su.md

su

switch user

run a command with substitute user and group ID

---

References

• man su

Synopsis

su [options...] [-] [user [args...]]

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

Options

• -c command, --command=command Pass command to the shell.
• --session-command=command Same as -c but do not create a new session (discouraged).
• -g, --group=group Specify the primary group, this option is allowed for 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 Starts the shell as login shell with an environment similar to a real login:
  • clears all environment variables except for TERM
  • initializes the environment variables HOME, SHELL, USER, LOGNAME, 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 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:
    • 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.

Usage

Default

su
# same as
su root