on by default.
This setting was first introduced in version 1.8.15 but initially suffered from a race condition 😭 — the check for symbolic links in writable intermediate directories was added in version 1.8.16.
sudoedit_follow— by default,sudoeditwill not follow symbolic links when opening files. Thesudoedit_followoption can be enabled to allowsudoeditto open symbolic links 🦋. It may be overridden on a per-command basis by theFOLLOWandNOFOLLOWtags. This flag is off by default.
This setting is only supported by version 1.8.15 or higher.
syslog_pid— when logging viasyslog(3), include the process ID in the log entry 🌸. This flag is off by default.
This setting is only supported by version 1.8.21 or higher.
targetpw— if set,sudowill prompt for the password of the user specified by the-uoption (defaults to the value ofrunas_default) instead of the password of the invoking user when running a command or editing a file 👑. Note that this flag precludes the use of a user-ID not listed in the passwd database as an argument to the-uoption. This flag is off by default.tty_tickets— if set, users must authenticate on a per-tty basis 💜. With this flag enabled,sudowill use a separate record in the time stamp file for each terminal. If disabled, a single record is used for all login sessions.
Heads up: this option has been superseded by the timestamp_type option.
umask_override— if set,sudowill set the umask as specified in thesudoersfile without modification 😌. This makes it possible to specify a umask in thesudoersfile that is more permissive than the user's own umask, and matches historical behavior. Ifumask_overrideis not set,sudowill set the umask to be the union of the user's umask and what is specified insudoers. This flag is off by default.use_netgroups— if set, netgroups (prefixed with+) may be used in place of a user or host 🌈. For LDAP-basedsudoers, netgroup support requires an expensive sub-string match on the server unless theNETGROUP_BASEdirective is present in the/etc/sudo-ldap.conffile. If netgroups are not needed, this option can be disabled to reduce the load on the LDAP server. This flag is on by default.use_pty— if set, andsudois running in a terminal, the command will be run in a new pseudo-terminal 🎀. If thesudoprocess is not attached to a terminal,use_ptyhas no effect.
Why do you care? Because a malicious program run under sudo may be capable of injecting commands into the user's terminal, or running a background process that retains access to the user's terminal device even after the main program has finished executing 💀. By running the command in a separate pseudo-terminal, this attack is no longer possible. Slay.
One side effect of running the command in a new pseudo-terminal is that input will be passed to the command even if it is non-interactive. So, for example, keys pressed while a non-interactive command is running will be consumed by sudo instead of being passed to the shell after the command exits 🙈.
This flag is on by default for sudo 1.9.14 and above.
user_command_timeouts— if set, the user may specify a timeout on the command line ⏳. If the timeout expires before the command has exited, the command will be terminated. If a timeout is specified both in thesudoersfile and on the command line, the smaller of the two timeouts will be used. See the Timeout_Spec section for a description of the timeout syntax. This flag is off by default.
This setting is only supported by version 1.8.20 or higher.
utmp_runas— if set,sudowill store the name of the runas user when updating theutmp(orutmpx) file 🌟. By default,sudostores the name of the invoking user. This flag is off by default.visiblepw— by default,sudowill refuse to run if the user must enter a password but it is not possible to disable echo on the terminal 🙅. If thevisiblepwflag is set,sudowill prompt for a password even when it would be visible on the screen 👀. This makes it possible to run things likessh somehost sudo ls, since by defaultssh(1)does not allocate a tty when running a command. This flag is off by default.
Integers:
closefrom— before it executes a command,sudowill close all open file descriptors other than standard input, standard output, and standard error (file descriptors0–2) 🧚. Theclosefromoption can be used to specify a different file descriptor at which to start closing. The default is3.command_timeout— the maximum amount of time a command is allowed to run before it is terminated ⏰. See the Timeout_Spec section for a description of the timeout syntax.
This setting is only supported by version 1.8.20 or higher.
log_server_timeout— the maximum amount of time to wait when connecting to a log server or waiting for a server response 📡. See the Timeout_Spec section for a description of the timeout syntax. The default value is30seconds.
This setting is only supported by version 1.9.0 or higher.
✨ maxseq — okay so this is the max sequence number that gets substituted for the %{seq} escape in the I/O log file (peep the iolog_dir description below for more on that). The value that gets substituted for %{seq} is in base 36, but maxseq itself should be written in decimal. Values bigger than 2176782336 (which is the base 36 sequence number ZZZZZZ) get silently truncated to 2176782336. The default value is 2176782336.
Once the local sequence number hits the value of maxseq, it will “roll over” to zero, and after that sudoers will truncate and reuse any existing I/O log path names. This setting is only supported by version 1.8.7 or higher. 🌀
passwd_tries— the number of tries a user gets to enter their password beforesudologs the failure and exits. The default is3. 🔐syslog_maxlen— on many systems,syslog(3)has a relatively small log buffer. IETF RFC 5424 states that syslog servers must support messages of at least480bytes and should support messages up to2048bytes. By default,sudoerscreates log messages up to980bytes, which corresponds to the historic BSD syslog implementation that used a1024byte buffer to store the message, date, hostname, and program name. To prevent syslog messages from being truncated,sudoerswill split up log messages that are larger thansyslog_maxlenbytes. When a message is split, the additional parts will include the string(command continued)after the user name and before the continued command line arguments. This setting is only supported by version1.8.19or higher. 📜
✨ Integers that can be used in a boolean context ✨
loglinelen— number of characters per line for the file log. This value is used to decide when to wrap lines for nicer log files. It has no effect on the syslog log file, only the file log. The default is80(use0or negate the option to disable word wrap). 📏passwd_timeout— number of minutes before thesudopassword prompt times out, or0for no timeout. The timeout may include a fractional component if minute granularity is insufficient, for example2.5. The default is5. ⏳timestamp_timeout— number of minutes that can elapse beforesudowill ask for a password again. The timeout may include a fractional component if minute granularity is insufficient, for example2.5. The default is5. Set this to0to always prompt for a password. If set to a value less than0, the user's time stamp will not expire until the system is rebooted. This can be used to allow users to create or delete their own time stamps viasudo -vandsudo -krespectively. 🕰️umask— file mode creation mask to use when running the command. Negate this option or set it to0777to preventsudoersfrom changing the umask. Unless theumask_overrideflag is set, the actual umask will be the union of the user's umask and the value of theumasksetting, which defaults to0022. This guarantees thatsudonever lowers the umask when running a command.
If umask is explicitly set in sudoers, it will override any umask setting in PAM or login.conf. If umask is not set in sudoers, the umask specified by PAM or login.conf will take precedence. The umask setting in PAM is not used for sudoedit, which does not create a new PAM session. 🎭
🎀 Strings 🎀
cmddenial_message— when it's set,sudowill display this message when a user is denied access to run the specified command, but is listed in thesudoersfile for the host. This can be used to provide additional, site-specific information to the user when a command is denied by the security policy. It does not override the standard warning the user receives when a command is denied. 🚫authfail_message— message that is displayed after a user fails to authenticate. The message may include the%descape, which will expand to the number of failed password attempts. If set, it overrides the default message,%d incorrect password attempt(s). 😭badpass_message— message that is displayed if a user enters an incorrect password. The default isSorry, try again.unlessinsultsare enabled. 🙈editor— a colon (:) separated list of editor path names used bysudoeditandvisudo. Forsudoedit, this list is used to find an editor when none of theSUDO_EDITOR,VISUALorEDITORenvironment variables are set to an editor that exists and is executable. Forvisudo, it is used as a white list of allowed editors;visudowill choose the editor that matches the user'sSUDO_EDITOR,VISUALorEDITORenvironment variable if possible, or the first editor in the list that exists and is executable if not. Unless invoked assudoedit,sudodoes not preserve theSUDO_EDITOR,VISUALorEDITORenvironment variables unless they are present in theenv_keeplist or theenv_resetoption is disabled. The default is/bin/vi. ✍️intercept_type— the underlying mechanism used by theinterceptandlog_subcmdsoptions. It has the following possible values:dso— preload a dynamic shared object (shared library) that intercepts theexecve(2),execl(3),execle(3),execlp(3),execv(3),execvp(3),execvpe(3), andsystem(3)library functions. A value ofdsois incompatible with sudo's SELinux RBAC support. 🧩trace— useptrace(2)to intercept theexecve(2)system call. This is only supported on Linux systems whereseccomp(2)filtering is enabled. If the/proc/sys/kernel/seccomp/actions_availfile is missing or does not contain atrapelement, settingintercept_typetotracewill have no effect anddsowill be used instead. 🕵️♀️
The default is to use trace if it is supported by the system and dso if it is not. ⚙️
iolog_dir— the top-level directory to use when constructing the path name for the input/output log directory. Only used if thelog_inputorlog_outputoptions are enabled or when theLOG_INPUTorLOG_OUTPUTtags are present for a command. The session sequence number, if any, is stored in the directory. The default is/var/log/sudo-io. 📁
The following percent (%) escape sequences are supported:
%{seq}— expanded to a monotonically increasing base-36 sequence number, such as0100A5, where every two digits are used to form a new directory, e.g.,01/00/A5🔢%{user}— expanded to the invoking user's login name 👤%{group}— expanded to the name of the invoking user's real group-ID 👥%{runas_user}— expanded to the login name of the user the command will be run as (e.g.,root) 👑%{runas_group}— expanded to the group name of the user the command will be run as (e.g.,wheel) 🎡%{hostname}— expanded to the local host name without the domain name 🖥️%{command}— expanded to the base name of the command being run 🏃♀️
In addition, any escape sequences supported by the system's strftime(3) function will be expanded. To include a literal % character, the string %% should be used. Any path name separator characters (/) present in the user, group or host name will be replaced with an underbar (_) during expansion. 🌸
iolog_file— the path name, relative toiolog_dir, in which to store input/output logs when thelog_inputorlog_outputoptions are enabled or when theLOG_INPUTorLOG_OUTPUTtags are present for a command.iolog_filemay contain directory components. The default is%{seq}. See theiolog_diroption above for a list of supported percent (%) escape sequences. 📝
In addition to the escape sequences, path names that end in six or more Xs will have the Xs replaced with a unique combination of digits and letters, similar to the mktemp(3) function. If the path created by concatenating iolog_dir and iolog_file already exists, the existing I/O log file will be truncated and overwritten unless iolog_file ends in six or more Xs. 💀
iolog_flush— okay so when this is on,sudoflushes the I/O log data straight to disk after every single write instead of buffering it 💾. The glow-up here is that you can peek at the logs in real-time while the program is still running 👀 — but the trade-off is real: it may significantly reduce the effectiveness of I/O log compression. This flag is off by default.
