su

SU(1)                             User Commands                            SU(1)



NAME
       su - run a command with substitute user and group ID

SYNOPSIS
       su [options] [-] [user [argument...]]

DESCRIPTION
       su allows commands to be run with a substitute user and group ID.

       When called with no user specified, su defaults to running an interactive
       shell as root. When user is specified, additional arguments can be
       supplied, in which case they are passed to the shell.

       For backward compatibility, su defaults to not change the current
       directory and to only set the environment variables HOME and SHELL (plus
       USER and LOGNAME if the target user is not root). It is recommended to
       always use the --login option (instead of its shortcut -) to avoid side
       effects caused by mixing environments.

       This version of su uses PAM for authentication, account and session
       management. Some configuration options found in other su implementations,
       such as support for a wheel group, have to be configured via PAM.

       su is mostly designed for unprivileged users, the recommended solution
       for privileged users (e.g., scripts executed by root) is to use
       non-set-user-ID command runuser(1) that does not require authentication
       and provides separate PAM configuration. If the PAM session is not
       required at all then the recommended solution is to use command
       setpriv(1).

       Note that su 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 is modified by
       PAM.

OPTIONS
       -c, --command=command
           Pass command to the shell with the -c option.

       -f, --fast
           Pass -f to the shell, which may or may not be useful, depending on
           the shell.

       -g, --group=group
           Specify the primary group. This option is available to 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 TERM 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. This option is ignored if the option --login is
           specified.

       -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. This can be used to avoid TIOCSTI ioctl
           terminal injection and other security attacks against terminal file
           descriptors. The entire session can also be moved to the background
           (e.g., "su --pty - username -c application &"). If the
           pseudo-terminal is enabled, then su works as a proxy between the
           sessions (copy 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" | su --pty), 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), 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.)

       -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.

       -V, --version
           Display version information and exit.

       -h, --help
           Display help text and exit.

SIGNALS
       Upon receiving either SIGINT, SIGQUIT or SIGTERM, su terminates its child
       and afterwards terminates itself with the received signal. The child is
       terminated by SIGTERM, after unsuccessful attempt and 2 seconds of delay
       the child is killed by SIGKILL.

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

       FAIL_DELAY (number)
           Delay in seconds in case of an authentication failure. The number
           must be a non-negative integer.

       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 su 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)).

EXIT STATUS
       su normally returns the exit status of the command it executed. If the
       command was killed by a signal, su returns the number of the signal plus
       128.

       Exit status generated by su itself:

       1
           Generic error before executing the requested command

       126
           The requested command could not be executed

       127
           The requested command was not found

FILES
       /etc/pam.d/su
           default PAM configuration file

       /etc/pam.d/su-l
           PAM configuration file if --login is specified

       /etc/default/su
           command specific logindef config file

       /etc/login.defs
           global logindef config file

NOTES
       For security reasons, su always logs failed log-in attempts to the btmp
       file, but it does not write to the lastlog file at all. This solution can
       be used to control su behavior by PAM configuration. If you want to use
       the pam_lastlog(8) module to print warning message about failed log-in
       attempts then pam_lastlog(8) has to be configured to update the lastlog
       file as well. For example by:

          session required pam_lastlog.so nowtmp

HISTORY
       This su command was derived from coreutils' su, which was based on an
       implementation by David MacKenzie. The util-linux version has been
       refactored by Karel Zak.

SEE ALSO
       setpriv(1), login.defs(5), shells(5), pam(8), runuser(1)

REPORTING BUGS
       For bug reports, use the issue tracker at
       https://github.com/karelzak/util-linux/issues.

AVAILABILITY
       The su 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/>.



util-linux 2.37.2                  2021-06-02                              SU(1)