SYSTEMD-SYSUSERS(8)

💖 SYSTEMD-SYSUSERS(8) 💖

okay bestie, gather round, because today we're talking about systemd-sysusers — aka the manual page systemd-sysusers — and honestly? it's giving "quietly keeping your whole system's user database cute and consistent" and I'm obsessed. 💅

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✨ NAME ✨

systemd-sysusers, systemd-sysusers.service — allocate system users and groups 🫶

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🌸 SYNOPSIS 🌸

systemd-sysusers [OPTIONS...] [CONFIGFILE...]

systemd-sysusers.service

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🦋 DESCRIPTION 🦋

so systemd-sysusers creates system users and groups, based on files in the format described in sysusers.d(5). no cap, that's the whole job. ✨

if you invoke it with no arguments, it applies all directives from all files found in the directories specified by sysusers.d(5).

when you invoke it with positional arguments, here's the tea: if the option --replace=PATH is specified, the arguments specified on the command line are used instead of the configuration file PATH. otherwise, just the configuration specified by the command line arguments is executed.

the string - may be specified instead of a filename to instruct systemd-sysusers to read the configuration from standard input. 🎀

if the argument is a relative path, all configuration directories are searched for a matching file, and the file found that has the highest priority is executed. if the argument is an absolute path, that file is used directly, without searching of the configuration directories. periodt. 💅

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💜 OPTIONS 💜

the following options are understood:

• --root=root — takes a directory path as an argument. All paths will be prefixed with the given alternate root path, including config search paths.
• --image=image — takes a path to a disk image file or block device node. if specified, all operations are applied to the file system in the indicated disk image. this is similar to --root= but operates on file systems stored in disk images or block devices. the disk image should either contain just a file system, or a set of file systems within a GPT partition table, following the Discoverable Partitions Specification[1]. for further information on supported disk images, see systemd-nspawn(1)'s switch of the same name. 🦋
• --replace=PATH — when this option is given, one or more positional arguments must be specified. all configuration files found in the directories listed in sysusers.d(5) will be read, and the configuration given on the command line will be handled instead of and with the same priority as the configuration file PATH.

this option is intended to be used when package installation scripts are running and files belonging to that package are not yet available on disk, so their contents must be given on the command line, but the admin configuration might already exist and should be given higher priority.

🎀 Example 1. RPM installation script for radvd 🎀

echo 'u radvd - "radvd daemon"' | \
          systemd-sysusers --replace=/usr/lib/sysusers.d/radvd.conf -

this will create the radvd user as if /usr/lib/sysusers.d/radvd.conf was already on disk. an admin might override the configuration specified on the command line by placing /etc/sysusers.d/radvd.conf or even /etc/sysusers.d/00-overrides.conf. 👑

note that this is the expanded form, and when used in a package, this would be written using a macro with "radvd" and a file containing the configuration line as arguments.

• --dry-run — process the configuration and figure out what entries would be created, but don't actually write anything. window shopping, basically. 🛍️
• --inline — treat each positional argument as a separate configuration line instead of a file name.
• --cat-config — copy the contents of config files to standard output. before each file, the filename is printed as a comment. 📄
• --no-pager — do not pipe output into a pager.
• -h, --help — print a short help text and exit.
• --version — print a short version string and exit.

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🔐 CREDENTIALS 🔐

systemd-sysusers supports the service credentials logic as implemented by LoadCredential=/SetCredential= (see systemd.exec(1) for details). the following credentials are used when passed in:

• "passwd.hashed-password.user" — a UNIX hashed password string to use for the specified user, when creating an entry for it. this is particularly useful for the "root" user, as it allows provisioning the default root password to use via a unit file drop-in or from a container manager passing in this credential. note that setting this credential has no effect if the specified user account already exists. this credential is hence primarily useful in first boot scenarios, or systems that are fully stateless and come up with an empty /etc/ on every boot. 🌱
• "passwd.plaintext-password.user" — similar to "passwd.hashed-password.user" but expects a literal, plaintext password, which is then automatically hashed before being used for the user account. if both the hashed and the plaintext credential are specified for the same user, the former takes precedence. it's generally recommended to specify the hashed version; however, in test environments with weaker requirements on security it might be easier to pass passwords in plaintext instead. 🙈
• "passwd.shell.user" — specifies the shell binary to use for the specified account when creating it. 🐚
• "sysusers.extra" — the contents of this credential may contain additional lines to operate on. the credential contents should follow the same format as any other sysusers.d/ drop-in. if this credential is passed, it is processed after all of the drop-in files read from the file system.

note that by default the systemd-sysusers.service unit file is set up to inherit the "passwd.hashed-password.root", "passwd.plaintext-password.root", "passwd.shell.root" and "sysusers.extra" credentials from the service manager. thus, when invoking a container with an unpopulated /etc/ for the first time, it is possible to configure the root user's password to be "systemd" like this:

# systemd-nspawn --image=... --set-credential=passwd.hashed-password.root:'$y$j9T$yAuRJu1o5HioZAGDYPU5d.$F64ni6J2y2nNQve90M/p0ZP0ECP/qqzipNyaY9fjGpC' ...

note again that the data specified in this credential is consulted only when creating an account for the first time — it may not be used for changing the password or shell of an account that already exists. like, it's a first-meeting thing, not a glow-up-your-existing-account thing. 😭

use mkpasswd(1) for generating UNIX password hashes from the command line. 🔥

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💀 EXIT STATUS 💀

on success, 0 is returned, a non-zero failure code otherwise. that's it, that's the vibe check.

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🌈 SEE ALSO 🌈

systemd(1), sysusers.d(5), Users, Groups, UIDs and GIDs on systemd systems[2], systemd.exec(1), mkpasswd(1)

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📝 NOTES 📝

1. Discoverable Partitions Specification — https://systemd.io/DISCOVERABLE_PARTITIONS
2. Users, Groups, UIDs and GIDs on systemd systems — https://systemd.io/UIDS-GIDS

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and that's the whole page, bestie!! 💖 this one's from systemd 238.51, and yeah, it's SYSTEMD-SYSUSERS(8) — go make some users, drink water, and don't forget to --dry-run first. mwah 🫶🎀✨