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.

SEE ALSO
getuid(2), getgid(2)

STANDARDS
The setuid() and setgid() functions are compliant with the p1003.1-90 specification with _POSIX_SAVED_IDS not defined. We do not implement the _POSIX_SAVED_IDS option as specified in the standard because this would make it impossible for a set-user-ID executable owned by a user other than the super-user to permanently revoke its privileges.

The seteuid() and setegid() functions are extensions based on the POSIX concept of _POSIX_SAVED_IDS, and have been proposed for a future revision of the standard. They provide the same feature of toggling effective IDs as _POSIX_SAVED_IDS, but do so independent of the current effective ID, rather than requiring the super-user to permanently revoke its privileges.