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SU(1)                     BSD General Commands Manual                    SU(1)

NAME
     su -- substitute user identity

SYNOPSIS
     su [-] [-flm] [login [args]]

DESCRIPTION
     The su utility requests appropriate user credentials via PAM and switches to that user ID (the default
     user is the superuser).  A shell is then executed.

     PAM is used to set the policy su(1) will use.  In particular, by default only users in the ``admin'' or
     ``wheel'' groups can switch to UID 0 (``root'').  This group requirement may be changed by modifying
     the ``pam_group'' section of /etc/pam.d/su.  See pam_group(8) for details on how to modify this set-ting. setting.
     ting.

     By default, the environment is unmodified with the exception of USER, HOME, and SHELL.  HOME and SHELL
     are set to the target login's default values.  USER is set to the target login, unless the target login
     has a user ID of 0, in which case it is unmodified.  The invoked shell is the one belonging to the tar-get target
     get login.  This is the traditional behavior of su.

     The options are as follows:

     -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.

     -       (no letter) The same as -l.

     -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 (or -) and -m options are mutually exclusive; the last one specified overrides any previous
     ones.

     If the optional args are provided on the command line, they are passed to the login shell of the target
     login.  Note that all command line arguments before the target login name are processed by su itself,
     everything after the target login name gets passed to the login shell.

     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.

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).

FILES
     /etc/pam.d/su  PAM configuration for su.

EXAMPLES
     su man -c catman
            Runs the command catman as user man.  You will be asked for man's password unless your real UID
            is 0.
     su man -c 'catman /usr/share/man /usr/local/man'
            Same as above, but the target command consists of more than a single word and hence is quoted
            for use with the -c option being passed to the shell.  (Most shells expect the argument to -c to
            be a single word).
     su -l foo
            Simulate a login for user foo.
     su - foo
            Same as above.
     su -   Simulate a login for root.

SEE ALSO
     csh(1), sh(1), group(5), passwd(5), environ(7), pam_group(8)

HISTORY
     A su command appeared in Version 1 AT&T UNIX.

BSD                           September 13, 2006                           BSD

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