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.\"     @(#)setreuid.2	8.2 (Berkeley) 4/16/94
.\"
.Dd April 16, 1994
.Dt SETREUID 2
.Os BSD 4
.Sh NAME
.Nm setreuid
.Nd set real and effective user ID's
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft int
.Fn setreuid "uid_t ruid" "uid_t 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 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,
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 [EPERM]
.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
.Sh HISTORY
The
.Fn setreuid
system call appeared in
.Bx 4.2 .