1. Use SELinux
SELinux is a security enhancement to Linux, which allows users and administrators more control over access control. SELinux adds finer granularity to access controls. Instead of only being able to specify who can read, write or execute a file, for example, SELinux lets you specify who can unlink, append only, move a file and so on.
2. Subscribe to a Vulnerability Alert Service
Your operating system may not necessarily be the one that is vulnerable. In fact, vulnerabilities are most often found in the applications that one installs. In order to avoid this, you must keep your applications updated to the newest version. In addition, subscribe to alert services like SecurityFocus.
3. Disable Unused Services and Applications
In general, users do not use half of the services and applications on their system for most of the time. These services and applications though are kept running, which could make for an invitation to attackers. It is best to keep unused services stopped.
4. Check System Logs
Your system logs tell you what activity has happened on the system, including whether an attacker has been successful in or tried to access the system. Being careful is your first line of defense and your system logs should be regularly monitored for this.
5. Consider Port Knocking
Setting up port knocking is a good way to establish a secure connection with a server. What basically happens is that a special package is sent to the server, which triggers a response/connection from the server. Port knocking is a good defensive manuever for those who have open ports on their systems.
6. Use Iptables
What is Iptables? This is an application framework, which allows the user to write their own powerful firewall for the system. So, learn how to write a good firewall and use the Iptables framework in order to do well.
7. Deny All by Default
Firewalls follow two philosophies: one is to allow every bit of traffic and the other is to deny access to everything, prompting you for permission. The second option is the better of the two. You should only allow the traffic that is important to come in.
8. Use an Intrusion Detection System
An Intrusion Detection System or IDS allows you to manage the traffic and attacks on your system better. Snort is arguably the best IDS for Linux that is available today.
9. Use Full Drive Encryption
Encrypted data is harder and sometimes impossible to steal, which is why you should keep your entire drive encrypted. This way if someone does get access to your system, they will still have a very hard time getting by the encryption. According to some reports, most data loss is through stolen machines.
