NAME

setuid, seteuid, setgid, setegid — set user and group ID

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#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. Supplementary group IDs remain unchanged.

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-group-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

getgid(2), getgroups(2), getuid(2)

STANDARDS

The setuid() and setgid() functions are compliant with the IEEE Std 1003.1-1990 (“POSIX.1”) 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 compliant with IEEE Std 1003.1-2001 (“POSIX.1”).

HISTORY

The setuid() and setgid() functions appeared in Version 2 AT&T UNIX and Version 4 AT&T UNIX, respectively.