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SU(1)                       NetBSD Reference Manual                      SU(1)


NAME

     su - substitute user identity


SYNOPSIS

     su [-Kflm] [-c login-class] [login [shell arguments]]


DESCRIPTION

     su requests the Kerberos password for login (or for ``login.root'', if no
     login is provided), and switches to that user and group ID after obtain-
     ing a Kerberos ticket granting ticket.  A shell is then executed, and any
     additional shell arguments after the login name are passed to the shell.
     su will resort to the local password file to find the password for login
     if there is a Kerberos error.  If su is executed by root, no password is
     requested and a shell with the appropriate user ID is executed; no addi-
     tional Kerberos tickets are obtained.

     Alternatively, if the user enters the password "s/key", authentication
     will use the S/Key one-time password system as described in skey(1).
     S/Key is a Trademark of Bellcore.

     By default, the environment is unmodified with the exception of USER,
     HOME, SHELL, and SU_FROM.  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.  SU_FROM is set to
     the caller's login.  The invoked shell is the target login's.  With the
     exception of SU_FROM this is the traditional behavior of su.

     The options are as follows:

     -K      Do not attempt to use Kerberos to authenticate the user.

     -c      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.

     -l      Simulate a full login.  The environment is discarded except for
             HOME, SHELL, PATH, TERM, USER, and SU_FROM.  HOME SHELL, and
             SU_FROM are modified as above.  USER is set to the target login.
             PATH is set to is set to the path specified in the
             /etc/login.conf file (or to the default of
             ``/usr/bin:/bin:/usr/pkg/bin:/usr/local/bin'' ).  TERM is import-
             ed from your current environment.  The invoked shell is the tar-
             get login's, and su will change directory to the target login's
             home directory.

     -       Same as -l

     -m      Leave the environment unmodified.  The invoked shell is your lo-
             gin shell, and no directory changes are made.  As a security pre-
             caution, if the target user's shell is a non-standard shell (as
             defined by getusershell(3)) and the caller's real uid is non-ze-
             ro, 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), as listed in /etc/group,
     can su to ``root'', unless group wheel does not exist or has no members.
     (If you do not want anybody to be able to su to ``root'', make ``root''
     the only member of group ``wheel'', which is the default.)

     For sites with very large user populations, group ``wheel'' can contain
     the names of other groups that will be considered authorized to 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.


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).


EXAMPLES

     To become user username and use the same environment as in original
     shell, execute:

           su username

     To become user username and use environment as if full login would be
     performed, execute:

           su -l username

     To execute arbitrary command with privileges of user username, execute:

           su username -c "command args"


SEE ALSO

     csh(1), kinit(1), login(1), sh(1), skey(1), setusercontext(3), group(5),
     login.conf(5), passwd(5), environ(7), kerberos(8)


HISTORY

     A su command existed in Version 5 AT&T UNIX (and probably earlier).

NetBSD 1.6                       March 7, 2001                               2