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.\"	$OpenBSD: setreuid.3,v 1.8 2000/04/18 02:31:32 aaron Exp $
.\"
.Dd March 10, 1991
.Dt SETREUID 3
.Os
.Sh NAME
.Nm setreuid
.Nd set real and effective user IDs
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft int
.Fn setreuid "int ruid" "int euid"
.Sh DESCRIPTION
The real and effective user IDs of the
current process are set according to the arguments.
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 vice-versa; only the superuser 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, the standard
.Fn setuid
function is preferred.
.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 superuser 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
.Sh HISTORY
The
.Fn setreuid
function call appeared in
.Bx 4.2
and was dropped in
.Bx 4.4 .