Config...s::Ssh(3pm)

📦
version 2.10.2.1 · 5 versions
, in ubuntu resolute, ubuntu stonking

🌸 NAME 🌸

Config::Model::models::Ssh — Configuration class Ssh

(yes bestie, this is that Config...s::Ssh(3pm) page from the User Contributed Perl Documentation, we're doing this 💅)

✨ DESCRIPTION ✨

okay so the whole point: these are the configuration classes used by Config::Model 💖

This configuration class was generated from ssh_system documentation by parse-man.pl (https://github.com/dod38fr/config-model-openssh/contrib/parse-man.pl) — so a script wrote it, not me, I'm just here to make it make sense 🫶

🌈 Elements 🌈

🏠 Host

Restricts the following declarations (up to the next Host or Match keyword) to be only for those hosts that match one of the patterns given after the keyword. If more than one pattern is provided, they should be separated by whitespace. A single '*' as a pattern can be used to provide global defaults for all hosts. The host is usually the hostname argument given on the command line (see the CanonicalizeHostname keyword for exceptions) ✨

A pattern entry may be negated by prefixing it with an exclamation mark ('!'). If a negated entry is matched, then the Host entry is ignored, regardless of whether any other patterns on the line match. Negated matches are therefore useful to provide exceptions for wildcard matches 🎀

See PATTERNS for more information on patterns.

Optional. Type: hash of node of class Ssh::HostElement.

🔑 AddKeysToAgent

Specifies whether keys should be automatically added to a running ssh-agent1. If this option is set to yes and a key is loaded from a file, the key and its passphrase are added to the agent with the default lifetime, as if by ssh-add1. If this option is set to ask, ssh(1) will require confirmation using the SSH_ASKPASS program before adding a key (see ssh-add1 for details). If this option is set to confirm, each use of the key must be confirmed, as if the -c option was specified to ssh-add1. If this option is set to no, no keys are added to the agent 🙈

Alternately, this option may be specified as a time interval using the format described in the TIME FORMATS section of sshd_config5 to specify the key's lifetime in ssh-agent1, after which it will automatically be removed.

The argument must be no (the default), yes, confirm (optionally followed by a time interval), ask or a time interval.

Optional. Type: enum. Choice: 'ask', 'confirm', 'no', 'yes'.

upstream_default value: no

🌐 AddressFamily

Specifies which address family to use when connecting. Valid arguments are any (the default), inet (use IPv4 only), or inet6 (use IPv6 only).

Optional. Type: enum. Choice: 'any', 'inet', 'inet6'.

upstream_default value: any

🤖 BatchMode

If set to yes, user interaction such as password prompts and host key confirmation requests will be disabled. In addition, the ServerAliveInterval option will be set to 300 seconds by default (Debian-specific). This option is useful in scripts and other batch jobs where no user is present to interact with ssh(1), and where it is desirable to detect a broken network swiftly 🫡

The argument must be yes or no (the default).

Optional. Type: boolean.

upstream_default value: no

📍 BindAddress

Use the specified address on the local machine as the source address of the connection. Only useful on systems with more than one address.

Optional. Type: uniline.

🎀 BindInterface

Use the address of the specified interface on the local machine as the source address of the connection.

Optional. Type: uniline.

🗂️ CanonicalDomains

When CanonicalizeHostname is enabled, this option specifies the list of domain suffixes in which to search for the specified destination host.

Optional. Type: uniline.

🩹 CanonicalizeFallbackLocal

Specifies whether to fail with an error when hostname canonicalization fails. The default, yes, will attempt to look up the unqualified hostname using the system resolver's search rules. A value of no will cause ssh(1) to fail instantly if CanonicalizeHostname is enabled and the target hostname cannot be found in any of the domains specified by CanonicalDomains.

Optional. Type: boolean.

upstream_default value: yes

🪄 CanonicalizeHostname

Controls whether explicit hostname canonicalization is performed. The default, no, is not to perform any name rewriting and let the system resolver handle all hostname lookups. If set to yes then, for connections that do not use a ProxyCommand or ProxyJump, ssh(1) will attempt to canonicalize the hostname specified on the command line using the CanonicalDomains suffixes and CanonicalizePermittedCNAMEs rules. If CanonicalizeHostname is set to always then canonicalization is applied to proxied connections too 🔥

If this option is enabled, then the configuration files are processed again using the new target name to pick up any new configuration in matching Host and Match stanzas. A value of none disables the use of a ProxyJump host.

Optional. Type: enum. Choice: 'always', 'no', 'none', 'yes'.

upstream_default value: no

🔢 CanonicalizeMaxDots

Specifies the maximum number of dot characters in a hostname before canonicalization is disabled. The default, 1, allows a single dot (i.e. hostname.subdomain).

Optional. Type: integer.

upstream_default value: 1

🧬 CanonicalizePermittedCNAMEs

Specifies rules to determine whether CNAMEs should be followed when canonicalizing hostnames. The rules consist of one or more arguments of source_domain_list:target_domain_list where source_domain_list is a pattern-list of domains that may follow CNAMEs in canonicalization, and target_domain_list is a pattern-list of domains that they may resolve to 🦋

For example, *.a.example.com:*.b.example.com,*.c.example.com will allow hostnames matching *.a.example.com to be canonicalized to names in the *.b.example.com or *.c.example.com domains.

A single argument of none causes no CNAMEs to be considered for canonicalization. This is the default behaviour.

Optional. Type: uniline.

✍️ CASignatureAlgorithms

Specifies which algorithms are allowed for signing of certificates by certificate authorities (CAs). The default is:

ssh-ed25519, ecdsa-sha2-nistp256, ecdsa-sha2-nistp384, ecdsa-sha2-nistp521, sk-ssh-ed25519@openssh.com, sk-ecdsa-sha2-nistp256@openssh.com, rsa-sha2-512, rsa-sha2-256

If the specified list begins with a '+' character, then the specified algorithms will be appended to the default set instead of replacing them. If the specified list begins with a '-' character, then the specified algorithms (including wildcards) will be removed from the default set instead of replacing them 💅

ssh(1) will not accept host certificates signed using algorithms other than those specified.

Optional. Type: uniline.

📜 CertificateFile

Specifies a file from which the user's certificate is read. A corresponding private key must be provided separately in order to use this certificate, either from an IdentityFile directive or -i flag to ssh(1), via ssh-agent1, or via a PKCS11Provider or SecurityKeyProvider.

Arguments to CertificateFile may use the tilde syntax to refer to a user's home directory, the tokens described in the TOKENS section and environment variables as described in the ENVIRONMENT VARIABLES section 🎀

It is possible to have multiple certificate files specified in configuration files; these certificates will be tried in sequence. Multiple CertificateFile directives will add to the list of certificates used for authentication.

Optional. Type: uniline.

⏳ ChannelTimeout

Specifies whether and how quickly ssh(1) should close inactive channels. Timeouts are specified as one or more type=interval pairs separated by whitespace, where the type must be the special keyword global or a channel type name from the list below, optionally containing wildcard characters 🌈

The timeout value interval is specified in seconds or may use any of the units documented in the TIME FORMATS section. For example, session=5m would cause interactive sessions to terminate after five minutes of inactivity. Specifying a zero value disables the inactivity timeout.