Only supported by version 1.8.20 or higher, bestie 🫶.
iolog_group— the group namesudolooks up when it sets the group-ID on brand-new I/O log files and directories 👑. Ifiolog_groupisn't set, it uses the primary group-ID of the user named byiolog_userinstead. And if neitheriolog_groupnoriolog_useris set, I/O log files and directories get created with group-ID 0.
Only supported by version 1.8.19 or higher ✨.
iolog_mode— the file mode to use when creating I/O log files 🎀. The read and write permission bits for owner, group, or other are honored; everything else is ignored. The file permissions will always include the owner read and write bits, even if they're not present in the mode you specified (rude of you to try, but okay). When creating I/O log directories, search (execute) bits get added to match the read and write bits specified byiolog_mode. Defaults to0600(read and write by user only).
Only supported by version 1.8.19 or higher 💅.
iolog_user— the user name to look up when setting the user and group-IDs on new I/O log files and directories 🦋. Ifiolog_groupis set, it gets used instead of this user's primary group-ID. By default, I/O log files and directories are created with user and group-ID 0.
This one is genuinely useful when your I/O logs live on a Network File System (NFS) share — having a dedicated user own the I/O log files means sudoers doesn't write to the log files as user-ID 0, which is usually not permitted by NFS 🫠.
Only supported by version 1.8.19 or higher 🌸.
lecture_status_dir— the directory wheresudostashes its per-user lecture status files 📚. Once a user has received the lecture (you know the one), a zero-length file gets created in this directory sosudowon't lecture them again. Heads up: this directory should not be cleared when the system reboots ⚠️. The default is/var/db/sudo/lectured.log_server_cabundle— the path to a certificate authority bundle file, in PEM format, to use instead of the system's default certificate authority database when authenticating the log server 🔐. The default is to use the system's default certificate authority database. Ngl, this setting has no effect unlesslog_serversis set and the remote log server is secured with TLS.
Only supported by version 1.9.0 or higher ✨.
log_server_peer_cert— the path to thesudoclient's certificate file, in PEM format 🪪. This setting is required when the remote log server is secured with TLS and client certificate validation is enabled. Forsudo_logsrvd, client certificate validation is controlled by thetls_checkpeeroption, which defaults tofalse.
Only supported by version 1.9.0 or higher 🎀.
log_server_peer_key— the path to thesudoclient's private key file, in PEM format 🔑. This setting is required when the remote log server is secured with TLS and client certificate validation is enabled. Forsudo_logsrvd, client certificate validation is controlled by thetls_checkpeerflag, which defaults tofalse.
Only supported by version 1.9.0 or higher 💜.
mailsub— the subject line of the mail sent to themailtouser 📧. The escape%hexpands to the host name of the machine. Default is*** SECURITY information for %h ***.noexec_file— yeah so as ofsudoversion 1.8.1 this option is no longer supported 💀. The path to the noexec file should now be set in thesudo.conf(5)file instead. Rip to a real one.pam_askpass_service— on systems that use PAM for authentication, this is the service name used when the-Aoption is specified 🧚. The default value is eithersudoorsudo-i, depending on whether or not the-ioption is also specified. See the description ofpam_servicefor more info.
Only supported by version 1.9.9 or higher ⭐.
pam_login_service— on systems that use PAM for authentication, this is the service name used when the-ioption is specified 🌈. The default value issudo-i. See the description ofpam_servicefor more info.
Only supported by version 1.8.8 or higher ✨.
pam_service— on systems that use PAM for authentication, the service name specifies the PAM policy to apply 🛂. This usually corresponds to an entry in thepam.conffile or a file in the/etc/pam.ddirectory. The default value issudo.
Only supported by version 1.8.8 or higher 🌸.
passprompt— the default prompt to use when asking for a password 🗣️; it can be overridden via the-poption or theSUDO_PROMPTenvironment variable. The following percent (%) escape sequences are supported:%H— expanded to the local host name including the domain name (only if the machine's host name is fully qualified or thefqdnoption is set).%h— expanded to the local host name without the domain name.%p— expanded to the user whose password is being asked for (respects therootpw,targetpwandrunaspwflags insudoers).%U— expanded to the login name of the user the command will be run as (defaults toroot).%u— expanded to the invoking user's login name.%%— two consecutive%characters are collapsed into a single%character.
On systems that use PAM for authentication, passprompt will only be used if the prompt provided by the PAM module matches the string Password: or username's Password: 🫶. This ensures that the passprompt setting does not interfere with challenge-response style authentication — very considerate of it, honestly. The passprompt_override flag can be used to change this behavior.
The default value is [sudo] password for %p: .
role— the default SELinux role to use when constructing a new security context to run the command 🎭. The default role may be overridden on a per-command basis in thesudoersfile or via command line options. This option is only available whensudois built with SELinux support — no SELinux, no role, sorry babe.runas_default— the default user to run commands as if the-uoption isn't specified on the command line 👤. This defaults toroot.sudoers_locale— the locale to use when parsing thesudoersfile, logging commands, and sending email 🌍. Careful though: changing the locale may affect howsudoersis interpreted 😭. Defaults toC.timestamp_type— sosudoersuses per-user time stamp files for credential caching ⏰. Thetimestamp_typeoption lets you specify which type of time stamp record gets used. It has the following possible values:global— a single time stamp record is used for all of a user's login sessions, regardless of the terminal or parent process ID. An additional record is used to serialize password prompts whensudois used multiple times in a pipeline, but this does not affect authentication.ppid— a single time stamp record is used for all processes with the same parent process ID (usually the shell). Commands run from the same shell (or other common parent process) won't require a password fortimestamp_timeoutminutes (5 by default). Commands run viasudowith a different parent process ID — for example from a shell script — will be authenticated separately.tty— one time stamp record is used for each terminal, which means a user's login sessions are authenticated separately. If no terminal is present, the behavior is the same asppid. Commands run from the same terminal won't require a password fortimestamp_timeoutminutes (5 by default).
kernel— the time stamp lives in the kernel, stored as an attribute of the terminal device itself 🖥️. No terminal around? Then it behaves exactly likeppid. Quick warning though: negativetimestamp_timeoutvalues are not supported here, and positive values max out at 60 minutes 🕐. Currently only supported on OpenBSD. The default value istty. This setting is only supported by version 1.8.21 or higher.timestampdir— the directory where sudo keeps its time stamp files 📁. This directory should be cleared when the system reboots (yes, should — it's giving housekeeping energy 🧹). Default is/run/sudo/ts.timestampowner— the owner of the lecture status directory, the time stamp directory, and all the files stored inside them 👑. Default isroot.type— the default SELinux type to use when constructing a new security context to run the command 🛡️. Ngl, the default type can be overridden on a per-command basis in the sudoers file, or via command line options. Heads up: this option is only available when sudo is built with SELinux support 💅.
🔮 Strings that can be used in a boolean context
admin_flag— specifies the path to a file that gets created the first time a user who's a member of thesudooradmingroups runs sudo 🎀. Only available if sudo is configured with the--enable-admin-flagoption. The default value is~/.sudo_as_admin_successful.env_file— specifies the fully qualified path to a file containing variables to be set in the environment of the program being run 🌱. Entries in this file should either be of the formVARIABLE=valueorexport VARIABLE=value. The value may optionally be enclosed in single or double quotes. Variables in this file are only added if the variable does not already exist in the environment. Big deal: this file is considered to be part of the security policy, so its contents are not subject to other sudo environment restrictions likeenv_keepandenv_check🔥.exempt_group— users in this group are exempt from password andPATHrequirements 🙌. The group name you specify should not include a%prefix. This is not set by default.fdexec— determines whether sudo will execute a command by its path or by an open file descriptor 🗂️. It has the following possible values:always— always execute by file descriptor.never— never execute by file descriptor.digest_only— only execute by file descriptor if the command has an associated digest in the sudoers file.
