SU(1)                       General Commands Manual                      SU(1)


     su - substitute user identity


     su [-fKLlm] [-a auth-type] [-c login-class] [-s login-shell]
        [login [shell arguments]]


     The su utility allows a user to run a shell with the user and group ID of
     another user without having to log out and in as that other user.

     By default, the environment is unmodified with the exception of LOGNAME,
     HOME, SHELL, and USER.  HOME and SHELL are set to the target login's
     default values.  LOGNAME and USER are set to the target login, unless the
     target login has a user ID of 0 and the -l flag was not specified, in
     which case it is unmodified.  The invoked shell is the target login's.
     This is the traditional behavior of su.

     If not using -m and the target login has a user ID of 0 then the PATH
     variable and umask value (see umask(2)) are always set according to the
     /etc/login.conf file (see login.conf(5)).

     The options are as follows:

     -       Same as the -l option (deprecated).

     -a auth-type
             Specify an authentication type such as ``skey'' or ``radius''.

     -c login-class
             Specify a login class.  You may only override the default class
             if you're already root.

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

     -K      This is shorthand for ``su -a passwd'', provided for backwards

     -L      Loop until a correct username and password combination is
             entered, similar to login(1).  Note that in this mode target
             login must be specified explicitly, either on the command line or
             interactively.  Additionally, su will prompt for the password
             even when invoked by root.

     -l      Simulate a full login.  The environment is discarded except for
             HOME, SHELL, PATH, TERM, LOGNAME, and USER.  HOME and SHELL are
             modified as above.  LOGNAME and USER are set to the target login.
             PATH is set to the value specified by the ``path'' entry in
             login.conf(5).  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.

     -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.

     -s login-shell
             Specify the path to an alternate login shell.  You may only
             override the shell if you're already root.  This option will
             override the shell even if the -m option is specified.

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

     If the optional shell arguments are provided on the command line, they
     are passed to the login shell of the target login.  This allows it to
     pass arbitrary commands via the -c option as understood by most shells.
     Note that -c usually expects a single argument only; you have to quote it
     when passing multiple words.

     If group 0 (normally ``wheel'') has users listed then only those users
     can su to ``root''.  It is not sufficient to change a user's /etc/passwd
     entry to add them to the ``wheel'' group; they must explicitly be listed
     in /etc/group.  If no one is in the ``wheel'' group, it is ignored, and
     anyone who knows the root password is permitted to su to ``root''.

     By default (unless the prompt is reset by a startup file) the superuser
     prompt is set to ``#'' to remind one of its awesome power.


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

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

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

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

     USER     Same as LOGNAME.


     Run the command ``makewhatis'' as user ``bin''.  You will be asked for
     bin's password unless your real UID is 0.

           $ su bin -c makewhatis

     Same as above, but the target command consists of more than a single

           $ su bin -c 'makewhatis /usr/local/man'

     Same as above, but the target command is run with the resource limits of
     the login class ``staff''.  Note that the first -c option applies to su
     while the second is an argument to the shell.

           $ su -c staff bin -c 'makewhatis /usr/local/man'

     Pretend a login for user ``foo'':

           $ su -l foo

     Same as above, but use S/Key for authentication:

           $ su -a skey -l foo


     doas(1), login(1), setusercontext(3), group(5), login.conf(5), passwd(5),


     A su command appeared in Version 7 AT&T UNIX.


     The login name is not optional for root if there are shell arguments.

OpenBSD 5.9                      July 30, 2015                     OpenBSD 5.9

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