SU(1) User Commands SU(1)
su - run a command with substitute user and group ID
su [options...] [-] [user [args...]]
su allows to run commands with 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 it's shortcut -) to
avoid side effects caused by mixing environments.
This version of su uses PAM for authentication, account and session management. Some con-
figuration options found in other su implementations such as e.g. support of a wheel group
have to be configured via PAM.
-c command, --command=command
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 allowed for root user only
specify a supplemental group, this option is allowed for root user only
-, -l, --login
Starts the shell as login shell with an environment similar to a real login:
o clears all environment variables except for TERM
o initializes the environment variables HOME, SHELL, USER, LOGNAME, 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, ie does not set HOME, SHELL, USER nor LOGNAME.
The option is ignored if the option --login is specified.
-s SHELL, --shell=SHELL
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 user
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.
--help Display help text and exit.
Display version information and exit.
su reads the /etc/default/su and /etc/login.defs configuration files. The following con-
figuration items are relevant for su(1):
Delay in seconds in case of authentication failure. Number must be a non-negative
Defines the PATH environment variable for a regular user. The default value is
Defines the PATH environment variable for root. The default value is /usr/local/sbin:
If set to yes and --login and --preserve-environment were not specified su initializes
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 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
runuser(8), pam(8), shells(5), login.defs(5)
Derived from coreutils' su which was based on an implementation from David MacKenzie.
The su command is part of the util-linux package and is available from Linux Kernel
util-linux June 2012 SU(1)