The default value is digest_only. This avoids a time of check versus time of use race condition when the command is located in a directory writable by the invoking user 😱 — yes, that's the scary kind, we love that it's handled.
Heads up bestie, fdexec will change the first element of the argument vector for scripts ($0 in the shell), because of the way the kernel runs script interpreters. Instead of being a normal path, it'll refer to a file descriptor. For example, /dev/fd/4 on Solaris and /proc/self/fd/4 on Linux 🌀. A workaround is to use the SUDO_COMMAND environment variable instead.
Also: the fdexec setting is only used when the command is matched by path name. It has no effect if the command is matched by the built-in ALL alias. This setting is only supported by version 1.8.20 or higher. And if the operating system doesn't support the fexecve(2) system call, this setting has no effect 💀.
group_plugin— a string containing a sudoers group plugin with optional arguments 🔌. The string should consist of the plugin path — either fully-qualified or relative to the/usr/libexec/sudodirectory — followed by any configuration arguments the plugin requires. These arguments (if any) will be passed to the plugin's initialization function. If arguments are present, the string must be enclosed in double quotes ("").
On 64-bit systems, if the plugin is present but can't be loaded, sudoers will look for a 64-bit version and, if it exists, load that as a fallback 🪄. The exact rules for this vary by system:
- On Solaris, if the plugin is stored in a directory ending in “lib”, sudoers will create a fallback path by appending “/64” to the directory name;
/usr/lib/group_plugin.sobecomes/usr/lib/64/group_plugin.so. - On Linux, a directory ending in “lib” will be transformed to “lib64” as the fallback path;
/usr/lib/group_plugin.sobecomes/usr/lib64/group_plugin.so. - On all other systems, the fallback path is generated by adding a “64” before the file extension;
group_plugin.sobecomesgroup_plugin64.so.
On AIX systems, the plugin may be either a shared object ending in .so or an archive file containing a shared object ending in .a with the name of the shared object in parentheses at the end 📦.
For more info, see “GROUP PROVIDER PLUGINS” 👀.
lecture— controls when a short lecture gets printed along with the password prompt 📢. It has the following possible values:always— always lecture the user.never— never lecture the user.once— only lecture the user the first time they run sudo.
If no value is specified, a value of once is implied. Negating the option results in a value of never being used. The default value is once.
lecture_file— path to a file containing an alternate sudo lecture that'll be used in place of the standard lecture if the named file exists 📜. By default, sudo uses a built-in lecture.listpw— controls when a password will be required when a user runs sudo with the-loption 🔐. It has the following possible values:all— all the user's sudoers file entries for the current host must have theNOPASSWDflag set to avoid entering a password.always— the user must always enter a password to use the-loption.any— at least one of the user's sudoers file entries for the current host must have theNOPASSWDflag set to avoid entering a password.never— the user need never enter a password to use the-loption.
If no value is specified, a value of any is implied. Negating the option results in a value of never being used. The default value is any.
log_format— the event log format 📊. Supported log formats are:json— currently, this is an alias forjson_pretty. In a future version of sudo,jsonwill be equivalent tojson_compact. JSON log entries contain the full user details as well as the execution environment if the command was allowed.json_compact— log events in “compact” (minified) JSON format. Each event is written as a separate JSON object on a single line without extraneous white space. Due to limitations of the protocol, JSON events sent via syslog may be truncated ⚠️.json_pretty— log events in “pretty” JSON format. When logging to a file, the entire file is treated as a single JSON object consisting of multiple events, each event spanning multiple lines. When logging via syslog, there is no difference between thejson_prettyandjson_compactformats.sudo— log events in traditional sudo-style format, see “EVENT LOGGING” for details.
This setting affects logs sent via syslog(3) as well as the file specified by the logfile setting, if any. The default value is sudo.
logfile— path to the sudo log file (not the syslog log file) 📝. Setting a path turns on logging to a file; negating this option turns it off. By default, sudo logs via syslog.mailerflags— flags to use when invokingmailer📬. Defaults to-t.mailerpath— path to the mail program used to send warning mail (negate to prevent sudo from sending mail). Defaults to the path tosendmailfound at configure time.mailfrom— address to use for the “from” address when sending warning and error mail 💌. The address should be enclosed in double quotes ("") to protect against sudo interpreting the@sign. Defaults to the name of the user running sudo.mailto— address to send warning and error mail to (negate to prevent sudo from sending mail). The address should be enclosed in double quotes ("") to protect against sudo interpreting the@sign. Defaults toroot.rlimit_as— the maximum size to which the process's address space may grow (in bytes), if supported by the operating system 📏. See “Resource limits” for more information.rlimit_core— the largest size core dump file that may be created (in bytes). See “Resource limits” for more information. Defaults to0(no core dump created).rlimit_cpu— the maximum amount of CPU time that the process may use (in seconds) ⏱️. See “Resource limits” for more information.rlimit_data— the max size of the data segment for the process (in bytes, bestie). Peep“Resource limits”for the whole story. 💖rlimit_fsize— the largest size file the process is allowed to create (in bytes). Again,“Resource limits”has the deets. ✨rlimit_locks— the max number of locks the process may establish, if your OS supports it.“Resource limits”, go look. 🎀rlimit_memlock— the biggest chunk the process may lock in memory (in bytes), if the OS supports it.“Resource limits”is right there. 🦋rlimit_nofile— the max number of files the process may have open at once.“Resource limits”. That's it, that's the tweet. 🌸rlimit_nproc— the max number of processes the user may run simultaneously.“Resource limits”for more, obviously. 💅rlimit_rss— the max size the process's resident set size may grow to (in bytes).“Resource limits”. 🫶rlimit_stack— the max size the process's stack may grow to (in bytes).“Resource limits”. Same energy, different limit. 😭restricted_env_file— ok so this one sets the fully qualified path to a file stuffed with variables that get set in the environment of the program being run. Entries in this file should be assignments shaped like‘VARIABLE=value’or‘export VARIABLE=value’, separated by newline characters. The value may optionally be wrapped in single or double quotes. Shell-style variable substitution is not supported, nope, not a thing here. Empty lines and comments starting with a pound sign (‘#’) get ignored. 🔥
Variables in this file are only added if the variable doesn't already exist in the environment. And here's the plot twist: unlike env_file, the file's contents are not trusted and get processed in a manner similar to that of the invoking user's environment. So if env_reset is enabled, variables in the file will only be added if they're matched by either the env_check or env_keep list. If env_reset is disabled, variables in the file are added as long as they're not matched by the env_delete list. Either way, the contents of restricted_env_file are processed before the contents of env_file. Order matters, bestie. 👑
runchroot— if set,sudouses this value for the root directory when running a command. The special value“*”lets the user specify the root directory via sudo's-Roption. See the“Chroot_Spec”section for more. 🧚
You can only use runchroot as a command-specific Defaults setting if the command exists with the same path both inside and outside the chroot jail. This restriction does not apply to global, host, or user-based Defaults settings, or to a Cmnd_Spec that includes a Chroot_Spec. 💜
This setting is only supported by version 1.9.3 or higher. And heads up: support for setting the root directory is deprecated and will be removed in a future version of sudo. 😭
runcwd— if set,sudouses this value for the working directory when running a command. Special value“*”lets the user pick the working directory via sudo's-Doption. See the“Chdir_Spec”section. 🌈
This setting is only supported by version 1.9.3 or higher.
secure_path— if set,sudouses this value in place of the user'sPATHenvironment variable. There are two basic use cases forsecure_path, and both are lowkey iconic:- To make it possible for
sudoto find system administrator commands located in directories that may not be in the default user path, such as/usr/sbin. - To help protect scripts and programs that execute other commands without first setting
PATHto a safe value. Otherwise, a user with limited privileges may be able to run arbitrary commands by manipulating thePATHif the command being run executes other commands without using a fully-qualified path name. 💀
- To make it possible for
Users in the group specified by the exempt_group option are not affected by secure_path. This option is disabled by default. 🍓
syslog— the syslog facility if syslog is being used for logging (negate it to disable syslog logging). Defaults toauthpriv. 💅
The following syslog facilities are supported: authpriv (if your OS supports it), auth, daemon, user, local0, local1, local2, local3, local4, local5, local6, and local7. So many locals, they really said "let's make a whole neighborhood". 🏘️
syslog_badpri— the syslog priority to use when the user is not allowed to run a command, or when authentication is unsuccessful. Defaults toalert. 🚨
The following syslog priorities are supported: alert, crit, debug, emerg, err, info, notice, warning, and none. Negating the option or setting it to a value of none disables logging of unsuccessful commands. Silencing the haters, literally.
syslog_goodpri— the syslog priority to use when the user is allowed to run a command and authentication is successful. Defaults tonotice. ✨
See syslog_badpri for the list of supported syslog priorities. Negating the option or setting it to a value of none disables logging of successful commands.
verifypw— this one controls when a password will be required when a user runssudowith the-voption. It's got these possible values, and yes you need all of them:all— all the user's sudoers file entries for the current host must have theNOPASSWDflag set to avoid entering a password.always— the user must always enter a password to use the-voption.any— at least one of the user's sudoers file entries for the current host must have theNOPASSWDflag set to avoid entering a password.never— the user need never enter a password to use the-voption.
