setuid(2)                                                         setuid(2)


   NAME
         setuid, setgid - set user and group IDs

   SYNOPSIS
         #include <sys/types.h>
         #include <unistd.h>

         int setuid(uid_t uid);

         int setgid(gid_t gid);

   DESCRIPTION
         The setuid system call sets the real user ID, effective user ID, and
         saved user ID of the calling process.  The setgid system call sets
         the real group ID, effective group ID, and saved group ID of the
         calling process.

         At login time, the real user ID, effective user ID, and saved user ID
         of the login process are set to the login ID of the user responsible
         for the creation of the process.  The same is true for the real,
         effective, and saved group IDs; they are set to the group ID of the
         user responsible for the creation of the process.

         When a process calls exec(2) to execute a file (program), the user
         and/or group identifiers associated with the process can change.  If
         the file executed is a set-user-ID file, the effective and saved user
         IDs of the process are set to the owner of the file executed.  If the
         file executed is a set-group-ID file, the effective and saved group
         IDs of the process are set to the group of the file executed.  If the
         file executed is not a set-user-ID or set-group-ID file, the
         effective user ID, saved user ID, effective group ID, and saved group
         ID are not changed.

         The following subsections describe the behavior of setuid and setgid
         with respect to the three types of user and group IDs.

      setuid
         If the effective user ID of the process calling setuid is the
         superuser, the real, effective, and saved user IDs are set to the uid
         parameter.

         If the effective user ID of the calling process is not the superuser,
         but uid is either the real user ID or the saved user ID of the
         calling process, the effective user ID is set to uid.

      setgid
         If the effective user ID of the process calling setgid is the
         superuser, the real, effective, and saved group IDs are set to the
         gid parameter.




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   setuid(2)                                                         setuid(2)


         If the effective user ID of the calling process is not the superuser,
         but gid is either the real group ID or the saved group ID of the
         calling process, the effective group ID is set to gid.

         setuid and setgid fail if one or more of the following is true:

         EPERM     For setuid, if the effective user ID is not the superuser,
                   and the uid parameter does not match either the real or
                   saved user IDs.  For setgid, if the effective user ID is
                   not the superuser, and the gid parameter does not match
                   either the real or saved group IDs.

         EINVAL    The uid or gid is out of range.

   DIAGNOSTICS
         Upon successful completion, a value of 0 is returned.  Otherwise, a
         value of -1 is returned and errno is set to indicate the error.

   SEE ALSO
         intro(2), exec(2), getgroups(2), getuid(2), stat(5).

































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