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.\"     @(#)setuid.2	8.1 (Berkeley) 6/4/93
.\"
.Dd June 4, 1993
.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 effective user ID is that of the super user,
or if the specified user ID is the same as the effective user ID.  If
not, but the specified user ID is the same as the real user ID,
.Fn setuid
will set the effective user ID to the real user ID.
.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 effective user ID is that of the super user,
or if the specified group ID is the same as the effective group ID.  If
not, but the specified group ID is the same as the real group ID,
.Fn setgid
will set the effective group ID to the real group ID.
.Pp
The
.Fn seteuid
function
.Pq Fn setegid
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
.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, the effective group ID may be set to the value
of the real group ID or the saved set-user-ID.
.Pp
.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
specified is not the real, effective ID, or saved ID,
these functions return \-1.
.Sh SEE ALSO
.Xr getuid 2 ,
.Xr getgid 2
.Sh STANDARDS
The
.Fn setuid
and
.Fn setgid
functions are compliant with the
.St -p1003.1-90
specification with
.Li _POSIX_SAVED_IDS
defined, with the extensions allowed in section B.4.2.2.
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.