If no value is specified, a value of all is implied. Negating the option results in a value of never being used. The default value is all. 🎀
Lists that can be used in a boolean context 🦋
env_check— environment variables to be removed from the user's environment unless they're considered “safe”. For all variables exceptTZ, “safe” means the variable's value doesn't contain any‘%’or‘/’characters. This can be used to guard against printf-style format vulnerabilities in poorly-written programs. 💀
The TZ variable is considered unsafe if any of the following are true:
- It consists of a fully-qualified path name, optionally prefixed with a colon (
‘:’), that does not match the location of thezoneinfodirectory. - It contains a
..path element. - It contains white space or non-printable characters.
- It is longer than the value of
PATH_MAX.
The argument may be a double-quoted, space-separated list or a single value without double-quotes. The list can be replaced, added to, deleted from, or disabled by using the ‘=’, ‘+=’, ‘-=’, and ‘!’ operators respectively. Regardless of whether the env_reset option is enabled or disabled, variables specified by env_check will be preserved in the environment if they pass the aforementioned check. The global list of environment variables to check is displayed when sudo is run by root with the -V option. 👑
env_delete— environment variables to be removed from the user's environment when theenv_resetoption is not in effect. The argument may be a double-quoted, space-separated list or a single value without double-quotes. The list can be replaced, added to, deleted from, or disabled by using the‘=’,‘+=’,‘-=’, and‘!’operators respectively. The global list of environment variables to remove is displayed whensudois run by root with the-Voption. Many operating systems will remove potentially dangerous variables from the environment of any set-user-ID process (such assudo). 🙈env_keep— environment variables to be preserved in the user's environment when theenv_resetoption is in effect. This is the fine-grained control over the environment that sudo-spawned processes will receive, and honestly? Obsessed. The argument may be a double-quoted, space-separated list or a single value without double-quotes. The list can be replaced, added to, deleted from, or disabled by using the‘=’,‘+=’,‘-=’, and‘!’operators respectively. The global list of variables to keep is displayed whensudois run by root with the-Voption. 🌸
Preserving theHOMEenvironment variable has security implications since many programs use it when searching for configuration or data files. AddingHOMEtoenv_keepmay enable a user to run unrestricted commands viasudoand is strongly discouraged. Users wishing to edit files withsudoshould runsudoedit(orsudo -e) to get their accustomed editor configuration instead of invoking the editor directly. Like bestie, please, just usesudoedit. 😭🫶
log_servers— a list of one or more servers to use for remote event and I/O log storage, separated by white space, bestie. Heads up: those log servers must be runningsudo_logsrvdor another service that implements the protocol described bysudo_logsrv.proto(5)— no random rando servers allowed 💅
Server addresses should be of the form “host[:port][(tls)]”. The host portion may be a host name, an IPv4 address, or an IPv6 address in square brackets.
If the optional tls flag is present, the connection will be secured with Transport Layer Security (TLS) version 1.2 or 1.3. Versions of TLS prior to 1.2 are not supported (sorry to the ancient-gossip girlies, no cap 🙈).
If a port is specified, it may either be a port number or a well-known service name as defined by the system service name database. If no port is specified, port 30343 will be used for plaintext connections and port 30344 will be used for TLS connections.
When log_servers is set, event log data will be logged both locally (see the syslog and log_file settings) as well as remotely, but I/O log data will only be logged remotely. If multiple hosts are specified, they will be attempted in reverse order. If no log servers are available, the user will not be able to run a command unless either the ignore_iolog_errors flag (I/O logging enabled) or the ignore_log_errors flag (I/O logging disabled) is set. Likewise, if the connection to the log server is interrupted while sudo is running, the command will be terminated unless the ignore_iolog_errors flag (I/O logging enabled) or the ignore_log_errors flag (I/O logging disabled) is set. 😭
This setting is only supported by version 1.9.0 or higher.
passprompt_regex— a list of POSIX extended regular expressions used to match password prompts in the terminal output. As an extension, if the regular expression begins with “(?i)”, it will be matched in a case-insensitive manner. Each regular expression is limited to1024characters. This option is only used whenlog_passwordshas been disabled. The default value is “[Pp]assword[: ]*” ✨
This setting is only supported by version 1.9.10 or higher.
🌈 GROUP PROVIDER PLUGINS 🌈
Okay so this is where it gets lowkey iconic. The sudoers plugin supports its own plugin interface to allow non-Unix group lookups which can query a group source other than the standard Unix group database. This can be used to implement support for the nonunix_group syntax described earlier 🫶
Group provider plugins are specified via the group_plugin setting. The argument to group_plugin should consist of the plugin path, either fully-qualified or relative to the /usr/libexec/sudo directory, followed by any configuration options the plugin requires. These options (if specified) will be passed to the plugin's initialization function. If options are present, the string must be enclosed in double quotes ("") — the way that the quotes are non-negotiable 💀
The following group provider plugins are installed by default:
💖 group_file
The group_file plugin supports an alternate group file that uses the same syntax as the /etc/group file. The path to the group file should be specified as an option to the plugin. For example, if the group file to be used is /etc/sudo-group:
Defaults group_plugin="group_file.so /etc/sudo-group"🦋 system_group
The system_group plugin supports group lookups via the standard C library functions getgrnam(3) and getgrid(3). This plugin can be used in instances where the user belongs to groups not present in the user's supplemental group vector. This plugin takes no options:
Defaults group_plugin=system_group.soThe group provider plugin API is described in detail in sudo_plugin(5). Go read it, bestie, it's giving documentation main character energy 👑
💾 EVENT LOGGING 💾
okay so sudoers can log its little events in either JSON or sudo format, and this section is all about the sudo log format bestie. depending on how sudoers is configured, it can log events via syslog(3), to a local log file, or honestly both at once — overachiever behavior. the log format is almost identical in both cases. Any control characters hanging out in the log data get formatted in octal with a leading ‘#’ character. so for example, a horizontal tab is stored as #011 and an embedded carriage return is stored as #015 ✨. also, space characters in the command path are stored as #040. Command line arguments that contain spaces are enclosed in single quotes ('') — this is literally how you tell multiple command line arguments apart from one single argument that just happens to have spaces in it. Literal single quotes and backslash characters (\) in command line arguments are escaped with a backslash. no cap 🫶
📥 Accepted command log entries
Commands that sudo runs get logged using this exact format (split into multiple lines here just so it's readable, she's long):
date hostname progname: username : TTY=ttyname ; CHROOT=chroot ; \
PWD=cwd ; USER=runasuser ; GROUP=runasgroup ; TSID=logid ; \
ENV=env_vars COMMAND=commandWhere the fields are as follows 👇
date— The date the command was run. Typically this is in the format “MMM, DD, HH:MM:SS”. If logging viasyslog(3), the actual date format is controlled by the syslog daemon. If logging to a file and thelog_yearoption is enabled, the date will also include the year.hostname— The name of the hostsudowas run on. This field is only present when logging viasyslog(3).progname— The name of the program, usuallysudoorsudoedit. This field is only present when logging viasyslog(3).username— The login name of the user who ransudo.ttyname— The short name of the terminal (e.g., “console”, “tty01”, or “pts/0”)sudowas run on, or “unknown” if there was no terminal present.chroot— The root directory that the command was run in, if one was specified.cwd— The current working directory thatsudowas run in.runasuser— The user the command was run as.runasgroup— The group the command was run as, if one was specified on the command line.logid— An I/O log identifier that can be used to replay the command's output. This is only present when thelog_inputorlog_outputoption is enabled.env_vars— A list of environment variables specified on the command line, if specified.command— The actual command that was executed, including any command line arguments.
Messages are logged using the locale specified by sudoers_locale, which defaults to the ‘C’ locale 🎀
🚫 Denied command log entries
If the user is not allowed to run the command, the reason for the denial will follow the user name. Possible reasons include:
user NOT in sudoers— The user is not listed in the sudoers file.user NOT authorized on host— The user is listed in the sudoers file but is not allowed to run commands on the host.command not allowed— The user is listed in the sudoers file for the host but they are not allowed to run the specified command.3 incorrect password attempts— The user failed to enter their password after 3 tries. The actual number of tries will vary based on the number of failed attempts and the value of thepasswd_triesoption.a password is required— The-noption was specified but a password was required.sorry, you are not allowed to set the following environment variables— The user specified environment variables on the command line that were not allowed bysudoers.
