SU(1L)

NAME
su - run a shell with substitute user and group IDs

SYNOPSIS
su [-flmp] [-c command] [-s shell] [--login] [--fast] [--preserve-environment] [--command=command] [--shell=shell] [-] [user [arg...]]

DESCRIPTION
This manual page documents the GNU version of su. su allows one user to temporarily become another user. It runs a shell with the real and effective user ID, group ID, and supplemental groups of USER. If no USER is given, the default is root, the super-user. The shell run is taken from USER's password entry, or /bin/sh if none is specified there. If USER has a password, su prompts for the password unless run by a user with real user ID 0 (the super-user).

By default, su does not change the current directory. It sets the environment variables `HOME' and `SHELL' from the password entry for USER, and if USER is not the super-user, sets `USER' and `LOGNAME' to USER. By default, the shell is not a login shell.

If one or more ARGs are given, they are passed as additional arguments to the shell.

su does not handle /bin/sh or other shells specially (setting argv[0] to "-su", passing -c only to certain shells, etc.).

On systems that have syslog, su can be compiled to report failed, and optionally successful, su attempts using syslog.

This program does not support a "wheel group" that restricts who can su to super-user accounts, because that can help fascist system administrators hold unwarranted power over other users.

  OPTIONS

-, -l, --login
    Make the shell a login shell. This means the following. Unset all environment variables except `TERM', `HOME', and `SHELL' (which are set as described above), and `USER' and `LOGNAME' (which are set, even for the super-user, as described above), and set `PATH' to a compiled-in default value. Change to USER's home directory. Prepend "-" to the shell's name, to make it read its login startup file(s).

-c COMMAND, --commmand=COMMAND
    Pass COMMAND, a single command line to run, to the shell with a -c option instead of starting an interactive shell.

-f, --fast
    Pass the -f option to the shell. This probably only makes sense with csh and tcsh, for which the -f option prevents reading the startup file (.cshrc). With Bourne-like shells, the -f option disables filename pattern expansion, which is not a generally desirable thing to do.

-m, -p, --preserve-environment
    Do not change the environment variables `HOME', `USER', `LOGNAME', or `SHELL'. Run the shell given in the environment variable `SHELL' instead of USER's shell from /etc/passwd, unless the user running su is not the superuser and USER's shell is restricted. A restricted shell is one that is not listed in the file /etc/shells, or in a compiled-in list if that file does not exist. Parts of what this option does can be overridden by --login and --shell.

-s, --shell shell
    Run SHELL instead of USER's shell from /etc/passwd, unless the user running su is not the superuser and USER's shell is restricted.

The long-named options can be introduced with `+' as well as `--', for compatibility with previous releases. Eventually support for `+' will be removed, because it is incompatible with the POSIX.2 standard.