Practical UNIX

Setting Default Permissions for New Files

With the umask command, you can control the permissions of newly created files and directories. To view your current umask value, enter umask with no argument:

$ umask
077
$

To change your umask value, enter the new value as an argument:

$ umask 27

Don’t confuse the umask value with chmod in numeric mode. Here is how umask works.

UNIX wants to create any new file with read/write permission for everyone:

rw-rw-rw-    # default new file permission

It wants to create the same for directories but must also add execute permission so that the directories can be accessed. It does not want to add execute permission for new files until you debug the code:

rwxrwxrwx    # default new directory permission

umask acts like ...