Calculating default permission
1. file – Maximum allowed permission at the time of file creation (666)
Default permission on a file
1st zero is special permission
2nd zero is owner perm.
Max. allowed permission at the time if dir creation (777)
Default permission on a dir.
Set the value of umask such that file created after changing umask value have read & write perm. for owner but no permission to group members & others.
-sets value of umask for the curent session
3rd zero group perm.