run0

systemd

run0

Elevate privileges

run0

OPTIONS

COMMAND

Description

run0 may be used to temporarily and interactively acquire elevated or different privileges. It serves a similar purpose as sudo(8), but operates differently in a couple of key areas:

No execution or security context credentials are inherited from the caller into the invoked commands, as they are invoked from a fresh, isolated service forked off by the service manager.
Authentication takes place via polkit, thus isolating the authentication prompt from the terminal (if possible).
An independent pseudo-tty is allocated for the invoked command, detaching its lifecycle and isolating it for security.
No SetUID/SetGID file access bit functionality is used for the implementation.

Altogether this should provide a safer and more robust alternative to the sudo mechanism, in particular in OS environments where SetUID/SetGID support is not available (for example by setting the NoNewPrivileges= variable in systemd-system.conf(5)).

Any session invoked via run0 will run through the systemd-run0 PAM stack, except for interactive shells started via systemd-ptybrokerd.service(8), which run through the systemd-ptybroker-shell PAM stack instead.

Note that run0 is implemented as an alternative multi-call invocation of systemd-run(1). That is, run0 is a symbolic link to systemd-run executable file, and it behaves as run0 if it is invoked through the symbolic link, otherwise behaves as systemd-run.

Note that TTY isolation as provided by the default value of the --pty option is a core feature of run0. Redirecting terminals must therefore be done with care, avoiding giving such control to untrusted programs.

When run0 is invoked locally on a terminal to run an interactive shell (i.e. without an explicit command), and no options are specified that require the transient service unit to be set up in a specific way (such as --unit=, --property= or --slice=), the session is not created via the service manager APIs directly. Instead, the pseudo TTY and the shell running on it are requested from systemd-ptybrokerd.service(8), which allocates the pseudo TTY, retains its frontend (i.e. master) side and invokes the shell as a transient service unit on its backend. In this mode privileges are authorized via the io.systemd.PTYBroker.acquire-pty-with-shell polkit action (rather than the org.freedesktop.systemd1.manage-units action used otherwise), the pseudo TTY of the session remains registered with the broker for the lifetime of the session (and may be listed, monitored or hung up via ptyctl(1)).

Options

The following options are understood:

--unit=
Use this unit name instead of an automatically generated one.

--property=
Sets a property of the service unit that is created. This option takes an assignment in the same format as systemctl(1)'s set-property command.

--description=
Provide a description for the service unit that is invoked. If not specified, the command itself will be used as a description. See Description= in systemd.unit(5).

--slice=
Make the new .service unit part of the specified slice, instead of user.slice. This option conflicts with --lightweight= and --area=, and implies XDG_SESSION_CLASS=none, to keep the new process within the specified slice instead of a new session scope.

--slice-inherit
Make the new .service unit part of the slice the run0 itself has been invoked in. This option may be combined with --slice=, in which case the slice specified via --slice= is placed within the slice the run0 command is invoked in. Also conflicts with --lightweight= and --area= and implies XDG_SESSION_CLASS=none, similar to --slice=.

Example: consider run0 being invoked in the slice foo.slice, and the --slice= argument is bar. The unit will then be placed under foo-bar.slice.

--user=; -u; --group=; -g
Switches to the specified user/group. If not specified defaults to root, unless --area= or --empower are used (see below), in which case this defaults to the invoking user.

--nice=
Runs the invoked session with the specified nice level.

--chdir=; -D
Runs the invoked session with the specified working directory. If not specified defaults to the client's current working directory if switching to the root user, or the target user's home directory otherwise.

-k; --reset-timestamp
Revokes temporary polkit authorization for this terminal, if present.

-K; --remove-timestamp
Revokes all temporary polkit authorizations for this user session.

-v; --validate
Request authorization from polkit. Can be used to create a temporary authorization without running a command.

--via-shell
Invokes the target user's login shell and runs the specified command (if any) via it.

-i
Shortcut for --via-shell --chdir='~'.

--setenv=NAME[=VALUE]
Runs the invoked session with the specified environment variable set. This parameter may be used more than once to set multiple variables. When = and <VALUE> are omitted, the value of the variable with the same name in the invoking environment will be used.

--background=COLOR
Change the terminal background color to the specified ANSI color as long as the session lasts. If not specified, the background will be tinted in a reddish tone when operating as root, and in a yellowish tone when operating under another UID, as reminder of the changed privileges. The color specified should be an ANSI X3.64 SGR background color, i.e. strings such as 40, 41, …, 47, 48;2;…, 48;5;…. See ANSI Escape Code (Wikipedia) for details. Set to an empty string to disable.

