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.\"     from: @(#)setuid.3	6.4 (Berkeley) 4/19/91
.\"	$Id: setuid.2,v 1.2 1994/04/10 00:16:58 cgd Exp $
.\"
.Dd April 19, 1991
.Dt SETUID 2
.Os BSD 4.2
.Sh NAME
.Nm setuid ,
.Nm seteuid ,
.Nm setgid ,
.Nm setegid
.Nd set user and group ID
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <unistd.h>
.Ft int
.Fn setuid "uid_t uid"
.Ft int
.Fn seteuid "uid_t euid"
.Ft int
.Fn setgid "gid_t gid"
.Ft int
.Fn setegid "gid_t egid"
.Sh DESCRIPTION
The
.Fn setuid
function sets the real and effective user IDs and the saved
set-user-ID of the current process to the specified value.  The
.Fn setuid
function is permitted if the specified ID is equal to the real user ID of
the process, or if the effective user ID is that of the super user.
.Pp
The
.Fn setgid
function sets the real and effective group IDs and the saved
set-group-ID of the current process to the specified value.  The
.Fn setgid
function is permitted if the specified ID is equal to the real group ID
of the process, or if the effective user ID is that of the super user.
.Pp
The
.Fn seteuid
function sets the effective user ID
of the current process.  The effective user ID may be set to the value of
the real user ID or the saved set-user-ID (see
.Xr intro 2 
and
.Xr execve 2 );
in this way, the effective user ID of a set-user-ID executable may be
toggled by switching to the real user ID, then re-enabled by reverting to
the set-user-ID value.
Similarly, with 
.Fn setegid
the effective group ID may be set to
the value of the real group ID or the saved set-user-ID.
.Sh RETURN VALUES
Upon success, these functions return 0;
otherwise \-1 is returned.
.Pp
If the user is not the super user, or the uid (gid) specified is not
the real ID, effective ID, or saved ID of the process,
these functions return \-1.
.Sh SEE ALSO
.Xr getuid 2 ,
.Xr getgid 2
.Sh HISTORY
The
.Fn setuid
and
.Fn setgid
functions are compliant with the
.St -p1003.1-88
specification with
.Li _POSIX_SAVED_IDS
not defined.
The
.Fn seteuid
and
.Fn setegid
functions are extensions based on the 
.Tn POSIX
concept of
.Li _POSIX_SAVED_IDS ,
and have been proposed for a future revision of the standard.