The special timeout global applies to all active channels, taken together. Traffic on any active channel will reset the timeout, but when the timeout expires then all open channels will be closed. Note that this global timeout is not matched by wildcards and must be specified explicitly 👑

The available channel type names include:

  • agent-connection — Open connections to ssh-agent1.
  • direct-tcpip, direct-streamlocal@openssh.com — Open TCP or Unix socket (respectively) connections that have been established from an ssh(1) local forwarding, i.e. LocalForward or DynamicForward.
  • forwarded-tcpip, forwarded-streamlocal@openssh.com — Open TCP or Unix socket (respectively) connections that have been established to an sshd(8) listening on behalf of an ssh(1) remote forwarding, i.e. RemoteForward.
  • session — The interactive main session, including shell session, command execution, scp(1), sftp(1), etc.
  • tun-connection — Open TunnelForward connections.
  • x11-connection — Open X11 forwarding sessions.

Note that in all the above cases, terminating an inactive session does not guarantee to remove all resources associated with the session, e.g. shell processes or X11 clients relating to the session may continue to execute 😭

Moreover, terminating an inactive channel or session does not necessarily close the SSH connection, nor does it prevent a client from requesting another channel of the same type. In particular, expiring an inactive forwarding session does not prevent another identical forwarding from being subsequently created 🙈

The default is not to expire channels of any type for inactivity.

Optional. Type: uniline.

🕵️ CheckHostIP

If set to yes, ssh(1) will additionally check the host IP address in the known_hosts file. This allows it to detect if a host key changed due to DNS spoofing and will add addresses of destination hosts to ~/.ssh/known_hosts in the process, regardless of the setting of StrictHostKeyChecking. If the option is set to no (the default), the check will not be executed.

Optional. Type: boolean.

upstream_default value: no

🔐 Ciphers

Specifies the ciphers allowed and their order of preference. Multiple ciphers must be comma-separated. If the specified list begins with a '+' character, then the specified ciphers will be appended to the default set instead of replacing them. If the specified list begins with a '-' character, then the specified ciphers (including wildcards) will be removed from the default set instead of replacing them. If the specified list begins with a '^' character, then the specified ciphers will be placed at the head of the default set ⭐

The supported ciphers are:

3des-cbc aes128-cbc aes192-cbc aes256-cbc aes128-ctr aes192-ctr aes256-ctr aes128-gcm@openssh.comaes256-gcm@openssh.comchacha20-poly1305@openssh.com

🍓 and that's where part 1 wraps, bestie — more is coming...

The default is: chacha20-poly1305@openssh.com, aes128-gcm@openssh.com, aes256-gcm@openssh.com, aes128-ctr, aes192-ctr, aes256-ctr

You can also just ask for the list of available ciphers, bestie, it's literally one command: ssh -Q cipher 💅 Optional. Type uniline.

ClearAllForwardings

Okay so this one nukes all your local, remote, and dynamic port forwardings — the ones set in config files and the ones on the command line. It's mainly a ssh(1) command-line move, for clearing out port forwardings that snuck in via config files, and scp(1) and sftp(1) set it automatically. The argument must be yes or no (the default). Optional. Type boolean.

upstream_default value :
    no

Compression

Do we compress or not. The argument must be yes or no (the default). Optional. Type boolean. 🫶

upstream_default value :
    no

ConnectionAttempts

How many tries (one per second) before it gives up and exits. Argument must be an integer. Lowkey useful in scripts when your connection is being flaky 😭. The default is 1. Optional. Type integer.

upstream_default value :
    1

ConnectTimeout

Timeout (in seconds) used when connecting to the SSH server, instead of the default system TCP timeout. And bestie, it applies to both establishing the connection and doing the initial SSH protocol handshake and key exchange — the whole glow-up, not just the first step ✨. SetupTimeOut is a Debian-specific compatibility alias for this option. Optional. Type integer.

ControlMaster

Multiplexing!! This is the main character of connection sharing 👑. It enables sharing multiple sessions over a single network connection. When set to yes, ssh(1) listens for connections on a control socket specified by the ControlPath argument. Additional sessions can connect to that socket using the same ControlPath with ControlMaster set to no (the default). Those sessions try to reuse the master instance's network connection instead of starting new ones, but they'll fall back to connecting normally if the control socket doesn't exist or isn't listening. No stress, it just works.

Setting it to ask makes ssh(1) listen for control connections but require confirmation via ssh-askpass(1). If the ControlPath can't be opened, ssh(1) will just continue without connecting to a master instance. We move 🦋.

X11 and ssh-agent(1) forwarding are supported over these multiplexed connections — however, the display and agent forwarded will be the one belonging to the master connection, i.e. it is not possible to forward multiple displays or agents. One display, one agent, that's the vibe. Periodt.

Two extra options allow for opportunistic multiplexing: try to use a master connection but fall back to creating a new one if one doesn't already exist. Those options are auto and autoask. The latter requires confirmation like the ask option. Optional. Type enum. choice: 'ask', 'auto', 'autoask', 'no', 'yes'.

upstream_default value :
    no

ControlPath

Specify the path to the control socket used for connection sharing, as described in the ControlMaster section above, or the string none to disable connection sharing. Arguments to ControlPath may use the tilde syntax to refer to a user's home directory, the tokens described in the TOKENS section, and environment variables as described in the ENVIRONMENT VARIABLES section.

Important rec, bestie: it is recommended that any ControlPath used for opportunistic connection sharing include at least %h, %p, and %r (or alternatively %C) and be placed in a directory that is not writable by other users. This ensures that shared connections are uniquely identified. Optional. Type uniline. 🎀

ControlPersist

Used in conjunction with ControlMaster, this specifies that the master connection should remain open in the background (waiting for future client connections) after the initial client connection has been closed.

  • If set to no (the default), then the master connection will not be placed into the background, and will close as soon as the initial client connection is closed.
  • If set to yes or 0, then the master connection will remain in the background indefinitely (until killed or closed via a mechanism such as ssh -O exit).
  • If set to a time in seconds, or a time in any of the formats documented in sshd_config(5), then the backgrounded master connection will automatically terminate after it has remained idle (with no client connections) for the specified time.

Optional. Type uniline. 💅

DynamicForward

Specifies that a TCP port on the local machine be forwarded over the secure channel, and the application protocol is then used to determine where to connect to from the remote machine. It's giving proxy energy ✨.

The argument must be [bind_address:]port. IPv6 addresses can be specified by enclosing addresses in square brackets. By default, the local port is bound in accordance with the GatewayPorts setting. However, an explicit bind_address may be used to bind the connection to a specific address. The bind_address of localhost indicates that the listening port be bound for local use only, while an empty address or '*' indicates that the port should be available from all interfaces.

Currently the SOCKS4 and SOCKS5 protocols are supported, and ssh(1) will act as a SOCKS server. Multiple forwardings may be specified, and additional forwardings can be given on the command line. Only the superuser can forward privileged ports. Optional. Type list of uniline. 🌈

EnableEscapeCommandline

Enables the command line option in the EscapeChar menu for interactive sessions (default '~C'). By default, the command line is disabled. Optional. Type uniline.

EnableSSHKeysign

Setting this option to yes in the global client configuration file /etc/ssh/ssh_config enables the use of the helper program ssh-keysign(8) during HostbasedAuthentication. The argument must be yes or no (the default). This option should be placed in the non-hostspecific section. See ssh-keysign(8) for more information. Optional. Type boolean. 🧚

upstream_default value :
    no

EscapeChar

Sets the escape character (default: '~'). The escape character can also be set on the command line. The argument should be a single character, '^' followed by a letter, or none to disable the escape character entirely (making the connection transparent for binary data — very binary-safe of it 💅). Optional. Type uniline.

ExitOnForwardFailure

Specifies whether ssh(1) should terminate the connection if it cannot set up all requested dynamic, tunnel, local, and remote port forwardings, (e.g. if either end is unable to bind and listen on a specified port).

