umask —
set file
creation mode mask
#include
<sys/types.h>
#include
<sys/stat.h>
mode_t
umask(
mode_t
numask);
The
umask() routine sets the process's file mode
creation mask to
numask and returns the
previous value of the mask. Only the read, write, and execute file permission
bits of
numask are honored, all others are
ignored.
The file mode creation mask is used by the
bind(2),
mkdir(2),
mkdirat(2),
mkfifo(2),
mkfifoat(2),
mknod(2),
mknodat(2),
open(2) and
openat(2) system calls to turn
off corresponding bits requested in the file mode (see
chmod(2)). This clearing allows
each user to restrict the default access to his files.
The default mask value is S_IWGRP|S_IWOTH (022, write access for the owner
only). Child processes inherit the mask of the calling process.
The previous value of the file mode mask is returned by the call.
The
umask() function is always successful.
chmod(2),
mkdir(2),
mkfifo(2),
mknod(2),
open(2)
The
umask() function conforms to
IEEE Std 1003.1-2008
(“POSIX.1”).
The
umask() system call first appeared in
Version 7 AT&T UNIX.