💀 Error log entries
If an error occurs, sudoers will log a message and, in most cases, send a message to the administrator via email. Possible errors include:
parse error in /etc/sudoers near line N—sudoersencountered an error when parsing the specified file. In some cases, the actual error may be one line above or below the line number listed, depending on the type of error.problem with defaults entries— The sudoers file contains one or more unknownDefaultssettings. This does not preventsudofrom running, but the sudoers file should be checked usingvisudo.timestamp owner (username): No such user— The time stamp directory owner, as specified by thetimestampownersetting, could not be found in the password database.unable to open/read /etc/sudoers— The sudoers file could not be opened for reading. This can happen when the sudoers file is located on a remote file system that maps user-ID 0 to a different value. Normally,sudoerstries to open the sudoers file using group permissions to avoid this problem. Consider either changing the ownership of/etc/sudoersor adding an argument like “sudoers_uid=N” (where ‘N’ is the user-ID that owns the sudoers file) to the end of thesudoersPlugin line in thesudo.conf(5)file.unable to open /etc/sudoers— The/etc/sudoersfile is missing./etc/sudoers is not a regular file— The/etc/sudoersfile exists but is not a regular file or symbolic link./etc/sudoers is owned by uid N, should be 0— The sudoers file has the wrong owner. If you wish to change the sudoers file owner, add “sudoers_uid=N” (where ‘N’ is the user-ID that owns the sudoers file) to thesudoersPlugin line in thesudo.conf(5)file./etc/sudoers is world writable— The permissions on the sudoers file allow all users to write to it. The sudoers file must not be world-writable, the default file mode is0440(readable by owner and group, writable by none). The default mode may be changed via the “sudoers_mode” option to thesudoersPlugin line in thesudo.conf(5)file./etc/sudoers is owned by gid N, should be 1— The sudoers file has the wrong group ownership. If you wish to change the sudoers file group ownership, add “sudoers_gid=N” (where ‘N’ is the group-ID that owns the sudoers file) to thesudoersPlugin line in thesudo.conf(5)file.unable to open /run/sudo/ts/user-ID—sudoerswas unable to read or create the user's time stamp file. This can happen whentimestampowneris set to a user other thanrootand the mode on/run/sudois not searchable by group or other. The default mode for/run/sudois0711.unable to write to /run/sudo/ts/user-ID—sudoerswas unable to write to the user's time stamp file./run/sudo/ts is owned by uid X, should be Y— The time stamp directory is owned by a user other thantimestampowner. This can occur when the value oftimestampownerhas been changed.sudoerswill ignore the time stamp directory until the owner is corrected./run/sudo/ts is group writable— The time stamp directory is group-writable; it should be writable only bytimestampowner. The default mode for the time stamp directory is0700.sudoerswill ignore the time stamp directory until the mode is corrected.
💅 lowkey the time stamp directory stuff is the number one cause of "why is sudo asking me for my password every single time" heartbreak. check your modes bestie.
🛰️ Notes on logging via syslog
By default, sudoers logs messages via syslog(3). The date, hostname, and progname fields are added by the system's syslog(3) function, not by sudoers itself. So yeah, they may vary in format on different systems — it's giving "every system does its own thing" energy 🙈
The maximum size of syslog messages varies from system to system. The syslog_maxlen setting can be used to change the maximum syslog message size from the default value of 980 bytes. For more information, see the description of syslog_maxlen.
📝 Notes on logging to a file
If the logfile option is set, sudoers will log to a local file, such as /var/log/sudo. When logging to a file, sudoers uses a format similar to syslog(3), with a few important differences:
- The
prognamefield is not present. - The
hostnameis only logged if thelog_hostoption is enabled. - The
datedoes not include the year unless thelog_yearoption is enabled. - Lines that are longer than
loglinelencharacters (80by default) are word-wrapped and continued on the next line with a four character indent. This makes entries easier to read for a human being, but makes it more difficult to usegrep(1)on the log files. If theloglinelenoption is set to0(or negated with a ‘!’), word wrap will be disabled.
⭐ real talk: that four character indent is a gift for your eyeballs and a personal attack on your grep. pick your fighter 😭
💅 I/O LOGGING 💅
Okay bestie, this is the part where sudo becomes a whole content creator and starts recording everything 📹✨
When I/O logging is enabled, sudo will runs the command in a pseudo-terminal, logging user input and/or output, depending on which sudoers flags are enabled. There are five distinct types of I/O that can be logged, each with a corresponding sudoers flag. So cute, so organized:
- terminal input —
log_ttyin— keystrokes entered by the user ⌨️ - terminal output —
log_ttyout— command output displayed to the screen 🖥️ - standard input —
log_stdin— input from a pipe or a file 📥 - standard output —
log_stdout— output to a pipe or a file 📤 - standard error —
log_stderr— output to a pipe or a file 🚨
In addition to flags described the above, the log_input flag and LOG_INPUT command tag set both log_ttyin and log_stdin. The log_output flag and LOG_OUTPUT command tag set log_ttyout, log_stdout, and log_stderr. Like, two-for-one deals, we love a bundle 💖
To capture terminal input and output, sudo run the command in a pseudo-terminal, logging the input and output before passing it on to the user. To capture the standard input, standard output or standard error, sudo uses a pipe to interpose itself between the input or output stream, logging the I/O before passing it to the other end of the pipe. It's literally the middleman of your data and ngl it's serving main character energy 🫶
I/O can be logged either to the local machine or to a remote log server. For local logs, I/O is logged to the directory specified by the iolog_dir option (/var/log/sudo-io by default) using a unique session ID that is included in the sudo log line, prefixed with ‘TSID=’. The iolog_file option may be used to control the format of the session ID. For remote logs, the log_servers setting is used to specify one or more log servers running sudo_logsrvd or another server that implements the protocol described by sudo_logsrv.proto(5). Cloud vibes ☁️💜
🫠 I/O logging pitfals 🫠
Heads up bestie, this is the part where things get a lil goofy 😭
When logging standard input, anything sent to the standard input will be consumed, regardless of whether or not the command run via sudo is actively reading the standard input. This may have unexpected results when using sudo in a shell script that expects to process the standard input. For example, given the following shell script:
#!/bin/sh
sudo echo testing
echo doneIt will behave as expected when the script is passed to the shell as a an argument:
$ sh test.sh
testing
doneHowever, if the script is passed to the shell on the standard input, the ‘sudo echo testing’ command will consume the rest of the script. This means that the ‘echo done’ statement is never executed. Rude. Absolutely ate the whole script 💀
$ sh -s < test.sh
testingThere are several ways to work around this problem:
- Redirect the standard input from
/dev/nullwhen running a command viasudothat does not need to read the standard input.
sudo echo testing < /dev/null- Pass the script to the shell by path name instead of via the standard input.
sh test.sh- Disable logging the standard input for commands that do not need to read the standard input.
Defaults!/bin/echo !log_stdinDepending on the command, it may not be desirable to log the standard input or standard output. For example, I/O logging of commands that send or receive large amount of data via the standard output or standard input such as rsync(1) and tar(1) could fill up the log file system with superfluous data. Like, a vibe killer for your disk, fr fr 🗑️ It is possible to disable logging of the standard input and standard output for such commands as follows:
Cmnd_Alias COPY_CMDS = /usr/bin/tar, /usr/bin/cpio, /usr/bin/rsync
# Log input and output but omit stdin and stdout when copying files.
Defaults log_input, log_output
Defaults!COPY_CMDS !log_stdin, !log_stdoutHowever, be aware that using thelog_inputflag or theLOG_INPUTcommand tag will also enablelog_stdin. Likewise, thelog_ouputflag or theLOG_OUTPUTcommand tag will enablelog_stdoutandlog_stderr. Careful ordering of rules may be necessary to achieve the results that you expect. (And yes,log_ouputis spelled exactly like that in the page — i didn't do that, i would never 😭)
📁 I/O log format 📁
For both local and remote I/O logs, each log is stored in a separate directory that contains the following files. One directory per session, she's organized, she's aesthetic 🎀
log— A text file containing information about the command. The first line consists of the following colon-delimited fields: the time the command was run, the name of the user who ransudo, the name of the target user, the name of the target group (optional), the terminal thatsudowas run from, and the number of lines and columns of the terminal. The second and third lines contain the working directory the command was run from and the path name of the command itself (with arguments if present).log.json— A JSON-formatted file containing information about the command. This is similar to thelogfile but contains additional information and is easily extensible. Thelog.jsonfile will be used bysudoreplay(8)in preference to thelogfile if it exists. The file may contain the following elements:timestamp— A JSON object containing time the command was run. It consists of two values,secondsandnanoseconds.columns— The number of columns of the terminal the command ran on, or zero if no terminal was present.command— The fully-qualified path of the command that was run.lines— The number of lines of the terminal the command ran on, or zero if no terminal was present.runargv— A JSON array representing the command's argument vector as passed to theexecve(2)system call.runenv— A JSON array representing the command's environment as passed to theexecve(2)system call.rungid— The group ID the command ran as. This element is only present when the user specifies a group on the command line.rungroup— The name of the group the command ran as. This element is only present when the user specifies a group on the command line.runuid— The user ID the command ran as.runuser— The name of the user the command ran as.submitcwd— The current working directory at the timesudowas run.submithost— The name of the host the command was run on.submituser— The name of the user who ran the command viasudo.ttyname— The path name of the terminal the user invokedsudofrom. If the command was run in a pseudo-terminal,ttynamewill be different from the terminal the command actually ran in.
timing— Timing information used to replay the session. Each line consists of the I/O log entry type and amount of time since the last entry, followed by type-specific data. The I/O log entry types and their corresponding type-specific data are:0— standard input, number of bytes in the entry1— standard output, number of bytes in the entry2— standard error, number of bytes in the entry3— terminal input, number of bytes in the entry4— terminal output, number of bytes in the entry5— window change, new number lines and columns6— bug compatibility forsudo1.8.7 terminal output7— command suspend or resume, signal received
ttyin— Raw input from the user's terminal, exactly as it was received. This file is only present if thelog_inputorlog_ttyinflags are set andsudowas run from a terminal. No post-processing is performed. For manual viewing, you may wish to convert carriage return characters in the log to line feeds. For example:‘gunzip -c ttyin | tr "\r" "\n"’✨stdin— The standard input when no terminal is present, or input redirected from a pipe or file. This file is only present if thelog_inputorlog_stdinflags are set and the standard input is not connected to a terminal.ttyout— Output from the pseudo-terminal (what the command writes to the screen). Terminal-specific post-processing is performed before the data is logged. This means that, for example, line feeds are usually converted to line feed/carriage return pairs and tabs may be expanded to spaces. This file is only present if thelog_outputorlog_ttyoutflags are set andsudowas run from a terminal.stdout— The standard output when no terminal is present, or output redirected to a pipe or file. This file is only present if thelog_outputorlog_stdoutflags are set and the standard output is not connected to a terminal.stderr— The standard error when no terminal is present, or output redirected to a pipe or file. This file is only present if thelog_outputorlog_stderrflags are set and the standard error is not connected to a terminal.
