setuid(2) System Calls Manual setuid(2) setuid - (libc -lc) #include int setuid(uid_t uid); setuid() . (: CAP_SETUID ) UID . setuid() POSIX _POSIX_SAVED_IDS. set-user-ID ( root) . root set-user-ID-root : setuid() uid. root. set-user-ID-root root root setuid(). seteuid(2). . -1 errno . : setuid() UID 0 setuid(). EAGAIN UID ( uid UID ) . EAGAIN uid uid RLIMIT_NPROC . 3.1 ( ) EAGAIN execve(2). EINVAL uid . EPERM (: CAP_SETUID ) uid UID . C . POSIX . NPTL POSIX UIDs GIDs . ( setuid()) . nptl(7). POSIX.1-2024. POSIX.1-2001 SVr4. 4.4BSD . setuid() 16-bit . 2.4 setuid32() 32-bit. setuid() glibc . . setuid() . setfsuid(2). uid UID . getuid(2), seteuid(2), setfsuid(2), setreuid(2), capabilities(7), credentials(7), user_namespaces(7) 3 . . : . 6.18 8 2026 setuid(2)