.\" Copyright (c) 1996 Charles M. Hannum.  All rights reserved.
.\" Copyright (c) 1980, 1991 The Regents of the University of California.
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.\"     from: @(#)setreuid.2	6.4 (Berkeley) 3/10/91
.\"	$Id: setreuid.2,v 1.6 1996/06/23 11:52:56 mycroft Exp $
.\"
.Dd June 23, 1996
.Dt SETREUID 2
.Os BSD 4.2
.Sh NAME
.Nm setreuid
.Nd set real and effective user ID's
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft int
.Fn setreuid "int ruid" "int euid"
.Sh DESCRIPTION
The real and effective user ID's of the
current process are set according to the arguments.  If the real user ID
is changed, the saved user ID is changed to the new value of the effective
user ID.
.Pp
If
.Fa ruid
or 
.Fa euid
is -1, the current uid is filled in by the system.
Unprivileged users may change the real user
ID to the effective user ID, and may change the effective user ID to the
real user ID or the saved user ID; only the super-user may
make other changes.
.Pp
The
.Fn setreuid
function has been used to swap the real and effective user
IDs in set-user-ID programs to temporarily relinquish the set-user-ID
value.  This purpose is now better served by the use of the
.Fn seteuid
function (see
.Xr setuid 2 ).
.Pp
When setting the real and effective user IDs to the same value, this
function is equivalent to the
.Fn setuid
function.
When setting only the effective user ID, this function is equivalent to
the
.Fn seteuid
function.
.Sh RETURN VALUES
Upon successful completion, a value of 0 is returned.  Otherwise,
a value of -1 is returned and
.Va errno
is set to indicate the error.
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er EPERM
The current process is not the super-user and a change
other than changing the effective user-id to the real user-id
was specified.
.El
.Sh SEE ALSO
.Xr getuid 2 ,
.Xr seteuid 2 ,
.Xr setuid 2 ,
.Xr setgid 2
.Sh HISTORY
The
.Fn setreuid
function call appeared in
.Bx 4.2
and was dropped in
.Bx 4.4 .
It was reimplemented in
.Nx 1.2
in a way compatible with
.Bx 4.3 ,
SunOS and Linux.