Heads up bestie: ExitOnForwardFailure does not apply to connections made over port forwardings and will not, for example, cause ssh(1) to exit if TCP connections to the ultimate forwarding destination fail. Different thing entirely, ok?? 😤

The argument must be yes or no (the default). Optional. Type boolean.

upstream_default value :
    no

FingerprintHash

Specifies the hash algorithm used when displaying key fingerprints. Valid options are: md5 and sha256 (the default). Optional. Type enum. choice: 'md5', 'sha256'.

upstream_default value :
    sha256

ForkAfterAuthentication

Requests ssh to go to background just before command execution. This is useful if ssh is going to ask for passwords or passphrases, but the user wants it in the background. This implies the StdinNull configuration option being set to ''yes''. The recommended way to start X11 programs at a remote site is with something like ssh -f host xterm, which is the same as ssh host xterm if the ForkAfterAuthentication configuration option is set to ''yes''.

If the ExitOnForwardFailure configuration option is set to ''yes'' then a client started with the ForkAfterAuthentication configuration option being set to ''yes'' will wait for all remote port forwards to be successfully established before placing itself in the background. The argument to this keyword must be yes (same as the -f option) or no (the default). Optional. Type boolean.

upstream_default value :
    no

ForwardAgent

Specifies whether the connection to the authentication agent (if any) will be forwarded to the remote machine. The argument may be yes, no (the default), an explicit path to an agent socket, or the name of an environment variable (beginning with '$') in which to find the path.

⚠️ Agent forwarding should be enabled with caution. Users with the ability to bypass file permissions on the remote host (for the agent's Unix-domain socket) can access the local agent through the forwarded connection. An attacker cannot obtain key material from the agent — however they can perform operations on the keys that enable them to authenticate using the identities loaded into the agent. So like, be smart about it, bestie. 😭

Optional. Type boolean.

upstream_default value :
    no

ForwardX11

Specifies whether X11 connections will be automatically redirected over the secure channel and DISPLAY set. The argument must be yes or no (the default).

⚠️ X11 forwarding should be enabled with caution. Users with the ability to bypass file permissions on the remote host (for the user's X11 authorization database) can access the local X11 display through the forwarded connection. An attacker may then be able to perform activities such as keystroke monitoring if the ForwardX11Trusted option is also enabled. 💀

Optional. Type boolean.

upstream_default value :
    no

ForwardX11Timeout

Specify a timeout for untrusted X11 forwarding using the format described in the TIME FORMATS section of sshd_config(5). X11 connections received by ssh(1) after this time will be refused. Setting ForwardX11Timeout to zero will disable the timeout and permit X11 forwarding for the life of the connection. The default is to disable untrusted X11 forwarding after twenty minutes has elapsed. Optional. Type integer. ⏰

ForwardX11Trusted

  • If this option is set to yes (the Debian-specific default), remote X11 clients will have full access to the original X11 display.
  • If this option is set to no (the upstream default), remote X11 clients will be considered untrusted and prevented from stealing or tampering with data belonging to trusted X11 clients. Furthermore, the xauth(1) token used for the session will be set to expire after 20 minutes. Remote clients will be refused access after this time.

See the X11 SECURITY extension specification for full details on the restrictions imposed on untrusted clients. Optional. Type boolean. 🔥

GatewayPorts

Specifies whether remote hosts are allowed to connect to local forwarded ports. By default, ssh(1) binds local port forwardings to the loopback address. This prevents other remote hosts from connecting to forwarded ports. GatewayPorts can be used to specify that ssh should bind local port forwardings to the wildcard address, thus allowing remote hosts to connect to forwarded ports. The argument must be yes or no (the default). Optional. Type boolean. 🌸

upstream_default value :
    no

🌸 GlobalKnownHostsFile

Tells ssh which file(s) to use as the global host key database, bestie — and if you've got more than one, just separate them with whitespace. Default is /etc/ssh/ssh_known_hosts /etc/ssh/ssh_known_hosts2. Optional, and it's type uniline.

default value :
    /etc/ssh/ssh_known_hosts /etc/ssh/ssh_known_hosts2

🎀 GSSAPIAuthentication

Says whether user auth based on GSSAPI is allowed or not. Default? no. Optional, type boolean.

upstream_default value :
    no

🦋 GSSAPIClientIdentity

If you set this, it specifies the GSSAPI client identity ssh should use when it connects to the server. Default is unset, which lowkey just means "use the default identity, bestie." Optional, type uniline.

💅 GSSAPIDelegateCredentials

Forwards (aka delegates) your credentials to the server. Default is no. Optional, type boolean.

upstream_default value :
    no

✨ GSSAPIKeyExchange

Specifies whether key exchange based on GSSAPI may be used. The tea here: when you're using GSSAPI key exchange, the server doesn't even need to have a host key. The default is ''no''. Optional, type uniline.

👑 GSSAPIRenewalForcesRekey

Set it to ''yes'' and renewal of the client's GSSAPI credentials will force the rekeying of the ssh connection. And with a compatible server, this will delegate the renewed credentials to a session on the server. Iconic behaviour tbh.

Checks are made to ensure that credentials are only propagated when the new credentials match the old ones on the originating client, and where the receiving server still has the old set in its cache.

The default is ''no''.

For this to work, GSSAPIKeyExchange needs to be enabled in the server and also used by the client.

Optional, type uniline.

🧚 GSSAPIServerIdentity

If set, specifies the GSSAPI server identity that ssh should expect when connecting to the server. Default is unset, which means the expected GSSAPI server identity will be figured out from the target hostname. Optional, type uniline.

🌈 GSSAPITrustDns

Set it to ''yes'' to say that DNS is trusted to securely canonicalize the name of the host you're connecting to. If it's ''no'', the hostname you typed on the command line gets passed untouched to the GSSAPI library. Default is ''no''. Optional, type uniline.

🍓 GSSAPIKexAlgorithms

The list of key exchange algorithms offered for GSSAPI key exchange. Possible values are gss-gex-sha1-, gss-group1-sha1-, gss-group14-sha1-, gss-group14-sha256-, gss-group16-sha512-, gss-nistp256-sha256-, gss-curve25519-sha256-.

The default is ''gss-group14-sha256-, gss-group16-sha512-, gss-nistp256-sha256-, gss-curve25519-sha256-, gss-gex-sha1-, gss-group14-sha1-''. This option only applies to connections using GSSAPI. Optional, type uniline.

💀 HashKnownHosts

Tells ssh(1) that it should hash host names and addresses when they get added to ~/.ssh/known_hosts. These hashed names work totally normally with ssh(1) and sshd(8), but they don't visually reveal identifying info if the file's contents get disclosed. Default is no.

Heads up bestie: existing names and addresses in known hosts files will not be converted automatically, but you can manually hash them using ssh-keygen1. Also, using this option may break facilities like tab-completion that rely on being able to read unhashed host names from ~/.ssh/known_hosts.

Optional, type boolean.

upstream_default value :
    no

🔥 HostbasedAcceptedAlgorithms

Specifies the signature algorithms that will be used for hostbased authentication, as a comma-separated list of patterns. But wait, there's more — alternates:

  • If the specified list begins with a '+' character, then the specified signature algorithms will be appended to the default set instead of replacing them.
  • If the specified list begins with a '-' character, then the specified signature algorithms (including wildcards) will be removed from the default set instead of replacing them.
  • If the specified list begins with a '^' character, then the specified signature algorithms will be placed at the head of the default set.

