A small notebook about tools, systems and the web.
Small, documented changes are easier to understand and reverse. Save a working configuration before editing it, change one thing at a time, and check the result from another machine.
A useful maintenance note records what changed, why it changed, how it was checked, and how to restore the previous version.
A backup is most useful when the restore procedure is clear. Keep copies separate from the working files and occasionally restore a sample to a temporary location.
Check both the file contents and the permissions. A readable configuration is only part of a working system.
Ubuntu Server documentation
MDN Web Docs
Linux kernel documentation