The Octal Notation And umask

• When we create a new File, the operating system first takes the default permissions ('rw-rw-rw-', or 0666 in octal).
• Then, every bit that is set in the umask, is being cleared in the permissions.
• The resulting number is set as the permissions given to the File.
• This sounds complicated - but after a while you get used to it.
• Eventually, we set a umask in our shell's start-up script, write a comment explaining what it does, and then forget about it.

Originally written by guy keren