getresuid, getresgid - get real, effective, and saved user/group IDs

#define _GNU_SOURCE /* See feature_test_macros(7) */
#include <unistd.h>
int getresuid(uid_t *ruid, uid_t *euid, uid_t *suid);
int getresgid(gid_t *rgid, gid_t *egid, gid_t *sgid);

getresuid() returns the real UID, the effective UID, and the saved set-user-ID of the calling process, in the arguments ruid, euid, and suid, respectively. getresgid() performs the analogous task for the process's group IDs.

On success, zero is returned. On error, -1 is returned, and errno is set to indicate the error.

getuid(2), setresuid(2), setreuid(2), setuid(2), credentials(7)