In this chapter we discuss basic Linux system security. Security is unfortunately a topic of ever-growing importance, especially with the increasing use of permanently network-connected systems that are vulnerable to remote attacks even while unattended.

Most system security is commonsense good practice. Many of the best techniques are the simplest, yet frequently ignored practices; we cover those first. We then move on to some of the less obvious practices, and we conclude with a short discussion of the complex subject of network security. We also include some firewall recipes to protect simple installations against network attack.