1. Man pages exist and should be used. Seriously, everything’s there, from application docs to syscall docs to syntax and formatting of log files.
2. Don’t reinvent the wheel. 99% of problems you’re experiencing or ever will experience, somebody’s already gone through it and figured it out. Google is your friend.
3. If you don’t know what something’s doing, or why it’s not working, strace it!
4. Logs exist for a reason. Read them.
5. Applications crash, servers don’t. If your server crashes, it’s either bad hardware or a kernel bug (fairly rare on popular distros).
6. Always make backups. Always.
7. Always mount NFS mounts with the ‘intr’ option. Having to reboot because of a network blip is uncool.
8. Learn to use `grep’, `sed’ and `awk’. Learning to manipulate text is surprisingly important for a text-based interface.
9. Load average does not mean CPU usage. 100% memory usage does not mean you don’t have any more available for new applications. You can run out of inodes before you run out of disk space.
10. TCP wrappers suck. If you’ve been hacking at an issue for over 3 hours, look to your TCP wrappers. /etc/hosts, /etc/hosts.allow and /etc/hosts.deny will hold the answer.