Umask

umask is the way the UNIX operating system determines what default permissions that files and directories are created with.

The mask itself is applied as a bitwise AND operation then a bitwise NOT of that with the default 777 permisions eg.,

    777
AND NOT 022
  = 755

The three popular umasks are 022, 002 and 000.

022

This as the example shows above that you will get full rwx for the user, r-x for the group and r-x for other. This is the default in almost all of our operating systems.

002

This would give full rwx for the user, full rwx for the group and give only r-x for other. This is helpful when you want your default group (or a SetGID directory) to have full control over the files and directories you create while allowing everyone else read and execute permissions.

000

This is the most restrictive umask and gives no permissions