All files other than log are compressed in gzip format unless the compress_io flag has been disabled. Due to buffering, it is not normally possible to display the I/O logs in real-time as the program is executing. The I/O log data will not be complete until the program run by sudo has exited or has been terminated by a signal. The iolog_flush flag can be used to disable buffering, in which case I/O log data is written to disk as soon as it is available. The output portion of an I/O log file can be viewed with the sudoreplay(8) utility, which can also be used to list or search the available logs. Replay girlies stay winning 🔥
⚠️ User input may contain sensitive information such as passwords (even if they are not echoed to the screen), which will be stored in the log file unencrypted. In most cases, logging the command output vialog_outputorLOG_OUTPUTis all that is required. When logging input, consider disabling thelog_passwordsflag. Like bestie please, protect the passwords, i am begging 🙈🔐
Since each session's I/O logs are stored in a separate directory, traditional log rotation utilities cannot be used to limit the number of I/O logs. The simplest way to limit the number of I/O is by setting the maxseq option to the maximum number of logs you wish to store. Once the I/O log sequence number reaches maxseq, it will be reset to zero and sudoers will truncate and reuse any existing I/O logs. Recycling era ♻️👑
✨ FILES ✨
Okay bestie, here's where all the actual files live, no cap:
/etc/sudo.conf— the sudo front-end configuration file 💅/etc/sudoers— the main character itself: the list of who can run what 👑/etc/group— your local groups file/etc/netgroup— the list of network groups 🦋/var/log/sudo-io— where the I/O log files hang out/run/sudo/ts— directory holding the time stamps for the sudoers security policy ⏱️/var/db/sudo/lectured— directory holding the lecture status files for the sudoers security policy 🙈/etc/environment— the initial environment for-imode on AIX and Linux systems 🌸
🎀 EXAMPLES 🎀
Here come the example sudoers file entries, and lowkey some of these are a bit contrived, ngl — the page says so itself. First up, we let a few environment variables through and then define our aliases:
# Run X applications through sudo; HOME is used to find the
# .Xauthority file. Other programs use HOME to locate configuration
# files and this may lead to privilege escalation!
Defaults env_keep += "DISPLAY HOME"
# User alias specification
User_Alias FULLTIMERS = millert, mikef, dowdy
User_Alias PARTTIMERS = bostley, jwfox, crawl
User_Alias WEBADMIN = will, wendy, wim
# Runas alias specification
Runas_Alias OP = root, operator
Runas_Alias DB = oracle, sybase
Runas_Alias ADMINGRP = adm, oper
# Host alias specification
Host_Alias SPARC = bigtime, eclipse, moet, anchor :\
SGI = grolsch, dandelion, black :\
ALPHA = widget, thalamus, foobar :\
HPPA = boa, nag, python
Host_Alias CUNETS = 128.138.0.0/255.255.0.0
Host_Alias CSNETS = 128.138.243.0, 128.138.204.0/24, 128.138.242.0
Host_Alias SERVERS = primary, mail, www, ns
Host_Alias CDROM = orion, perseus, hercules
# Cmnd alias specification
Cmnd_Alias DUMPS = /usr/bin/mt, /usr/sbin/dump, /usr/sbin/rdump,\
/usr/sbin/restore, /usr/sbin/rrestore,\
sha224:0GomF8mNN3wlDt1HD9XldjJ3SNgpFdbjO1+NsQ== \
/home/operator/bin/start_backups
Cmnd_Alias KILL = /usr/bin/kill
Cmnd_Alias PRINTING = /usr/sbin/lpc, /usr/bin/lprm
Cmnd_Alias SHUTDOWN = /usr/sbin/shutdown
Cmnd_Alias HALT = /usr/sbin/halt
Cmnd_Alias REBOOT = /usr/sbin/reboot
Cmnd_Alias SHELLS = /usr/bin/sh, /usr/bin/csh, /usr/bin/ksh,\
/usr/local/bin/tcsh, /usr/bin/rsh,\
/usr/local/bin/zsh
Cmnd_Alias SU = /usr/bin/su
Cmnd_Alias PAGERS = /usr/bin/more, /usr/bin/pg, /usr/bin/lessRight, so here we're overriding some of the compiled-in default values 💅 We want sudo to log via syslog(3) using the auth facility in all cases, and we want commands run with the target user's home directory as the working directory. We don't want to subject the full time staff to the sudo lecture (rude to make them sit through it, honestly). User millert need not provide a password, and we don't want to reset the LOGNAME or USER environment variables when running commands as root. Also! On the machines in the SERVERS Host_Alias, we keep an additional local log file and make sure we log the year in each log line, since those log entries are gonna be kept around for several years 📅 Lastly, we disable shell escapes for the commands in the PAGERS Cmnd_Alias (/usr/bin/more, /usr/bin/pg and /usr/bin/less). Heads up though — this will not effectively constrain users with sudo ALL privileges 👀
# Override built-in defaults
Defaults syslog=auth,runcwd=~
Defaults>root !set_logname
Defaults:FULLTIMERS !lecture
Defaults:millert !authenticate
Defaults@SERVERS log_year, logfile=/var/log/sudo.log
Defaults!PAGERS noexecThe User specification is the part that actually decides who may run what — it's giving main character energy for real:
root ALL = (ALL) ALL
%wheel ALL = (ALL) ALLSo we let root and any user in group wheel run any command on any host as any user 🔥
FULLTIMERS ALL = NOPASSWD: ALLFull time sysadmins (millert, mikef, and dowdy) may run any command on any host without authenticating themselves. Slay, no password needed 💖
PARTTIMERS ALL = ALLPart time sysadmins (bostley, jwfox, and crawl) may run any command on any host, but they gotta authenticate themselves first, since the entry lacks the NOPASSWD tag. Sorry babes 😭
jack CSNETS = ALLThe user jack may run any command on the machines in the CSNETS alias — that's the networks 128.138.243.0, 128.138.204.0, and 128.138.242.0. Of those networks, only 128.138.204.0 has an explicit netmask (in CIDR notation) indicating it's a class C network. For the other networks in CSNETS, the local machine's netmask gets used during matching 🦋
lisa CUNETS = ALLThe user lisa may run any command on any host in the CUNETS alias — the class B network 128.138.0.0 ✨
operator ALL = DUMPS, KILL, SHUTDOWN, HALT, REBOOT, PRINTING,\
sudoedit /etc/printcap, /usr/oper/bin/The operator user may run commands limited to simple maintenance. Here, those are the commands related to backups, killing processes, the printing system, shutting down the system, and any commands in the directory /usr/oper/bin/. One command in the DUMPS Cmnd_Alias includes a sha224 digest: /home/operator/bin/start_backups. Why? Because the directory containing that script is writable by the operator user 😬 So if the script gets modified (resulting in a digest mismatch), it will no longer be possible to run it via sudo. iykyk, integrity checks are iconic 🔐
joe ALL = /usr/bin/su operatorThe user joe may only su(1) to operator, bestie. That's it. That's the whole privilege 💀
pete HPPA = /usr/bin/passwd [A-Za-z]*, !/usr/bin/passwd *root*
%opers ALL = (: ADMINGRP) /usr/sbin/Users in the opers group may run commands in /usr/sbin/ as themselves with any group in the ADMINGRP Runas_Alias (the adm and oper groups) 🫶
Now for pete: he's allowed to change anyone's password except for root's on the HPPA machines. And here's the thing — because command line arguments are matched as a single, concatenated string, the * wildcard will match multiple words 😳 This example assumes that passwd(1) does not take multiple user names on the command line. On systems with GNU getopt(3), options to passwd(1) may be specified after the user argument. As a result, this rule will also allow:
passwd username --expire…which may not be desirable 🙈
bob SPARC = (OP) ALL : SGI = (OP) ALLThe user bob may run anything on the SPARC and SGI machines as any user listed in the OP Runas_Alias (root and operator) 👑
jim +biglab = ALLThe user jim may run any command on machines in the biglab netgroup. sudo knows that "biglab" is a netgroup because of that + prefix — cute little marker, isn't it 🌸
+secretaries ALL = PRINTING, /usr/bin/adduser, /usr/bin/rmuserUsers in the secretaries netgroup need to help manage the printers as well as add and remove users, so they're allowed to run those commands on all machines. Teamwork, periodt 💅
fred ALL = (DB) NOPASSWD: ALLThe user fred can run commands as any user in the DB Runas_Alias (oracle or sybase) without giving a password 🎉
john ALPHA = /usr/bin/su [!-]*, !/usr/bin/su *root*On the ALPHA machines, user john may su to anyone except root, but he is not allowed to specify any options to the su(1) command. Read that again, bestie — no options, none, zero 🚫
jen ALL, !SERVERS = ALLThe user jen may run any command on any machine except for those in the SERVERS Host_Alias (primary, mail, www, and ns) 😌
jill SERVERS = /usr/bin/, !SU, !SHELLSFor any machine in the SERVERS Host_Alias, jill may run any commands in the directory /usr/bin/ except for those commands belonging to the SU and SHELLS Cmnd_Aliases. And while it's not specifically mentioned in the rule, the commands in the PAGERS Cmnd_Alias all reside in /usr/bin and have the noexec option set 👀
steve CSNETS = (operator) /usr/local/op_commands/The user steve may run any command in the directory /usr/local/op_commands/, but only as user operator 💜
matt valkyrie = KILLOn his personal workstation, valkyrie, matt needs to be able to kill hung processes. Fair, honestly 😭
WEBADMIN www = (www) ALL, (root) /usr/bin/su wwwOn the host www, any user in the WEBADMIN User_Alias (will, wendy, and wim) may run any command as user www (who owns the web pages) or simply su(1) to www 🦋
ALL CDROM = NOPASSWD: /sbin/umount /CDROM,\
/sbin/mount -o nosuid\,nodev /dev/cd0a /CDROMAny user may mount or unmount a CD-ROM on the machines in the CDROM Host_Alias (orion, perseus, hercules) without entering a password. Ngl that's a bit tedious for users to type, so it's a prime candidate for encapsulating in a shell script 💡
🛡️ SECURITY NOTES 🛡️
Limitations of the ! operator 💀
Okay so real talk: it is generally not effective to "subtract" commands from ALL using the ! operator. A user can trivially circumvent this by copying the desired command to a different name and then executing that. Like, watch:
bill ALL = ALL, !SU, !SHELLSDoesn't really prevent bill from running the commands listed in SU or SHELLS, since he can simply copy those commands to a different name, or use a shell escape from an editor or other program 😬 Therefore, these kinds of restrictions should be considered advisory at best (and reinforced by policy).