The default for this option is: ssh-ed25519-cert-v01@openssh.com, ecdsa-sha2-nistp256-cert-v01@openssh.com, ecdsa-sha2-nistp384-cert-v01@openssh.com, ecdsa-sha2-nistp521-cert-v01@openssh.com, sk-ssh-ed25519-cert-v01@openssh.com, sk-ecdsa-sha2-nistp256-cert-v01@openssh.com, rsa-sha2-512-cert-v01@openssh.com, rsa-sha2-256-cert-v01@openssh.com, ssh-ed25519, ecdsa-sha2-nistp256, ecdsa-sha2-nistp384, ecdsa-sha2-nistp521, sk-ssh-ed25519@openssh.com, sk-ecdsa-sha2-nistp256@openssh.com, rsa-sha2-512, rsa-sha2-256

The -Q option of ssh(1) may be used to list supported signature algorithms. This was formerly named HostbasedKeyTypes. Optional, type uniline.

Note: HostbasedAcceptedAlgorithms is migrated with '$old' and with: - $old => "- HostbasedKeyTypes"

🫶 HostbasedAuthentication

Specifies whether to try rhosts based authentication with public key authentication. The argument must be yes or no (the default). Optional, type boolean.

upstream_default value :
    no

🌟 HostKeyAlgorithms

Specifies the host key signature algorithms the client wants to use, in order of preference. And yes, the alternates are back, bestie:

  • If the specified list begins with a '+' character, then the specified signature algorithms will be appended to the default set instead of replacing them.
  • If the specified list begins with a '-' character, then the specified signature algorithms (including wildcards) will be removed from the default set instead of replacing them.
  • If the specified list begins with a '^' character, then the specified signature algorithms will be placed at the head of the default set.

The default for this option is: ssh-ed25519-cert-v01@openssh.com, ecdsa-sha2-nistp256-cert-v01@openssh.com, ecdsa-sha2-nistp384-cert-v01@openssh.com, ecdsa-sha2-nistp521-cert-v01@openssh.com, sk-ssh-ed25519-cert-v01@openssh.com, sk-ecdsa-sha2-nistp256-cert-v01@openssh.com, rsa-sha2-512-cert-v01@openssh.com, rsa-sha2-256-cert-v01@openssh.com, ssh-ed25519, ecdsa-sha2-nistp256, ecdsa-sha2-nistp384, ecdsa-sha2-nistp521, sk-ecdsa-sha2-nistp256@openssh.com, sk-ssh-ed25519@openssh.com, rsa-sha2-512, rsa-sha2-256

If hostkeys are known for the destination host, then this default is modified to prefer their algorithms.

The list of available signature algorithms may also be obtained using Qq ssh -Q HostKeyAlgorithms. Optional, type uniline.

🎀 HostKeyAlias

Specifies an alias that should be used instead of the real host name when looking up or saving the host key in the host key database files, and when validating host certificates. This option is useful for tunneling SSH connections, or for multiple servers running on a single host. Optional, type uniline.

💜 Hostname

Specifies the real host name to log into. You can use this to specify nicknames or abbreviations for hosts. Arguments to Hostname accept the tokens described in the TOKENS section. Numeric IP addresses are also permitted (both on the command line and in Hostname specifications). The default is the name given on the command line. Optional, type uniline.

🙈 IdentitiesOnly

Specifies that ssh(1) should only use the configured authentication identity and certificate files — either the default files, or those explicitly configured in the ssh_config files, or those passed on the ssh(1) command-line — even if ssh-agent1 or a PKCS11Provider or SecurityKeyProvider offers more identities. The argument to this keyword must be yes or no (the default). This option is intended for situations where ssh-agent offers many different identities. Optional, type boolean.

upstream_default value :
    no

🌸 IdentityAgent

Specifies the UNIX socket used to communicate with the authentication agent.

This option overrides the SSH_AUTH_SOCK environment variable and can be used to select a specific agent. Setting the socket name to none disables the use of an authentication agent. If the string Qq SSH_AUTH_SOCK is specified, the location of the socket will be read from the SSH_AUTH_SOCK environment variable. Otherwise, if the specified value begins with a '$' character, then it will be treated as an environment variable containing the location of the socket.

Arguments to IdentityAgent may use the tilde syntax to refer to a user's home directory, the tokens described in the TOKENS section, and environment variables as described in the ENVIRONMENT VARIABLES section. Optional, type uniline.

🦋 IdentityFile

Specifies a file from which the user's ECDSA, authenticator-hosted ECDSA, Ed25519, authenticator-hosted Ed25519 or RSA authentication identity is read. You can also specify a public key file to use the corresponding private key that is loaded in ssh-agent1 when the private key file isn't present locally. The default is ~/.ssh/id_rsa, ~/.ssh/id_ecdsa, ~/.ssh/id_ecdsa_sk, ~/.ssh/id_ed25519 and ~/.ssh/id_ed25519_sk. Additionally, any identities represented by the authentication agent will be used for authentication unless IdentitiesOnly is set. If no certificates have been explicitly specified by CertificateFile, ssh(1) will try to load certificate information from the filename obtained by appending -cert.pub to the path of a specified IdentityFile.

Arguments to IdentityFile may use the tilde syntax to refer to a user's home directory, or the tokens described in the TOKENS section. Alternately, an argument of none may be used to indicate no identity files should be loaded.

It is possible to have multiple identity files specified in configuration files; all these identities will be tried in sequence. Multiple IdentityFile directives will add to the list of identities tried (this behaviour differs from that of other configuration directives).

IdentityFile may be used in conjunction with IdentitiesOnly to select which identities in an agent are offered during authentication. IdentityFile may also be used in conjunction with CertificateFile in order to provide any certificate also needed for authentication with the identity. Optional, type list of uniline.

🌈 IgnoreUnknown

Specifies a pattern-list of unknown options to be ignored if they're encountered in configuration parsing. This may be used to suppress errors if ssh_config contains options that are unrecognised by ssh(1). It is recommended that IgnoreUnknown be listed early in the configuration file, as it will not be applied to unknown options that appear before it. Optional, type uniline.

Include 🎀

Okay so this one is the "go read that other file too" button. Include pulls in the configuration file(s) you point it at. You can list multiple pathnames, and each one can have glob(7) wildcards, tokens (the ones from the TOKENS section), environment variables (ENVIRONMENT VARIABLES section), and — for user configs only — shell-style ~ references to home directories. Wildcards get expanded and processed in lexical order. If a path isn't absolute, it's assumed to live in ~/.ssh when you're including from a user config file, or /etc/ssh when you're including from the system config file. And yes, Include can chill inside a Match or Host block for conditional inclusion, because it's flexible like that. Optional. Type list of uniline.

IPQoS 🌈

Sets the Differentiated Services Field Codepoint (DSCP) value for your connections. Accepted values are af11 af12 af13 af21 af22 af23 af31 af32 af33 af41 af42 af43 cs0 cs1 cs2 cs3 cs4 cs5 cs6 cs7 ef le, a numeric value, or none to just use whatever the operating system default is. This option takes one or two arguments, separated by whitespace. One argument means it's used as the packet class unconditionally. Two arguments means the first is auto-selected for interactive sessions and the second for non-interactive ones. The default is ef (Expedited Forwarding) for interactive sessions and none (operating system default) for non-interactive sessions. Optional. Type uniline.

