Linux Security Measures

1. chmod 400 /etc/shadow
2. chmod 400 /etc/gshadow
3. Modify /etc/ssh/sshd_config to mark 'PermitRootLogin' as 'no'
4. Modify /etc/securetty file to limit the number of shells that the root user can use for login.
5. chmod 644 /etc/profile (ensure owner is root)
6. chmod 644 /etc/environment (ensure owner is root)
7. Modify /etc/shells to keep only /bin/bash shell
8. Modify /etc/passwd for users default shell