Description

   Initially, the file protection mask is set from the current
   process's default file protection. This is done when the C main
   program starts up or when DECC$CRTL_INIT (or VAXC$CRTL_INIT)
   is called. You can change this for all files created by your
   program by calling umask or you can use chmod to change the file
   protection on individual files. The file protection of a file
   created by open or creat is the bitwise AND of the open and creat
   mode argument with the complement of the value passed to umask on
   the previous call.

                                  NOTE

      The way to create files with OpenVMS RMS default protections
      using the UNIX system-call functions umask, mkdir, creat,
      and open is to call mkdir, creat, and open with a file-
      protection mode argument of 0777 in a program that never
      specifically calls umask. These default protections include
      correctly establishing protections based on ACLs, previous
      versions of files, and so on.

      In programs that do vfork/exec calls, the new process image
      inherits whether umask has ever been called or not from
      the calling process image. The umask setting and whether
      the umask function has ever been called are both inherited
      attributes.