set file creation mode mask
routine sets the process's file mode creation mask to
numask and returns the previous value of the mask. The
9 low-order access permission bits of numask are used
by system calls, including
mknod(2) 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.
umask() function is always
chmod(2), mkdir(2), mkfifo(2), mknod(2), open(2)
umask() function conforms to
IEEE Std 1003.1-2008 (“POSIX.1”).
umask() system call first appeared in
Version 7 AT&T UNIX.