KbdInteractiveAuthentication ⌨️

Do we use keyboard-interactive authentication, bestie? The argument has to be yes (the default) or no. Also heads up: ChallengeResponseAuthentication is a deprecated alias for this. Optional. Type boolean.

upstream_default value :

yes

KbdInteractiveDevices 💅

The list of methods to use in keyboard-interactive authentication. Multiple method names must be comma-separated. The default is to use the server's specified list. Which methods exist depends on what the server supports — for an OpenSSH server it might be zero or more of: bsdauth and pam. Optional. Type list of uniline.

KexAlgorithms 🔐

Specifies which KEX (Key Exchange) algorithms are allowed and in what preference order. The winner is the first algorithm in your list that the server also supports. Multiple algorithms must be comma-separated.

Now the fun part — the prefixes:

  • If the list starts with a '+' character, your algorithms get appended to the default set instead of replacing it.
  • If it starts with a '-' character, your algorithms (wildcards included!) get removed from the default set instead of replacing it.
  • If it starts with a '^' character, your algorithms get placed at the head of the default set.

The default is: mlkem768x25519-sha256, sntrup761x25519-sha512, sntrup761x25519-sha512@openssh.com, curve25519-sha256, curve25519-sha256@libssh.org, ecdh-sha2-nistp256, ecdh-sha2-nistp384, ecdh-sha2-nistp521, diffie-hellman-group-exchange-sha256, diffie-hellman-group16-sha512, diffie-hellman-group18-sha512, diffie-hellman-group14-sha256

You can also just ask for the list of supported key exchange algorithms with ssh -Q kex. Optional. Type uniline.

KnownHostsCommand 🔍

Specifies a command to use to get a list of host keys, on top of the ones listed in UserKnownHostsFile and GlobalKnownHostsFile. This command runs after the files have been read. It can write host key lines to standard output in the exact same format as the usual files (described in the VERIFYING HOST KEYS section in ssh(1)). Arguments to KnownHostsCommand accept the tokens from the TOKENS section. The command may get invoked multiple times per connection: once when preparing the preference list of host key algorithms, again to grab the host key for the requested host name, and — if CheckHostIP is enabled — one more time to get the host key matching the server's address. If the command exits abnormally or returns a non-zero exit status, the connection is terminated. Optional. Type uniline.

LocalCommand 🏠

Specifies a command to run on the local machine after successfully connecting to the server. The command string runs to the end of the line and is executed with the user's shell. Arguments to LocalCommand accept the tokens from the TOKENS section.

Heads up bestie: the command runs synchronously and does not have access to the session of the ssh(1) that spawned it. So don't use it for interactive commands, fr fr.

Also, this directive is ignored unless PermitLocalCommand has been enabled. Optional. Type uniline.

LocalForward 🚇

Specifies that a TCP port or Unix-domain socket on the local machine gets forwarded over the secure channel to the specified host and port (or Unix-domain socket) on the remote machine. For a TCP port, the first argument must be [bind_address:]port or a Unix domain socket path. The second argument is the destination and may be host:hostport or a Unix domain socket path if the remote host supports it.

IPv6 addresses go in square brackets, okay?

If either argument contains a '/' in it, that argument is interpreted as a Unix-domain socket (on the corresponding host) instead of a TCP port.

You can specify multiple forwardings, and additional ones can be given on the command line. Only the superuser can forward privileged ports. By default the local port is bound in accordance with the GatewayPorts setting. But an explicit bind_address can be used to bind the connection to a specific address. A bind_address of localhost means the listening port is bound for local use only, while an empty address or '*' means the port should be available from all interfaces. Unix domain socket paths may use the tokens from the TOKENS section and environment variables from the ENVIRONMENT VARIABLES section. Optional. Type list of node of class Ssh::PortForward.

LogLevel 📢

Sets the verbosity level used when logging messages from ssh(1). Possible values are: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO. DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify higher levels of verbose output. Optional. Type enum. choice: 'DEBUG', 'DEBUG1', 'DEBUG2', 'DEBUG3', 'ERROR', 'FATAL', 'INFO', 'QUIET', 'VERBOSE'.

upstream_default value :

INFO

LogVerbose 🗣️

Specify one or more overrides to LogLevel. An override is made of one or more pattern lists that match the source file, function and line number, forcing detailed logging for that spot. Example — an override pattern of:

kex.c:*:1000,*:kex_exchange_identification():*,packet.c:*

would enable detailed logging for line 1000 of kex.c, everything in the kex_exchange_identification() function, and all code in the packet.c file. This option is intended for debugging and no overrides are enabled by default. Optional. Type uniline.

MACs 🛡️

Specifies the MAC (message authentication code) algorithms in order of preference. The MAC algorithm handles data integrity protection. Multiple algorithms must be comma-separated. Same prefix energy as before:

  • If the list starts with a '+' character, your algorithms get appended to the default set instead of replacing it.
  • If it starts with a '-' character, your algorithms (wildcards included) get removed from the default set instead of replacing it.
  • If it starts with a '^' character, your algorithms get placed at the head of the default set.

The algorithms containing -etm calculate the MAC after encryption (encrypt-then-mac). Those are considered safer and their use is recommended. 👑

The default is: umac-64-etm@openssh.com, umac-128-etm@openssh.com, hmac-sha2-256-etm@openssh.com, hmac-sha2-512-etm@openssh.com, hmac-sha1-etm@openssh.com, umac-64@openssh.com, umac-128@openssh.com, hmac-sha2-256, hmac-sha2-512, hmac-sha1

The list of available MAC algorithms may also be obtained using ssh -Q mac. Optional. Type uniline.

NoHostAuthenticationForLocalhost 🏡

Disable host authentication for localhost (loopback addresses). The argument to this keyword must be yes or no (the default). Optional. Type boolean.

upstream_default value :

no

NumberOfPasswordPrompts 🔢

Specifies the number of password prompts before giving up. The argument to this keyword must be an integer. The default is 3. Optional. Type integer.

upstream_default value :

3

ObscureKeystrokeTiming 🙈

Specifies whether ssh(1) should try to obscure inter-keystroke timings from passive observers of network traffic. If enabled, then for interactive sessions, ssh(1) will send keystrokes at fixed intervals of a few tens of milliseconds and will send fake keystroke packets for some time after typing ceases. The argument to this keyword must be yes, no, or an interval specifier of the form interval:milliseconds (e.g. interval:80 for 80 milliseconds). The default is to obscure keystrokes using a 20ms packet interval. Note that smaller intervals will result in higher fake keystroke packet rates. Optional. Type uniline.

upstream_default value :

interval:20

PasswordAuthentication 🔑

Specifies whether to use password authentication. The argument to this keyword must be yes (the default) or no. Optional. Type boolean.

upstream_default value :

yes

PermitLocalCommand ⚡

Allow local command execution via the LocalCommand option or by using the ! command escape sequence in ssh(1). The argument must be yes or no (the default). Optional. Type boolean.

upstream_default value :

no

PermitRemoteOpen 🚪

Specifies the destinations to which remote TCP port forwarding is permitted when RemoteForward is used as a SOCKS proxy. The forwarding specification must be one of these forms:

PermitRemoteOpen host:port
PermitRemoteOpen IPv4_addr:port
PermitRemoteOpen [IPv6_addr]:port

Multiple forwards can be specified by separating them with whitespace. An argument of any removes all restrictions and permits any forwarding requests. An argument of none prohibits all forwarding requests. The wildcard '*' can be used for host or port to allow all hosts or ports respectively. Otherwise, no pattern matching or address lookups are performed on supplied names. Optional. Type list of uniline.

PKCS11Provider 🔏

Specifies which PKCS#11 provider to use, or none to indicate that no provider should be used (the default). The argument to this keyword is a path to the PKCS#11 shared library ssh(1) should use to communicate with a PKCS#11 token providing keys for user authentication. Optional. Type uniline.

