Print the current value of the file creation mode mask, or set it to value , a three-digit octal code specifying the read-write-execute permissions to be turned off. This is the opposite of chmod . Normally used in .login or .profile . umask is a built-in command in the Bourne, Korn, and C shells (see Chapter 4 and Chapter 5 ).
Turn off write permission for others:
umask 002 Produces file permission -rw-rw-r--
Turn off all permissions for group and others:
umask 077 Produces file permission -rw-------
Note that you can omit leading zeroes.