DECC$UMASK specifies the default value for the permission mask
    umask. By default, a parent C program sets the umask from the RMS
    default permissions for the process. A child process inherits the
    parent's value for umask.

    To enter the value as an octal value, add the leading zero;
    otherwise, it is translated as a decimal value. For example:

    $ DEFINE DECC$UMASK 026

    Maximum: 0777