Example: --background=44 for a blue background.

--pty; --pty-late; --pipe
Request allocation of a pseudo TTY for the run0 session (in case of --pty or --pty-late), or request passing the caller's STDIO file descriptors directly through (in case of --pipe). --pty-late is very similar to --pty but begins the TTY processing only once unit startup is complete, leaving input to any passwords/polkit agents until that time. If neither switch is specified, or if both --pipe and one of --pty/--pty-late are specified, the mode will be picked automatically: if standard input, standard output, and standard error output are all connected to a TTY then a pseudo TTY is allocated (in --pty-late mode unless --no-ask-password is specified in which case --pty is selected), otherwise the relevant file descriptors are passed through directly.

As mentioned above, TTY isolation as implemented by the default value of this option is crucial for security, so care must be taken when overriding it.

--pty and --pipe were added in v257.

--pty-late was added in v258.

--shell-prompt-prefix=STRING
Set a shell prompt prefix string. This ultimately controls the $SHELL_PROMPT_PREFIX environment variable for the invoked program, which is typically imported into the shell prompt. By default – if emojis are supported –, a superhero emoji is shown (🦸). This default may also be changed (or turned off) by passing the $SYSTEMD_RUN_SHELL_PROMPT_PREFIX environment variable to run0, see below. Set to an empty string to disable shell prompt prefixing.

--lightweight=BOOLEAN
Controls whether to activate the per-user service manager for the target user. By default (unset or set to auto), if the target user is root or a system user the per-user service manager is not activated as effect of the run0 invocation, otherwise it is.

This ultimately controls the $XDG_SESSION_CLASS environment variable pam_systemd(8) respects.

--area=AREA
Controls the "area" of the target account to log into. Areas are secondary home directories within the primary home directory of the target user, i.e. logging into area foobar of an account translates to $HOME being set to ~/Areas/foobar on login.

If this option is used, the default user to transition to changes from root to the calling user's (but --user= takes precedence, see above). Or in other words, just specifying an area without a user is a mechanism to create a new session of the calling user, just with a different area.

This ultimately controls the $XDG_AREA environment variable pam_systemd(8) respects.

For details on the area concept see pam_systemd_home(8).

--empower
If specified, run0 will elevate the privileges of the selected user (using --user=) or the current user if no user is explicitly selected. Currently this means we give the invoked process all available capabilities and add the empower group as a supplemental group (for which all polkit actions are allowed by default), but other privileges may be granted in the future as well when using this option.

Note that other (unprivileged) processes of the selected user will have privileges over the invoked process. Consider not using this option in an environment where there might be malicious processes running as the selected user.

--same-root-dir
Execute the run0 session in the same root directory that the run0 command is executed in.

--machine=
Execute operation in a local container. Specify a container name to connect to.

-n; --non-interactive
Equivalent to --no-ask-password.

--no-pager
Do not pipe output into a pager. This currently only applies to --help. (The pager is not started during normal operation.)

All command line arguments after the first non-option argument become part of the command line of the launched process. If no command line is specified an interactive shell is invoked. The shell to invoke may be controlled through --via-shell - when specified the target user's shell is used - or --setenv=SHELL=…. By default, the originating user's shell is executed if operating locally, or /bin/sh when operating with --machine=.

Note that unlike sudo, run0 always spawns shells with login shell semantics, regardless of -i.

Exit status

On success, 0 is returned. If run0 failed to start the session or the specified command fails, a non-zero return value will be returned.

Environment Variables

As with systemd-run, the session will inherit the system environment from the service manager. In addition, the following environment variables will be set:

$TERM
Copied from the $TERM of the caller. Can be overridden with --setenv=

$SUDO_USER
Set to the username of the originating user.

$SUDO_UID
Set to the numeric UNIX user id of the originating user.

$SUDO_GID
Set to the primary numeric UNIX group id of the originating session.

$SHELL_PROMPT_PREFIX
By default, set to the superhero emoji (if supported), but may be overridden with the $SYSTEMD_RUN_SHELL_PROMPT_PREFIX environment variable (see below), or the --shell-prompt-prefix= switch (see above).

The following variables may be passed to run0:

$SYSTEMD_RUN_SHELL_PROMPT_PREFIX
If set, overrides the default shell prompt prefix that run0 sets for the invoked shell (the superhero emoji). Set to an empty string to disable shell prompt prefixing.