setuid(2)                        UNIX System V                        setuid(2)


NAME
      setuid, setgid - set user and group IDs

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

      int setuid(uidt uid);

      int setgid(gidt 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.

      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.




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setuid(2)                        UNIX System V                        setuid(2)


      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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