SU(1) User Commands SU(1)NAMEsu - run a command with substitute user and group ID
SYNOPSISsu [options] [-] [user [argument...]]
DESCRIPTIONsu 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 direc‐
tory 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 implementa‐
tions, such as support of a wheel group, have to be configured via PAM.
Pass command to the shell with the -c option.
Same as -c but do not create a new session (discouraged).
Pass -f to the shell, which may or may not be useful, depending
on the shell.
Specify the primary group. This option is available for the
root user only.
Specify a supplemental group. This option is available for the
root user only.
-, -l, --login
Starts the shell as login shell with an environment similar to a
o clears all environment variables except TERM
o initializes the environment variables HOME, SHELL,
USER, LOGNAME, and PATH
o changes to the target user's home directory
o sets argv of the shell to '-' in order to make the
shell a login shell
-m, -p, --preserve-environment
Preserves the whole environment, i.e. it does not set HOME,
SHELL, USER nor LOGNAME. This option is ignored if the option
--login is specified.
Runs 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
If the target user has a restricted shell (i.e. not listed in
/etc/shells), the --shell option and the SHELL environment vari‐
ables are ignored unless the calling user is root.
--help Display help text and exit.
Display version information and exit.
Upon receiving either SIGINT, SIGQUIT or SIGTERM, su terminates its
child and afterwards terminates itself with the received signal.
CONFIG FILESsu reads the /etc/default/su and /etc/login.defs configuration files.
The following configuration items are relevant for su(1):
Delay in seconds in case of authentication failure. Number must be
a non-negative integer.
Defines the PATH environment variable for a regular user. The
default value is /usr/local/bin:/bin:/usr/bin.
Defines the PATH environment variable for root. The default value
If set to yes and --login and --preserve-environment were not spec‐
ified su initializes PATH.
EXIT STATUSsu 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
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 could was not found
/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
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 lastlog
file too. For example by:
session required pam_lastlog.so nowtmp
SEE ALSOrunuser(8), pam(8), shells(5), login.defs(5)AUTHOR
Derived from coreutils' su which was based on an implementation from
The su command is part of the util-linux package and is available from
Linux Kernel Archive ⟨ftp://ftp.kernel.org/pub/linux/utils/util-
util-linux October 2013 SU(1)