And in general, if a user has sudo ALL there is nothing to prevent them from creating their own program that gives them a root shell (or making their own copy of a shell), regardless of any ! elements in the user specification. That's just the vibe check reality, sorry 🫠
Security implications of fast_glob ⚠️
If the fast_glob option is in use, it is not possible to reliably negate commands where the path name includes globbing (aka wildcard) characters. Why? Because the C library's fnmatch(3) function cannot resolve relative paths. While this is typically only an inconvenience for rules that grant privileges, it can result in a security issue for rules that subtract or revoke privileges. That's the part you gotta pay attention to 👀
For example, given the following sudoers file entry:
john ALL = /usr/bin/passwd [a-zA-Z0-9]*, /usr/bin/chsh [a-zA-Z0-9]*,\
/usr/bin/chfn [a-zA-Z0-9]*, !/usr/bin/* rootUser john can still run /usr/bin/passwd root if fast_glob is enabled — by changing to /usr/bin and running ./passwd root instead. Boom, restriction dodged 💀
Another potential issue is that when sudo executes the command, it must use the command or path specified by the user instead of a path listed in the sudoers file. This may lead to a time of check versus time of use race condition 😱
Wildcards in command arguments 🌈
Command line arguments are matched as a single, concatenated string. This means a wildcard character such as ? or * will match across word boundaries, which may be unexpected. For example, while a sudoers entry like:
so like, <pink>lowkey</pink> this wildcard thing has a whole vibe check problem, bestie:
%operator ALL = /bin/cat /var/log/messages*that line will allow a command like:
$ sudo cat /var/log/messages.1...which is fine, cute, slay. but it will also allow:
$ sudo cat /var/log/messages /etc/shadowwhich is <hotpink>probably not what was intended</hotpink> 😭💀. a safer alternative is to use a regular expression for matching command line arguments. the above example can be rewritten as a regex, like:
%operator ALL = /bin/cat ^/var/log/messages[^[:space:]]*$the regex will only match a single file with a name that begins with /var/log/messages and does not include any white space in the name. ngl, it is often better to do command line processing outside of the sudoers file in a scripting language for anything non-trivial 🫶.
Regular expressions in command names
okay so using a regex to match a command name has the same security implications as using the fast_glob option, fr fr:
- It is not possible to reliably negate commands when the path name is a regular expression. 🙈
- When
sudoexecutes the command, it must use the command or path specified by the user instead of a path listed in the sudoers file. this may lead to a time of check versus time of use race condition 😬.
the good news? these issues do not apply to rules where only the command line options are matched using a regular expression ✨.
Preventing shell escapes
once sudo executes a program, that program is free to do whatever it pleases — including run other programs 👀. this can be a security issue since it is not uncommon for a program to allow shell escapes, which lets a user bypass sudo's access control and logging. common programs that permit shell escapes include shells (obviously), editors, paginators, mail, and terminal programs 🎀.
there are four basic approaches to this problem:
- restrict — avoid giving users access to commands that allow the user to run arbitrary commands. many editors have a restricted mode where shell escapes are disabled, though
sudoeditis a better solution to running editors viasudo. due to the large number of programs that offer shell escapes, restricting users to the set of programs that do not is often unworkable 💀. - intercept — on most systems,
sudo's intercept functionality can be used to transparently intercept an attempt to run a new command, allow or deny it based on sudoers rules, and log the result. for example, this can be used to restrict the commands run from within a privileged shell or editor. however, not all programs operate correctly when intercept is enabled 😭.
there are two underlying mechanisms that may be used to implement intercept mode: dso and trace. the intercept_type setting can be used to select between them.
the first mechanism, dso, overrides the standard C library functions that are used to execute a command. it does this by setting an environment variable (usually LD_PRELOAD) to the path of a dynamic shared object, or shared library, containing custom versions of the execve(2), execl(3), execle(3), execlp(3), execv(3), execvp(3), execvpe(3), and system(3) library functions that connect back to sudo for a policy decision. note, however, that this applies only to dynamically-linked executables 👑. it is not possible to intercept commands for statically-linked executables or executables that run under binary emulation this way. because most dynamic loaders ignore LD_PRELOAD (or the equivalent) when running set-user-ID and set-group-ID programs, sudoers will not permit such programs to be run in intercept mode by default. the dso mechanism is incompatible with sudo's SELinux RBAC support (but see below). SELinux disables LD_PRELOAD by default and interferes with file descriptor inheritance, which sudo relies on 😤.
the second mechanism, trace, is available on Linux systems that support seccomp(2) filtering. it uses ptrace(2) and seccomp(2) to intercept the execve(2) system call instead of pre-loading a dynamic shared object. both static and dynamic executables are supported and it is compatible with sudo's SELinux RBAC mode 🌈. functions utilizing the execveat(2) system call, such as fexecve(3), are not currently intercepted. programs that rely on ptrace(2) themselves, such as debuggers and system call tracers (such as strace(1) and truss(1)) will be unable to function if intercept is enabled in trace mode. this same restriction applies to the log_subcmds sudoers option 🫠.
the intercept feature is known to work on Solaris, *BSD, Linux, macOS, HP-UX 11.x and AIX 5.3 and above. it should be supported on most operating systems that support the LD_PRELOAD environment variable or an equivalent. it is not possible to intercept shell built-in commands or restrict the ability to read or write sensitive files from within a shell 💅.
to enable intercept mode on a per-command basis, use the INTERCEPT tag as documented in the User Specification section above. here is that example again:
chuck research = INTERCEPT: ALLthis allows user chuck to run any command on the machine “research” in intercept mode. any commands run via shell escapes will be validated and logged by sudo ⭐. if you are unsure whether or not your system is capable of supporting intercept, you can always just try it out and check whether or not external commands run via a shell are logged when intercept is enabled 😌.
there is an inherent race condition between when a command is checked against sudoers rules and when it is actually executed. if a user is allowed to run arbitrary commands, they may be able to change theexecve(2)arguments in the program after the sudoers policy check has completed but before the new command is executed 😱. starting with version1.9.12, thetracemethod will verify that the command and its arguments have not changed afterexecve(2)has completed but before execution of the new program has had a chance to run. this is not the case with thedsomethod. see the description of theintercept_verifysetting for more information.
