SU(1)

NAME
su - Change user ID or become super-user

SYNOPSIS
su [OPTS] [-] [username [ARGS]]

DESCRIPTION
su is used to become another user during a login session. Invoked without a username, su defaults to becoming the super user. The optional argument - may be used to provide an environment similiar to what the user would expect had the user logged in directly.

The user will be prompted for a password, if appropriate. Invalid passwords will produce an error message. All attempts, both valid and invalid, are logged to detect abuses of the system.

An optional command can be executed. This is done by the shell specified in /etc/passwd for the target user unless the -s or -m options are used. Any arguments supplied after the username will be passed to the invoked shell (shell must support the -c command line option in order for a command to be passed to it).

Unless the -m or -p options are used, the current environment is passed to the new shell with alterations. The value of $PATH is reset to /bin:/usr/bin for normal users, or /sbin:/bin:/usr/sbin:/usr/bin for the super user. This may be changed with the ENV_PATH and ENV_SUPATH definitions in /etc/login.defs. $IFS, if is set, is reset to contain space, tab, and newline. $USER is set to the name of the target user, $HOME is set to the home directory of the target user, and $SHELL is set to the shell of the target user. When using the -m or -p options, the user's environment is not changed.

A subsystem login is indicated by the presense of a "*" as the first character of the login shell. The given home directory will be used as the root of a new filesystem which the user is actually logged into.

OPTIONS

-   make this a login shell

-c, --commmand=<command>
    pass command to the invoked shell using its -c option

-m, -p, --preserve-environment
    do not reset environment variables, and keep the same shell

-s, --shell=<shell>
    use shell instead of the default in /etc/passwd

NOTES
The -m, -p and -s options are restricted by the target user's shell being listed in /etc/shells. If it's not listed, then it's assumed to be a restricted account, a normal su is performed, and those options are ignored silently.

A subsystem login is indicated by the presense of a "*" as the first character of the login shell. The given home directory will be used as the root of a new filesystem which the user is actually logged into.

Much of the behavior of this command can be altered via its pam configuration - see pam(7)

CAVEATS

This version of su has many compilation options, only some of which may be in use at any particular site.

FILES
/etc/passwd - user account information
/etc/shadow - encrypted passwords and age information
/etc/shells - valid user shells
$HOME/.profile - initialization script for default shell

SEE ALSO
login(1), sh(1), login.defs(5), shells(5), pam(7)

AUTHOR
Julianne Frances Haugh (jfh@austin.ibm.com)