🚪 Port

Tells it which port to knock on when it's hitting up the remote host. Default is 22 — the classic. Optional. Type uniline.

🔐 PreferredAuthentications

This one's the ~vibe check~ for auth methods: it sets the order the client tries them in. So a client can stan one method over another (like preferring keyboard-interactive over password, iykyk). Default is: gssapi-with-mic, hostbased, publickey, keyboard-interactive, password. Optional. Type list of uniline.

🛰️ ProxyCommand

Specifies the command used to connect to the server. Heads up bestie — the command string runs all the way to the end of the line, and it gets executed using the user's shell exec directive so you don't end up with a lingering shell process just vibing in the background.

Arguments to ProxyCommand accept the tokens described in the TOKENS section. The command can be basically anything, and it should read from its standard input and write to its standard output. It should eventually connect to an sshd(8) server running on some machine, or execute sshd -i somewhere. Host key management gets handled using the Hostname of the host being connected (defaulting to whatever name the user typed in). Setting the command to none disables this option entirely. Also note: CheckHostIP is not available for connects with a proxy command.

This directive is super useful alongside nc(1) and its proxy support. For example, this directive would connect via an HTTP proxy at 192.0.2.0:

ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p

Optional. Type uniline.

🦘 ProxyJump

Specifies one or more jump proxies, written as either [user @] host [: port] or as an ssh URI. Multiple proxies can be separated by comma characters and will be visited sequentially (a lil relay race 💫). Setting this option makes ssh(1) connect to the target host by first making an ssh(1) connection to the specified ProxyJump host and then establishing a TCP forwarding to the ultimate target from there. Setting the host to none disables this option entirely.

Heads up: this option will compete with the ProxyCommand option — whichever one is specified first will prevent later instances of the other from taking effect. No sharing, bestie.

Also note: the configuration for the destination host (whether it came from the command line or the configuration file) is not generally applied to jump hosts. ~/.ssh/config should be used if you need specific config for jump hosts. Optional. Type list of uniline.

🎁 ProxyUseFdpass

Says that ProxyCommand will pass a connected file descriptor back to ssh(1) instead of continuing to execute and pass data. Default is no. Optional. Type boolean.

upstream_default value:

no

🗝️ PubkeyAcceptedAlgorithms

Specifies the signature algorithms used for public key authentication, as a comma-separated list of patterns. Okay so the rules here are giving ✨choose your own adventure✨:

  • If the list begins with a + character, the algorithms after it get appended to the default instead of replacing it.
  • If the list begins with a - character, the specified algorithms (wildcards included) get removed from the default set instead of replacing them.
  • If the list begins with a ^ character, the specified algorithms get placed at the head of the default set.

The default for this option is:

ssh-ed25519-cert-v01@openssh.com,
ecdsa-sha2-nistp256-cert-v01@openssh.com,
ecdsa-sha2-nistp384-cert-v01@openssh.com,
ecdsa-sha2-nistp521-cert-v01@openssh.com,
sk-ssh-ed25519-cert-v01@openssh.com,
sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
rsa-sha2-512-cert-v01@openssh.com, rsa-sha2-256-cert-v01@openssh.com,
ssh-ed25519, ecdsa-sha2-nistp256, ecdsa-sha2-nistp384,
ecdsa-sha2-nistp521, sk-ssh-ed25519@openssh.com,
sk-ecdsa-sha2-nistp256@openssh.com, rsa-sha2-512, rsa-sha2-256

The list of available signature algorithms can also be obtained using ssh -Q PubkeyAcceptedAlgorithms. Optional. Type uniline.

Note: PubkeyAcceptedAlgorithms is migrated with '$old' and with:

  • $old => "- PubkeyAcceptedKeyTypes"

🔑 PubkeyAuthentication

Specifies whether to try public key authentication. The argument to this keyword must be yes (the default), no, unbound or host-bound. The final two options enable public key authentication while respectively disabling or enabling the OpenSSH host-bound authentication protocol extension required for restricted ssh-agent forwarding. Optional. Type enum. choice: 'host-bound', 'no', 'unbound', 'yes'.

upstream_default value:

yes

🙅 RefuseConnection

Lets a connection be refused by the configuration file itself, iconic. If this option is specified, then ssh(1) will terminate immediately before even attempting to connect to the remote host, display an error message containing the argument to this keyword, and return a non-zero exit status. This one's handy for expressing reminders or warnings to the user via ssh_config. Optional. Type uniline.

🔄 RekeyLimit

Specifies the maximum amount of data that may be transmitted or received before the session key gets renegotiated, optionally followed by a maximum amount of time that may pass before the session key is renegotiated. The first argument is specified in bytes and can have a suffix of 'K', 'M' or 'G' to mean Kilobytes, Megabytes, or Gigabytes, respectively. The default is between '1G' and '4G' depending on the cipher. The optional second value is specified in seconds and can use any of the units documented in the TIME FORMATS section of sshd_config(5). The default value for RekeyLimit is default none, which means rekeying happens after the cipher's default amount of data has been sent or received and no time-based rekeying is done. Optional. Type uniline.

💻 RemoteCommand

Specifies a command to execute on the remote machine after successfully connecting to the server. The command string runs to the end of the line, and is executed with the user's shell. Arguments to RemoteCommand accept the tokens described in the TOKENS section. Optional. Type uniline.

📡 RemoteForward

Specifies that a TCP port or Unix-domain socket on the remote machine be forwarded over the secure channel. The remote port can either be forwarded to a specified host and port or Unix-domain socket from the local machine, or it can act as a SOCKS 4/5 proxy that lets a remote client connect to arbitrary destinations from the local machine.

The first argument is the listening specification and may be [bind_address : port] or, if the remote host supports it, a Unix domain socket path. If forwarding to a specific destination, then the second argument must be host : hostport or a Unix domain socket path. Otherwise, if no destination argument is specified, then the remote forwarding will be established as a SOCKS proxy. When acting as a SOCKS proxy, the destination of the connection can be restricted by PermitRemoteOpen.

IPv6 addresses can be specified by enclosing addresses in square brackets.

If either argument contains a '/' in it, that argument gets interpreted as a Unix-domain socket (on the corresponding host) rather than a TCP port.

Multiple forwardings can be specified, and additional forwardings can be given on the command line. Privileged ports can only be forwarded when logging in as root on the remote machine. Unix domain socket paths may use the tokens described in the TOKENS section and environment variables as described in the ENVIRONMENT VARIABLES section.

If the port argument is 0, the listen port will be dynamically allocated on the server and reported to the client at run time.

If the bind_address is not specified, the default is to only bind to loopback addresses. If the bind_address is '*' or an empty string, then the forwarding is requested to listen on all interfaces. Specifying a remote bind_address will only succeed if the server's GatewayPorts option is enabled (see sshd_config(5)). Optional. Type list of node of class Ssh::PortForward.

🖥️ RequestTTY

Specifies whether to request a pseudo-tty for the session. The argument can be one of: no (never request a TTY), yes (always request a TTY when standard input is a TTY), force (always request a TTY) or auto (request a TTY when opening a login session). This option mirrors the -t and -T flags for ssh(1). Optional. Type enum. choice: 'auto', 'force', 'no', 'yes'.

