SETUID(2) MachTen Programmer’s Manual SETUID(2)

NAME
setuid, seteuid, setgid, setegid, - set user and group ID

SYNOPSIS
#include <sys/types.h>
#include <unistd.h>

int
setuid(uid_t uid)

int
seteuid(uid_t euid)

int
setgid(gid_t gid)

int
setegid(gid_t egid)

DESCRIPTION
The setuid() function sets the real and effective user IDs and the saved
set-user-ID of the current process to the specified value. The 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.

The setgid() function sets the real and effective group IDs and the saved
set-group-ID of the current process to the specified value. The 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.

The seteuid() function (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 intro(2) and 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.

RETURN VALUES
Upon success, these functions return 0; otherwise -1 is returned.

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.