SU(1)

NAME
su - substitute user identity

SYNOPSIS
su [-flm] [login] [-c shell arguments]

DESCRIPTION
su requests the password for login and switches to that user and group ID after obtaining proper authentication. A shell is then executed, and any additional shell arguments after the login name are passed to the shell. If su is executed by root, no password is requested and a shell with the appropriate user ID is executed.

The options are as follows:

-c  Invoke the following command in a subshell as the specified user.

-f  If the invoked shell is csh(1), this option prevents it from reading the “.cshrc” file.

-l  Simulate a full login. The environment is discarded except for HOME, SHELL, PATH, TERM, and USER. HOME and SHELL are modified as above. USER is set to the target login. PATH is set to “/bin:/usr/bin”. TERM is imported from your current environment. The invoked shell is the target login's, and su will change directory to the target login's home directory. This option is identical to just passing "-", as in "su -".

-m  Leave the environment unmodified. The invoked shell is your login shell, and no directory changes are made. As a security precaution, if the target user's shell is a non-standard shell (as defined by getusershell(3)) and the caller's real uid is non-zero, su will fail.

The -l and -m options are mutually exclusive; the last one specified overrides any previous ones.

Only users in group “wheel” (normally gid 0) or group “admin” (normally gid 20) can su to “root”.

By default (unless the prompt is reset by a startup file) the super-user prompt is set to “#” to remind one of its awesome power.

SEE ALSO
csh(1), login(1), sh(1), skey(1), kinit(1), kerberos(1), passwd(5), group(5), environ(7)

ENVIRONMENT
Environment variables used by su :

HOME
    Default home directory of real user ID unless modified as specified above.

PATH
    Default search path of real user ID unless modified as specified above.

TERM
    Provides terminal type which may be retained for the substituted user ID.

USER
    The user ID is always the effective ID (the target user ID) after an su unless the user ID is 0 (root).

HISTORY
A su command appeared in AT&T UNIX.