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.\"     @(#)setuid.2	8.1 (Berkeley) 6/4/93
.\"
.TH SETUID 2 "16 January 1996" GNO "System Calls"
.SH NAME
.BR setuid ,
.BR seteuid ,
.BR setgid ,
.BR setegid ,
\- set user and group ID
.SH SYNOPSIS
#include <sys/types.h>
.br
#include <unistd.h>
.sp 1
int
\fBsetuid\fR (uid_t \fIuid\fR);
.br
int
\fBseteuid\fR (uid_t \fIeuid\fR);
.br
int
\fBsetgid\fR (gid_t \fIgid\fR);
.br
int
\fBsetegid\fR (gid_t \fIegid\fR);
.SH DESCRIPTION
The
.BR setuid 
function
sets the real and effective
user IDs and the saved set-user-ID of the current process
to the specified value.
The
.BR 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.
.LP
The
.BR setgid 
function
sets the real and effective
group IDs and the saved set-group-ID of the current process
to the specified value.
The
.BR 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.
.LP
The
.BR seteuid 
function
sets the effective user ID (group 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
.BR intro (2)
and
.BR 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, the effective group ID may be set to the value
of the real group ID or the saved set-user-ID.
.LP
.SH RETURN VALUES
Upon success, these functions return 0;
otherwise \-1 is returned.
.LP
If the user is not the super user, or the uid
specified is not the real, effective ID, or saved ID,
these functions return \-1.
.SH SEE ALSO
.BR getuid (2),
.BR getgid (2)
.SH STANDARDS
The
.BR setuid 
and
.BR setgid 
functions are compliant with the
POSIX 1003.1-88
specification with _POSIX_SAVED_IDS not defined.
The
.BR seteuid 
and
.BR setegid 
functions are extensions based on the POSIX
concept of _POSIX_SAVED_IDS,
and have been proposed for a future revision of the standard.