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NetBSD 6.1.5 - man page for su (netbsd section 1)

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

     su -- substitute user identity

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

     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 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:

     -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 pre-
	     venting 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.

     -	     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

     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.

     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) version 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 members of those two groups are treated as groups themselves.

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

     Environment variables used by su:

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

	   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).

     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 argu-
     ments 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"

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

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

BSD					 October 27, 2007				      BSD

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