Umask is a number which define the default permissions that is not given on a file or any directory.

How to Calculate Umask:

We can subtract the umask from the base permissions to determine the final permission to any file. Please see below example for more :-

Let's suppose umask 000 It means that User has 0, Group has 0 and other has 0 permission. Now folder permission calculated as :-

User permission is      7-0 =7 (Read, Write and Execute)
Group Permission is   7-0 =7 (Read, Write and Execute)
Other Permission is    7-0 =7 (Read, Write and Execute)

Suppose umask 002 It means that User has 0, Group has 0 and other has 2 permission. Now folder permission calculated as :-

User permission is     7-0 =7 (Read, Write and Execute)
Group Permission is   7-0 =7 (Read, Write and Execute)
Other Permission is    7-2 =5 (Read and Execute)

Suppose umask 022 It means that User has 0, Group has 2 and other has 2 permission Now folder permission calculated as :-

User permission is      7-0 =7 (Read, Write and Execute)
Group Permission is   7-2 =5 (Read and Execute)
Other Permission is    7-2 =5 (Read and Execute)

Suppose umask 027 means User has 0, Group has 2 and other has 2. Now folder permission calculated as :-

User permission is      7-0 =7 (Read, Write and Execute)
Group Permission is   7-2 =5 (Read and Execute)
Other Permission is    7-7 =0 (No permission)

Note : - To Find umask value use below command .

$ umask
output - 0022

To change Umask use this command .

$ umask 072