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 to run commands with a substitute user and group ID.

       When called without arguments, su defaults to running an interactive
       shell as root.

       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
       provide separate PAM configuration. If the PAM session is not required
       at all then the recommend solution is to use command setpriv(1).


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 supplemental 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 unspecified.

       -, -l, --login
              Start the shell as a login shell with an environment similar to
              a real login:

                 o      clears all the environment variables except TERM and
                        variables specified by --whitelist-environment

                 o      initializes the environment variables HOME, SHELL,
                        USER, LOGNAME, and PATH

                 o      changes to the target user's home directory

                 o      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. it does not set HOME,
              SHELL, USER nor LOGNAME.  This option is ignored if the option
              --login is specified.

       -P, --pty
              Create pseudo-terminal for the session. The independent terminal
              provides better security as user does not share terminal with
              the original session.  This allow to avoid TIOCSTI ioctl
              terminal injection and another security attacks against terminal
              file descriptors. The all session is also possible to move to
              background (e.g. "su --pty - username -c application &"). If the
              pseudo-terminal is enabled then su command 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 pipe (e.g.
              echo "date" | su --pty) than 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:

                 o      the shell specified with --shell

                 o      the shell specified in the environment variable SHELL,
                        if the --preserve-environment option is used

                 o      the shell listed in the passwd entry of the target
                        user

                 o      /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 environment variables specified in comma separated
              list when clears 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(1):

       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.

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
       allows to control su behavior by PAM configuration.  If you want to use
       the pam_lastlog module to print warning message about failed log-in
       attempts then the pam_lastlog has to be configured to update the
       lastlog file as well. For example by:

              session  required  pam_lastlog.so nowtmp

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

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

AVAILABILITY
       The su command is part of the util-linux package and is available from
       Linux Kernel Archive ⟨https://www.kernel.org/pub/linux/utils/util-
       linux/⟩.



util-linux                         July 2014                             SU(1)