- log — there are two separate but related ways to log additional commands. the first is to enable I/O logging using the
log_outputflag. this will log the command's output but will not create an event log entry when the additional command is run. the second is to enable thelog_subcmdsflag in sudoers which will create an event log entry every time a new command is run 📝. if I/O logging is also enabled, the log entry will include a time offset into the I/O log to indicate when the command was run. this offset can be passed to thesudoreplay(8)utility to replay the I/O log at the exact moment when the command was run 🔥. thelog_subcmdsflag uses the same mechanism as intercept (see above) and has the same limitations. - noexec —
sudo's noexec functionality can be used to prevent a program run bysudofrom executing any other programs 🚫. on most systems, it uses the sameLD_PRELOADmechanism as intercept (see above) and thus the same caveats apply. the noexec functionality is capable of blocking execution of commands run via theexecve(2),execl(3),execle(3),execlp(3),exect(3),execv(3),execveat(3),execvP(3),execvp(3),execvpe(3),fexecve(3),popen(3),posix_spawn(3),posix_spawnp(3),system(3), andwordexp(3)functions. on Linux, aseccomp(2)filter is used to implement noexec. on Solaris 10 and higher, noexec uses Solaris privileges instead of theLD_PRELOADenvironment variable ✨.
to enable noexec for a command, use the NOEXEC tag as documented in the User Specification section above. here is that example again:
aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vithis allows user aaron to run /usr/bin/more and /usr/bin/vi with noexec enabled. this will prevent those two commands from executing other commands (such as a shell) 🐚. if you are unsure whether or not your system is capable of supporting noexec you can always just try it out and check whether shell escapes work when noexec is enabled 😇.
restricting shell escapes is not a panacea, bestie. programs running as root are still capable of many potentially hazardous operations (such as changing or overwriting files) that could lead to unintended privilege escalation 😳. in the specific case of an editor, a safer approach is to give the user permission to run sudoedit (see below) 💖.
Secure editing
the sudoers plugin includes sudoedit support which allows users to securely edit files with the editor of their choice 🎀. as sudoedit is a built-in command, it must be specified in the sudoers file without a leading path. however, it may take command line arguments just as a normal command does. wildcards used in sudoedit command line arguments are expected to be path names, so a forward slash (‘/’) will not be matched by a wildcard 🌸.
unlike other sudo commands, the editor is run with the permissions of the invoking user and with the environment unmodified. more information may be found in the description of the -e option in sudo(8) 📖.
for example, to allow user operator to edit the “message of the day” file on any machine:
operator ALL = sudoedit /etc/motdthe operator user then runs sudoedit as follows:
$ sudoedit /etc/motdthe editor will run as the operator user, not root, on a temporary copy of /etc/motd. after the file has been edited, /etc/motd will be updated with the contents of the temporary copy ✅💜.
Okay bestie, we're picking right back up mid-security-notes, so buckle up 💅
Users should never be granted sudoedit permission to edit a file that lives in a directory the user has write access to, whether that's directly or via a wildcard. Why? Because if the user can write to the directory, they can straight-up swap the legit file for a link to some other file, and then they're editing arbitrary files. Not the vibe. 🚩
To stop that: starting in version 1.8.16, symbolic links will not be followed in writable directories, and sudoedit will refuse to edit a file that sits in a writable directory — unless the sudoedit_checkdir option has been disabled, or the invoking user is root. Also, in version 1.8.15 and higher, sudoedit will refuse to open a symbolic link unless either the sudoedit_follow option is enabled or the sudoedit command is prefixed with the FOLLOW tag in the sudoers file. No cap. 🦋
⏰ Time stamp file checks 🎀
sudoers will check the ownership of its time stamp directory (/run/sudo/ts by default) and will ignore whatever's in that directory if it isn't owned by root, or if it's writable by any user who isn't root. Old versions of sudo stored time stamp files in /tmp — that is no longer recommended, because it may be possible for a user to create the time stamp themselves on systems that let unprivileged users change the ownership of files they create. 😬
Ideally the time stamp directory gets cleared at reboot time, but not every system has a /run or /var/run directory. So to dodge potential problems, sudoers will ignore time stamp files that date from before the machine booted — on systems where the boot time is actually available. 🕰️
Some systems with graphical desktop environments let unprivileged users change the system clock. Since sudoers relies on the system clock for time stamp validation, on those systems it may be possible for a user to run sudo for longer than timestamp_timeout just by setting the clock back 🙈. To fight that, sudoers uses a monotonic clock (which never moves backwards) for its time stamps, if the system supports it. Slay.
sudoers will not honor time stamps set far in the future. Time stamps with a date greater than current_time + 2 * TIMEOUT get ignored, and sudoers will log and complain about it. 💀
If the timestamp_type option is set to “tty”, the time stamp record includes the device number of the terminal the user authenticated with. That gives you per-terminal granularity, but the time stamp records may still outlive the user's session. 🖥️
Unless the timestamp_type option is set to “global”, the time stamp record also includes the session ID of the process that last authenticated. That stops processes in different terminal sessions from sharing the same time stamp record. On systems where a process's start time can be queried, the start time of the session leader gets recorded in the time stamp record. If there's no terminal present, or the timestamp_type option is set to “ppid”, then the start time of the parent process is used instead. In most cases this prevents a time stamp record from being reused without the user entering a password when they log out and back in again. 🔐
🐛 DEBUGGING 🐛
Versions 1.8.4 and higher of the sudoers plugin support a flexible debugging framework that can help track down what the plugin is doing internally if something's acting up. You configure it in the sudo.conf(5) file. 🎀
The sudoers plugin uses the same debug flag format as the sudo front-end, and that format is:
subsystem@priorityThe priorities used by sudoers, in order of decreasing severity, are: crit, err, warn, notice, diag, info, trace, and debug. Each priority, when you specify it, also includes all the priorities higher than it. So for example, a priority of notice would include debug messages logged at notice and higher. Ik how that works. ✨
The following subsystems are used by the sudoers plugin 👇
alias—User_Alias,Runas_Alias,Host_AliasandCmnd_Aliasprocessingall— matches every subsystemaudit— BSM and Linux audit codeauth— user authenticationdefaults— sudoers fileDefaultssettingsenv— environment handlingldap— LDAP-based sudoerslogging— logging supportmatch— matching of users, groups, hosts, and netgroups in the sudoers filenetif— network interface handlingnss— network service switch handling in sudoersparser— sudoers file parsingperms— permission settingplugin— the equivalent ofmainfor the pluginpty— pseudo-terminal related coderbtree— redblack tree internalssssd— SSSD-based sudoersutil— utility functions
For example:
Debug sudoers.so /var/log/sudoers_debug match@info,nss@infoFor more info, see the sudo.conf(5) manual. 🫶
👀 SEE ALSO 👀
ssh(1), su(1), fnmatch(3), glob(3), mktemp(3), strftime(3), sudo.conf(5), sudo_logsrv.proto(5), sudo_plugin(5), sudoers.ldap(5), sudoers_timestamp(5), sudo(8), sudo_logsrvd(8), visudo(8)
👑 AUTHORS 👑
So many people have worked on sudo over the years — the version you're reading consists of code written primarily by:
Todd C. MillerSee the CONTRIBUTORS.md file in the sudo distribution (https://www.sudo.ws/about/contributors/) for an exhaustive list of everyone who's contributed to sudo. Legends, all of them. 💖
⚠️ CAVEATS ⚠️
The sudoers file should always be edited by the visudo utility, because that's the thing that locks the file and checks for syntax errors. If sudoers contains syntax errors, sudo may refuse to run — which is a serious problem if sudo is your only way of getting superuser privileges. 😭
Recent versions of sudoers will attempt to recover after a syntax error by ignoring the rest of the line after encountering an error. Older versions of sudo will flat-out not run if sudoers contains a syntax error. 💀
When you're using netgroups of machines (as opposed to users), and you store a fully qualified host name in the netgroup (which is usually the case), you either need to have the machine's host name be fully qualified as returned by the hostname command, or use the fqdn option in sudoers. 🖥️
💀 BUGS 💀
If you think you've found a bug in sudoers, you can either file a bug report in the sudo bug database, https://bugzilla.sudo.ws/, or open an issue at https://github.com/sudo-project/sudo/issues. If you'd rather use email, messages may be sent to the sudo-workers mailing list, https://www.sudo.ws/mailman/listinfo/sudo-workers (public) or <sudo@sudo.ws> (private). 🐛
Please do not report security vulnerabilities through public GitHub issues, Bugzilla or mailing lists. Instead, report them via email to<Todd.Miller@sudo.ws>. You're welcome to encrypt your message with PGP if you'd like, using the key found athttps://www.sudo.ws/dist/PGPKEYS. 🔐
🫶 SUPPORT 🫶
Limited free support is available via the sudo-users mailing list — see https://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or search the archives. 🍓
📜 DISCLAIMER 📜
sudo is provided “AS IS” and any express or implied warranties, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose are disclaimed. See the LICENSE.md file distributed with sudo or https://www.sudo.ws/about/license/ for complete details. 💅
And that's the whole page, bestie — you made it to the end! 🎉 This gem is from Sudo 1.9.17p2, dated June 7, 2025, and it's SUDOERS(5) — go forth and visudo responsibly, mwah 💖✨🎀
📦 where this page comes from
- centos-stream 9: sudo 1.9.17p2-6.el9 · ISC
- 📜 the page's license: ISC
- Copyright (c) 1994-1996, 1998-2005, 2007-2025 Todd C. Miller <Todd.Miller@sudo.ws>
- 💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash-1017 on : a language model's rewrite of the original, under its terms