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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | SIGNALS | CONFIG FILES | EXIT STATUS | FILES | NOTES | HISTORY | SEE ALSO | AVAILABILITY | COLOPHON |
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SU(1) User Commands SU(1)
su - run a command with substitute user and group ID
su [options] [-] [user [argument...]]
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 provide separate PAM configuration. If the PAM
session is not required at all then the recommend solution is to
use command setpriv(1).
Note that su in all cases use 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.
-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:
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., 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:
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 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.
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.
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)).
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
/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 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
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.
setpriv(1), login.defs(5), shells(5), pam(8), runuser(1)
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/⟩.
This page is part of the util-linux (a random collection of Linux
utilities) project. Information about the project can be found
at ⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩. If you
have a bug report for this manual page, send it to
util-linux@vger.kernel.org. This page was obtained from the
project's upstream Git repository
⟨git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git⟩ on
2020-12-18. (At that time, the date of the most recent commit
that was found in the repository was 2020-12-17.) If you
discover any rendering problems in this HTML version of the page,
or you believe there is a better or more up-to-date source for
the page, or you have corrections or improvements to the
information in this COLOPHON (which is not part of the original
manual page), send a mail to man-pages@man7.org
util-linux July 2014 SU(1)
Pages that refer to this page: flock(1), homectl(1), login(1), login(1@@shadow-utils), machinectl(1), newgrp(1), runuser(1), setpriv(1), sg(1), updatedb(1), pam(3), pts(4), crontab(5), login.defs(5), passwd(5), passwd(5@@shadow-utils), shadow(5), suauth(5), credentials(7), PAM(8), pam_rootok(8), pam_xauth(8)
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