umask(2) System Calls Manual umask(2) umask - (libc -lc) #include mode_t umask(mode_t mask); umask() (umask) mask & 0777 ( mask) . open(2) mkdir(2) umask . umask mode open(2) mkdir(2). (ACL) ( acl(5)) umask mode. umask 022: u::rwx,g::r-x,o::r-x mode 0666 (rw-rw-rw-) 0644 (rw-r--r--). masks inode(7). umask S_IWGRP | S_IWOTH ( 022). mode open(2) : S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH ( 0666) : S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH ( 0666 & ~022 = 0644 rw-r--r--). . POSIX.1-2008. POSIX.1-2001 SVr4 4.3BSD. fork(2) umask . umask execve(2). umask() umask . umask() . (races) . 4.7 umask Umask /proc/pid/status. /proc/self/status umask . umask POSIX IPC (mq_open(3) sem_open(3) shm_open(3)) (FIFOs) (mkfifo(3)) (unix(7)) . umask System V IPC ( msgget(2) semget(2) shmget(2)). chmod(2), mkdir(2), open(2), stat(2), acl(5) 3 . . : . 6.18 8 2026 umask(2)