Chapter 6. Basic System Security
One of the most critical tasks performed by system administrators is setting up and monitoring system security. Debian provides some assistance here, with special packages that help in hardening your systems, but this is only the beginning. In particular, you must pay attention to how you set up the root account, how to block improper access to your systems, and how to monitor your system for security problems.
One of the first things to consider is how to set up user groups and how to manage the root account. Although this can be changed any time, it should be done just after installation when changes will have less impact. The two basic issues are how to set up default user group assignment, ...