NAME
umask - set file mode creation mask
SYNOPSIS
#include <sys/types.h>
#include <sys/stat.h>
I mode_t umask(mode_t mask );
DESCRIPTION
R umask ()
sets the calling process's file mode creation mask (umask) to
mask
& 0777.
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:
S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH
(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).
SEE ALSO
