Question

3. Explain the differences among the following unmask values: 077, 027, 022, and 755. How would you set one of these values as a site-wide default for new users? Can you impose an unmask standard on your users?

Answer 1

What is umak?

In linux/unix, the user file-creation mode mask (umask) is used to determine file permissions for newly created files or folders. Generally we use umask to control the default file permission.

How to calculate Umask:
The octal umasks assigned based on bitwise AND of the unary complement of the argument using bitwise NOT.
The values are as follows:

Octal value : Permission
0 : read, write and execute
1 : read and write
2 : read and execute
3 : read only
4 : write and execute
5 : write only
6 : execute only
7 : no permissions

So as per above,

027: By default permission for file is 640 and directory 750 other have no permissions.
022: Generally it is used for root user.Directory permissions are 755 and file permissions are 644.
077: This umask is for private. No other user can read or write data.

How to set umask?
We can setup umask in /etc/bashrc or /etc/profile file.
Commands to set umask:

# vi /etc/profile
umask 022