📏 RequiredRSASize

Specifies the minimum RSA key size (in bits) that ssh(1) will accept. User authentication keys smaller than this limit will be ignored. Servers that present host keys smaller than this limit will cause the connection to be terminated. The default is 1024 bits. Note that this limit may only be raised from the default. Optional. Type integer.

upstream_default value:

1024

🚫 RevokedHostKeys

Specifies revoked host public keys. Keys listed in this file will be refused for host authentication. Big warning though: if this file doesn't exist or isn't readable, then host authentication will be refused for all hosts. Keys can be specified as a text file listing one public key per line, or as an OpenSSH Key Revocation List (KRL) as generated by ssh-keygen(1). For more info on KRLs, see the KEY REVOCATION LISTS section in ssh-keygen(1). Arguments to RevokedHostKeys may use the tilde syntax to refer to a user's home directory, the tokens described in the TOKENS section, and environment variables as described in the ENVIRONMENT VARIABLES section. Optional. Type uniline.

🔒 SecurityKeyProvider

Specifies a path to a library that will be used when loading any FIDO authenticator-hosted keys, overriding the default of using the built-in USB HID support.

If the specified value begins with a '$' character, then it will be treated as an environment variable containing the path to the library. Optional. Type uniline.

📤 SendEnv

Specifies what variables from the local environ(7) should be sent to the server. The server must also support it, and the server must be configured to accept these environment variables. Note that the TERM environment variable is always sent whenever a pseudo-terminal is requested, since it's required by the protocol. Refer to AcceptEnv in sshd_config(5) for how to configure the server. Variables are specified by name, which may contain wildcard characters. Multiple environment variables can be separated by whitespace or spread across multiple SendEnv directives.

See PATTERNS for more info on patterns.

It's possible to clear previously set SendEnv variable names by prefixing patterns with -. The default is not to send any environment variables. Optional. Type list of uniline.

🌸 ServerAliveCountMax 🌸

Okay bestie, so this one sets the number of server alive messages (see below, iykyk) that can be sent without ssh(1) receiving any messages back from the server. If this threshold gets reached while server alive messages are being sent, ssh will disconnect from the server and terminate the session, periodt. And it is important to note that the use of server alive messages is very different from TCPKeepAlive (below). The server alive messages are sent through the encrypted channel, so they will not be spoofable. Meanwhile the TCP keepalive option enabled by TCPKeepAlive is spoofable. The server alive mechanism is valuable when the client or server depend on knowing when a connection has become unresponsive. Like, it's giving "are you still there?" energy.

The default value is 3. So if, for example, ServerAliveInterval (see below) is set to 15 and ServerAliveCountMax is left at the default, if the server becomes unresponsive, ssh will disconnect after approximately 45 seconds. Optional. Type integer.

upstream_default value :
    3

✨ ServerAliveInterval ✨

Sets a timeout interval in seconds after which, if no data has been received from the server, ssh(1) will send a message through the encrypted channel to request a response from the server. The default is 0, indicating that these messages will not be sent to the server, or 300 if the BatchMode option is set (Debian-specific). ProtocolKeepAlives is a Debian-specific compatibility alias for this option. Optional. Type integer.

upstream_default value :
    0

💅 SessionType 💅

May be used to either request invocation of a subsystem on the remote system, or to prevent the execution of a remote command at all. The latter is useful for just forwarding ports — no shell, just vibes. The argument to this keyword must be none (same as the -N option), subsystem (same as the -s option) or default (shell or command execution). Optional. Type enum. choice: 'default', 'none', 'subsystem'.

🎀 SetEnv 🎀

Directly specify one or more environment variables and their contents to be sent to the server in the form ''NAME=VALUE'' Similarly to SendEnv with the exception of the TERM variable, the server must be prepared to accept the environment variable. So like, don't just yeet random vars at it, the server has to be ready.

The ''VALUE'' may use the tokens described in the TOKENS section and environment variables as described in the ENVIRONMENT VARIABLES section. Optional. Type uniline.

🌈 StdinNull 🌈

Redirects stdin from /dev/null (actually, prevents reading from stdin). Either this or the equivalent -n option must be used when ssh is run in the background. The argument to this keyword must be yes (same as the -n option) or no (the default). Optional. Type boolean.

upstream_default value :
    no

🦋 StreamLocalBindMask 🦋

Sets the octal file creation mode mask (umask) used when creating a Unix-domain socket file for local or remote port forwarding. This option is only used for port forwarding to a Unix-domain socket file. So if you're not doing that, this is not the one, bestie.

The default value is 0177, which creates a Unix-domain socket file that is readable and writable only by the owner. Note that not all operating systems honor the file mode on Unix-domain socket files. Optional. Type uniline.

Specifies whether to remove an existing Unix-domain socket file for local or remote port forwarding before creating a new one. If the socket file already exists and StreamLocalBindUnlink is not enabled, ssh will be unable to forward the port to the Unix-domain socket file. This option is only used for port forwarding to a Unix-domain socket file.

The argument must be yes or no (the default). Optional. Type boolean.

upstream_default value :
    no

👑 StrictHostKeyChecking 👑

If this flag is set to yes, ssh(1) will never automatically add host keys to the ~/.ssh/known_hosts file, and refuses to connect to hosts whose host key has changed. This provides maximum protection against man-in-the-middle (MITM) attacks, though it can be annoying when the /etc/ssh/ssh_known_hosts file is poorly maintained or when connections to new hosts are frequently made. This option forces the user to manually add all new hosts. So it's highkey secure but also highkey annoying sometimes.

If this flag is set to accept-new then ssh will automatically add new host keys to the user's known_hosts file, but will not permit connections to hosts with changed host keys. If this flag is set to no or off, ssh will automatically add new host keys to the user known hosts files and allow connections to hosts with changed hostkeys to proceed, subject to some restrictions. If this flag is set to ask (the default), new host keys will be added to the user known host files only after the user has confirmed that is what they really want to do, and ssh will refuse to connect to hosts whose host key has changed. The host keys of known hosts will be verified automatically in all cases. Optional. Type enum. choice: 'yes', 'accept-new', 'no', 'off', 'ask'.

upstream_default value :
    ask

💖 SyslogFacility 💖

Gives the facility code that is used when logging messages from ssh(1). The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. The default is USER. Optional. Type enum. choice: 'AUTH', 'DAEMON', 'LOCAL0', 'LOCAL1', 'LOCAL2', 'LOCAL3', 'LOCAL4', 'LOCAL5', 'LOCAL6', 'LOCAL7', 'USER'.

upstream_default value :
    USER

🔥 TCPKeepAlive 🔥

Specifies whether the system should send TCP keepalive messages to the other side. If they are sent, death of the connection or crash of one of the machines will be properly noticed. This option only uses TCP keepalives (as opposed to using ssh level keepalives), so it takes a long time to notice when the connection dies. As such, you probably want the ServerAliveInterval option as well. However, this means that connections will die if the route is down temporarily, and some people find it annoying. Like, pick your fighter, bestie.

The default is yes (to send TCP keepalive messages), and the client will notice if the network goes down or the remote host dies. This is important in scripts, and many users want it too.

To disable TCP keepalive messages, the value should be set to no. See also ServerAliveInterval for protocol-level keepalives. Optional. Type boolean.

upstream_default value :
    yes

🏷️ Tag 🏷️

Specify a configuration tag name that may be later used by a Match directive to select a block of configuration. Optional. Type uniline.

🚇 Tunnel 🚇

Request tun(4) device forwarding between the client and the server. The argument must be yes, point-to-point (layer 3), ethernet (layer 2), or no (the default). Specifying yes requests the default tunnel mode, which is point-to-point. Optional. Type enum. choice: 'ethernet', 'no', 'point-to-point', 'yes'.

upstream_default value :
    no

🛤️ TunnelDevice 🛤️

Specifies the tun(4) devices to open on the client (local_tun ) and the server (remote_tun ).

