□ SET Real uid, Effective uid, Saved set-User-ID
□ Function that modifies a process's "real UID", "effective UID" and "saved set-user-ID"
□ Unprivileged process configures each UID as current process's one(=Modification is impossible)
□ Privileged process(=having CAP_SETUID authority) configures each UID as arbitrary values
□ If it is successful it returns 0 and if an error is occured it returns -1