RUNUSER(1)

✨ RUNUSER(1) ✨

okay bestie, gather round, because this is the runuser manual page from User Commands and it's literally the moment 💅

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🌸 NAME 🌸

runuser — run a command with substitute user and group ID

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🦋 SYNOPSIS 🦋

runuser [options] -u user [[--] command [argument...]]

runuser [options] [-] [user [argument...]]

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💖 DESCRIPTION 💖

So runuser lets you run commands with a substitute user and group ID. Iconic behavior, no cap.

If you don't pass the -u option, runuser falls back to su-compatible semantics and just executes a shell. The glow-up difference between runuser and su? runuser does not ask for a password (because it may only be executed by the root user) and it uses a different PAM configuration. Also, runuser does not have to be installed with set-user-ID permissions. She's low-maintenance like that. 👑

If the PAM session isn't required, then the recommended solution is to use the setpriv(1) command instead. Noted, bestie.

When called without arguments, runuser defaults to running an interactive shell as root. main character energy fr fr.

For backward compatibility, runuser defaults to not changing the current directory and to setting only the environment variables HOME and SHELL (plus USER and LOGNAME if the target user is not root). This version of runuser uses PAM for session management.

Heads up: runuser in all cases uses PAM (pam_getenvlist(3)) to do the final environment modification. Command-line options such as --login and --preserve-environment affect the environment before it gets modified by PAM. Order matters, bestie. 🫶

Since version 2.38, runuser resets process resource limits RLIMIT_NICE, RLIMIT_RTPRIO, RLIMIT_FSIZE, RLIMIT_AS and RLIMIT_NOFILE. Spring cleaning behavior. ✨

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🎀 OPTIONS 🎀

• -c, --command=command — Pass command to the shell with the -c option. Creates a new session via setsid(2). Refer to --session-command to keep the same session.
• -f, --fast — Pass -f to the shell, which may or may not be useful, depending on the shell. It's giving "your mileage may vary" 💀
• -g, --group=group — The primary group to be used. This option is allowed for the root user only.
• -G, --supp-group=group — Specify a supplementary group. This option is available to the root user only. The first specified supplementary group is also used as a primary group if the option --group is not specified.
• -, -l, --login — Start the shell as a login shell with an environment similar to a real login:
  • clears all the environment variables except for TERM, COLORTERM, NO_COLOR and variables specified by --whitelist-environment
  • initializes the environment variables HOME, SHELL, USER, LOGNAME, and PATH
  • changes to the target user's home directory
  • sets argv[0] of the shell to '-' in order to make the shell a login shell
• -m, -p, --preserve-environment — Preserve the entire environment, i.e., do not set HOME, SHELL, USER or LOGNAME. The option is ignored if the option --login is specified. Sorry girl, --login wins that fight. 🙈
• -P, --pty — Create a pseudo-terminal for the session. The independent terminal provides better security as the user does not share a terminal with the original session. Please note security advice about TIOCSTI vulnerability below.

The entire session can also be moved to the background (e.g., runuser --pty -u user -- command &). If the pseudo-terminal is enabled, then runuser works as a proxy between the sessions (sync stdin and stdout).

This feature is mostly designed for interactive sessions. If the standard input is not a terminal, but for example a pipe (e.g., echo "date" | runuser --pty -u user), then the ECHO flag for the pseudo-terminal is disabled to avoid messy output.

• -s, --shell=shell — Run the specified shell instead of the default. The shell to run is selected according to the following rules, in order:
  • the shell specified with --shell
  • the shell specified in the environment variable SHELL if the --preserve-environment option is used
  • the shell listed in the passwd entry of the target user
  • /bin/sh

If the target user has a restricted shell (i.e., not listed in /etc/shells), then the --shell option and the SHELL environment variables are ignored unless the calling user is root.

• --session-command=command — Same as -c, but do not create a new session. (Discouraged.) Please note security advice about TIOCSTI vulnerability below. Girl... be careful. 😭
• -T, --no-pty — Do not create a pseudo-terminal, opposite of --pty and -P. Please note security advice about TIOCSTI vulnerability below.
• -u, --user=user — Run command with the effective user ID and group ID of the user name user.
• -w, --whitelist-environment=list — Don't reset the environment variables specified in the comma-separated list when clearing the environment for --login. The whitelist is ignored for the environment variables HOME, SHELL, USER, LOGNAME, and PATH. Those five are simply not up for negotiation, periodt. 💅
• -h, --help — Display help text and exit.
• -V, --version — Display version and exit.

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🌈 CONFIG FILES 🌈

runuser reads the /etc/default/runuser and /etc/login.defs configuration files. The following configuration items are relevant for runuser:

• ENV_PATH (string) — Defines the PATH environment variable for a regular user. The default value is /usr/local/bin:/bin:/usr/bin.
• ENV_ROOTPATH (string), ENV_SUPATH (string) — Defines the PATH environment variable for root. ENV_SUPATH takes precedence. The default value is /usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin.
• ALWAYS_SET_PATH (boolean) — If set to yes and --login and --preserve-environment were not specified runuser initializes PATH.

The environment variable PATH may be different on systems where /bin and /sbin are merged into /usr; this variable is also affected by the --login command-line option and the PAM system setting (e.g., pam_env(8)).

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⭐ EXIT STATUS ⭐

runuser normally returns the exit status of the command it executed. If the command was killed by a signal, runuser returns the number of the signal plus 128. Math girlie behavior 🧚

Exit status generated by runuser itself:

1. 1 — Generic error before executing the requested command
2. 126 — The requested command could not be executed
3. 127 — The requested command was not found

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🍓 FILES 🍓

• /etc/pam.d/runuser — default PAM configuration file
• /etc/pam.d/runuser-l — PAM configuration file if --login is specified
• /etc/default/runuser — runuser specific logindef config file
• /etc/login.defs — global logindef config file

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🔥 SECURITY NOTES 🔥

okay this is the important part, no skipping bestie. If runuser shares a terminal with the original session, it is potentially vulnerable to privilege escalation through TIOCSTI/TIOCLINUX ioctl command injection. 😭

There are two built-in ways to prevent this:

• Either you can use runuser with the -c option, which starts a new session via setsid(2) without a controlling terminal.
• Or, if your use case requires a controlling terminal, for example an interactive session, you can instruct runuser to use a pseudo terminal with the --pty or -P option.

Protect yourself, queen. Don't share terminals with strangers. 💅

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💜 HISTORY 💜

This runuser command was derived from coreutils' su, which was based on an implementation by David MacKenzie, and the Fedora runuser command by Dan Walsh. Glow-up lineage fr fr 👑

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🦋 SEE ALSO 🦋

setpriv(1), su(1), login.defs(5), shells(5), pam(8)

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🌸 REPORTING BUGS 🌸

For bug reports, use the issue tracker <https://github.com/util-linux/util-linux/issues>.

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✨ AVAILABILITY ✨

The runuser command is part of the util-linux package which can be downloaded from Linux Kernel Archive <https://www.kernel.org/pub/linux/utils/util-linux/>.

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and that's the whole page, bestie 🫶 this was util-linux 2.42.4, dated 2026-09-21, and it's the RUNUSER(1) manual — go run something with a substitute user and group ID, you've got this 💖✨🎀