The argument must be local_tun [: remote_tun ] The devices may be specified by numerical ID or the keyword any, which uses the next available tunnel device. If remote_tun is not specified, it defaults to any. The default is any:any. Optional. Type uniline.

upstream_default value :
    any:any

🔑 UpdateHostKeys 🔑

Specifies whether ssh(1) should accept notifications of additional hostkeys from the server sent after authentication has completed and add them to UserKnownHostsFile. The argument must be yes, no, or ask. This option allows learning alternate hostkeys for a server and supports graceful key rotation by allowing a server to send replacement public keys before old ones are removed. So it's like a glow-up for your host keys.

Additional hostkeys are only accepted if the key used to authenticate the host was already trusted or explicitly accepted by the user, the host was authenticated via UserKnownHostsFile (i.e. not GlobalKnownHostsFile, and the host was authenticated using a plain key and not a certificate).

UpdateHostKeys is enabled by default if the user has not overridden the default UserKnownHostsFile setting and has not enabled VerifyHostKeyDNS; otherwise UpdateHostKeys will be set to no.

If UpdateHostKeys is set to ask, then the user is asked to confirm the modifications to the known_hosts file. Confirmation is currently incompatible with ControlPersist and will be disabled if it is enabled.

Presently, only sshd(8) from OpenSSH 6.8 and greater support the Qq hostkeys@openssh.com protocol extension used to inform the client of all the server's hostkeys. Optional. Type enum. choice: 'ask', 'no', 'yes'.

👤 User 👤

Specifies the user to log in as. This can be useful when a different user name is used on different machines. This saves the trouble of having to remember to give the user name on the command line. Arguments to User may use the tokens described in the TOKENS section (with the exception of %r and %C) and environment variables as described in the ENVIRONMENT VARIABLES section. Optional. Type uniline.

📁 UserKnownHostsFile 📁

Specifies one or more files to use for the user host key database, separated by whitespace. Each filename may use tilde notation to refer to the user's home directory, the tokens described in the TOKENS section and environment variables as described in the ENVIRONMENT VARIABLES section. A value of none causes ssh(1) to ignore any user-specific known hosts files. The default is ~/.ssh/known_hosts ~/.ssh/known_hosts2. Optional. Type list of uniline.

🌐 VerifyHostKeyDNS 🌐

Specifies whether to verify the remote key using DNS and SSHFP resource records. If this option is set to yes, the client will implicitly trust keys that match a secure fingerprint from DNS. Insecure fingerprints will be handled as if this option was set to ask. If this option is set to ask, information on fingerprint match will be displayed, but the user will still need to confirm new host keys according to the StrictHostKeyChecking option. The default is no.

See also VERIFYING HOST KEYS in ssh(1). Optional. Type enum. choice: 'ask', 'no', 'yes'.

upstream_default value :
    no

📝 VersionAddendum 📝

Optionally specifies additional text to append to the SSH protocol banner sent by the client upon connection. The default is none. Optional. Type uniline.

🎨 VisualHostKey 🎨

If this flag is set to yes, an ASCII art representation of the remote host key fingerprint is printed in addition to the fingerprint string at login and for unknown host keys. If this flag is set to no (the default), no fingerprint strings are printed at login and only the fingerprint string will be printed for unknown host keys. Optional. Type uniline.

upstream_default value :
    no
  • WarnWeakCrypto 💅 — this one controls whether you get warned when the crypto algorithms negotiated for the connection are weak or otherwise recommended against. You can mute warnings two ways: turn off one specific warning, or turn off all of them. Warnings about connections that don't use a post-quantum key exchange get silenced with the no-pq-kex flag. no disables all the warnings. The default is equivalent to yes, which enables all warnings. Optional. Type uniline.
  • XAuthLocation 🎀 — specifies the full pathname of the xauth(1) program. Default is /usr/bin/xauth. Optional. Type uniline.
    • upstream_default value: /usr/bin/xauth
  • FallBackToRsh 💀 — this parameter is now ignored by Ssh. Deprecated. Optional. Type uniline.
  • HostbasedKeyTypes 💀 — this parameter is now ignored by Ssh. Deprecated. Optional. Type uniline.
  • PubkeyAcceptedKeyTypes 💀 — this parameter is now ignored by Ssh. Deprecated. Optional. Type uniline.
  • UseRsh 💀 — this parameter is now ignored by Ssh. Deprecated. Optional. Type uniline.
  • Match 👑 — restricts the following declarations (up to the next Host or Match keyword) so they only apply when the conditions after the Match keyword are satisfied. Match conditions are given using one or more criteria, or the single token all, which always matches. The available criteria keywords are: canonical final exec localnetwork host originalhost tagged command user localuser and version. The all criteria has to appear alone, or immediately after canonical or final. Other criteria may be combined arbitrarily. All criteria except all, canonical and final require an argument. Criteria may be negated by prepending an exclamation mark (!).

The canonical keyword matches only when the configuration file is being re-parsed after hostname canonicalization — peep the CanonicalizeHostname option. This can be handy for specifying conditions that only work with canonical host names. ✨

The final keyword requests that the configuration be re-parsed (regardless of whether CanonicalizeHostname is enabled), and matches only during this final pass. If CanonicalizeHostname is enabled, then canonical and final match during the same pass.

The exec keyword executes the specified command under the user's shell. If the command returns a zero exit status then the condition counts as true. Commands containing whitespace characters must be quoted. Arguments to exec accept the tokens described in the TOKENS section. 🔥

The localnetwork keyword matches the addresses of active local network interfaces against the supplied list of networks in CIDR format. This may be convenient for varying the effective configuration on devices that roam between networks.

okay bestie, real talk 🙈 — the network address is not a trustworthy criteria in many situations (e.g. when the network is automatically configured using DHCP), so be careful if you're using it to control security-sensitive configuration.

The other keywords' criteria must be single entries or comma-separated lists, and may use the wildcard and negation operators described in the PATTERNS section.

The criteria for the host keyword are matched against the target hostname, after any substitution by the Hostname or CanonicalizeHostname options. The originalhost keyword matches against the hostname as it was specified on the command-line.

The tagged keyword matches a tag name specified by a prior Tag directive or on the ssh(1) command-line using the -P flag. The command keyword matches the remote command that has been requested, or the subsystem name that is being invoked (e.g. sftp for an SFTP session). The empty string will match the case where a command or tag has not been specified, i.e. Match tag . The version keyword matches against the version string of ssh(1), for example OpenSSH_10.0.

The user keyword matches against the target username on the remote host. The localuser keyword matches against the name of the local user running ssh(1) — this keyword may be useful in system-wide ssh_config files. 💜

Finally, the sessiontype keyword matches the requested session type, which may be one of shell for interactive sessions, exec for command execution sessions, subsystem for subsystem invocations such as sftp(1), or none for transport-only sessions, such as when ssh(1) is started with the -N flag. Optional. Type hash of node of class Ssh::HostElement.

🌈 SEE ALSO 🌈

  • cme
  • Config::Model::models::Ssh::HostElement
  • Config::Model::models::Ssh::PortForward

🎀 LICENSE 🎀

LGPL2

and that's the whole page, bestie, you made it to the end 🫶✨ go forth and configure your ssh, main character energy only. this masterpiece of a manual page is perl v5.40.1 coded up on 2025-10-26, and yeah the page header is literally just Config...s::Ssh(3pm) because it's so iconic it doesn't need a longer name 💅💖

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