File Permissions

Question 1

For ‘chmod’, what is the difference between ‘x’ and ‘X’?

Answer 1

■ ‘x’ sets the execute bit on a file

■ ‘X’ sets the execute bit on a directory or a file that has the execute bit

Question 2

Who is allowed to change the ownership of a file?

Answer 2

■ Only root can change the ownership of a file. Group ownership can be set by either the file owner or root.

Question 3

What does the ‘setuid’ (suid) (+s) mean on an executable file?

Answer 3

■ ‘setuid’ causes the file to be executed as the user (owner) of the file and not as the user that ran the command.

Question 4

What does the ‘setgid’ (sgid) (+s) mean on an executable file?

Answer 4

■ ‘setgid’ causes the file to be executed as the group owner of the file and not as the user that ran the command.
■ Files newly created in the directory have their group owner set to match the group owner of the directory.

Question 5

What does the ‘sticky bit’ mean on a directory?

Answer 5

■ It means only the file owner and root can change/delete a file. Users have no change/delete rights to files not their own.

Question 6

What does the command ‘umask’ do?

Answer 6

■ Set the permissions for newly created files and directories.

Question 7

Where are the default system ‘umask’ values set?

Answer 7

■ /etc/profile

■ /etc/bashrc

Question 8

What files must a user edit to change their own ‘umask’?

Answer 8

■ .bash_profile

■ .bashrc

Question 9

How are ACL settings indicated on a file or directory?

Answer 9

■ ‘+’ is appened to the permissions column

■ Example: -rwxrw—-+

Question 10

Which set of permissions are shown when ACL settings are set?

Answer 10

■ ACL settings instead of traditional POSIX settings.

Question 11

Whom does the ACL mask affect?

Answer 11

■ The ACL mask defines the maximum permissions that can be granted to ‘named users’, the ‘group-owner’, and ‘named groups’. It does not restrict the permissions of the ‘file owner’ or ‘other’ users.