set file creation mode mask
Standard C Library (libc, -lc)
umask() 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
to turn off corresponding bits requested in file mode. (See
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
The previous value of the file mode mask is returned by the call.
umask() system call is always successful.
umask() system call is expected to conform to
IEEE Std 1003.1-1990 (“POSIX.1”).
umask() function appeared in
Version 7 AT&T UNIX.