umask()
sets the calling process's file mode creation mask (umask) to
mask
& 0777 (i.e., only the file permission bits of
mask
are used), and returns the previous value of the mask.
The umask is used by
open(2),
mkdir(2),
and other system calls that create files
to modify the permissions placed on newly created files or directories.
Specifically, permissions in the umask are turned off from
the mode argument to
open(2)
and
mkdir(2).
The constants that should be used to specify
mask
are described under
stat(2).
The typical default value for the process umask is
S_IWGRP | S_IWOTH
(octal 022).
In the usual case where the
mode
argument to
open(2)
is specified as:
(octal 0666) when creating a new file, the permissions on the
resulting file will be:
S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH
(because 0666 & ~022 = 0644; i.e., rw-r--r--).
RETURN VALUE
This system call always succeeds and the previous value of the mask
is returned.
CONFORMING TO
SVr4, 4.3BSD, POSIX.1-2001.
NOTES
A child process created via
fork(2)
inherits its parent's umask.
The umask is left unchanged by
execve(2).
The umask setting also affects the permissions assigned to POSIX IPC objects
(mq_open(3),
sem_open(3),
shm_open(3)),
FIFOs
(mkfifo(3)),
and Unix domain sockets
(unix(7))
created by the process.
The umask does not affect the permissions assigned
to System V IPC objects created by the process (using
msgget(2),
semget(2),
shmget(2)).
This page is part of release 3.14 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
