setuid, setgid

Purpose

     Sets a process's user and group IDs.

Syntax

     int setuid (uid)                          int setgid (gid)
     int uid;                                  int gid;
     Description

     The setuid system  call sets the real  and effective user
     IDs of the calling process.   If the effective user ID of
     the  calling  process is  superuser,  then  the real  and
     effective user IDs are set to the value of the uid param-
     eter.  If the effective user ID of the calling process is
     not superuser, but the real user ID is equal to the value
     of the uid parameter, or the process's original effective
     user ID as  set by the exec system call  is equal to uid,
     then the effective user ID is set to the value of the uid
     parameter.

     The setgid system call sets  the real and effective group
     IDs of the calling process.   If the effective user ID of
     the  calling  process is  superuser,  then  the real  and
     effective  group IDs  are set  to  the value  of the  gid
     parameter.   If  the effective  user  ID  of the  calling
     process is not superuser, but  the real group ID is equal
     to the value of the  gid parameter, or the process's ori-
     ginal effective group  ID as set by the  exec system call
     is equal  to gid, then the  effective group ID is  set to
     the value of the gid parameter.

     Return Value

     Upon successful completion, a value of 0 is returned.  If
     the setuid or  setgid system call fails, then  a value of
     -1 is returned and errno is set to indicate the error.

     Diagnostics

     The setuid and setgid system  calls fail if the following
     is true:

     EPERM      The uid  (gid) parameter  is not equal  to the
                real user (group) ID of  the process or to the
                original effective  user (group) ID as  set by
                the exec  system call, and the  effective user
                ID is not superuser.

     EINVAL     The uid parameter is not a valid user ID.

     Related Information

     In  this book:   "exec:   execl,  execv, execle,  execve,
     execlp, execvp," "getpid, getpgrp, getppid," and "getuid,
     geteuid, getgid, getegid."