SU(1)                   NetBSD General Commands Manual                   SU(1)

NAME
     su -- substitute user identity

SYNOPSIS
     su [-dfKlm] [-c login-class] [login[:group] [shell arguments]]
     su [-dfKlm] [-c login-class] [:group [shell arguments]]

DESCRIPTION
     su allows one user to become another user login without logging out and
     in as the new user.  If a group is specified and login is a member of
     group, then the group is changed to group rather than to login's primary
     group.  If login is omitted and group is provided (form two above), then
     login is assumed to be the current username.

     When executed by a user, the login user's password is requested.  When
     using Kerberos, the password for login (or for ``login.root'', if no
     login is provided) is requested, and su switches to that user and group
     ID after obtaining 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 additional 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 LOGNAME,
     USER, HOME, SHELL, and SU_FROM.  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, in which case they are unmod-
     ified.  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:

     -c      Specify a login class.  You may only override the default class
             if you're already root.  See login.conf(5) for details.

     -d      Same as -l, but does not change the current directory.

     -f      If the invoked shell is csh(1), this option prevents it from
             reading the ``.cshrc'' file.  If the invoked shell is sh(1), or
             ksh(1), this option unsets ENV, thus preventing the shell from
             executing the startup file pointed to by this variable.

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

     -l      Simulate a full login.  The environment is discarded except for
             HOME, SHELL, PATH, TERM, LOGNAME, USER, and SU_FROM.  HOME,
             SHELL, and SU_FROM are modified as above.  LOGNAME and USER are
             set to the target login.  PATH 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
             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.  The utmp(5), wtmp(5), and lastlogin(5)
             databases are not updated.

     -       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 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.

CUSTOMIZATION
     Changing required group
       For the pam(8) version of su the name of the required group can be
       changed by setting gname in pam.conf(5):

       auth requisite pam_group.so no_warn group=gname root_only fail_safe

       For the non pam(8) version of su the same can be achieved by compiling
       with SU_GROUP set to the desired group name.

     Supplying own password
       su can be configured so that users in a particular group can supply
       their own password to become ``root''.  For the pam(8) version of su
       this can be done by adding a line to pam.conf(5) such as:

       auth sufficient pam_group.so no_warn group=gname root_only authenticate

       where gname is the name of the desired group.  For the non pam(8) ver-
       sion of su the same can be achieved by compiling with SU_ROOTAUTH set
       to the desired group name.

     Indirect groups
       This option is not available with the pam(8) version of su.  For the
       non pam(8) version of su, if SU_INDIRECT_GROUP is defined, the SU_GROUP
       and SU_ROOTAUTH groups are treated as indirect groups.  The group mem-
       bers of those two groups are treated as groups themselves.

ENVIRONMENT
     Environment variables used by su:

     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
           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).

EXIT STATUS
     su returns the exit status of the executed subshell, or 1 if any error
     occurred while switching privileges.

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

     When a -c option is included after the login name it is not a su option,
     because any arguments after the login are passed to the shell.  (See
     csh(1), ksh(1) or sh(1) for details.)  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 7.0                     November 20, 2012                    NetBSD 7.0

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