| UMASK(2) | System Calls Manual | UMASK(2) | 
umask —
#include <sys/stat.h>
mode_t
  
  umask(mode_t
    numask);
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
  open(2),
  mkdir(2),
  mkfifo(2) and
  mknod(2) to turn off
  corresponding bits requested in 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.
umask() function is always successful.
umask() function conforms to IEEE
  Std 1003.1-1990 (“POSIX.1”).
| June 4, 1993 | NetBSD 10.0 |