tool to alert when files change? [closed]

OS=debian

I have several sites and two users who work on them and sometimes update.

Instead of enabling/disabling the users when the site go live i trust them and assume they wont break my site.

However hackers do exist so i would like an app to alert me when there are changes (i plan to watch all sites that have gone live) so i can check what files are changed and to look at vandalism on the site(s).

The tool should preferably email me.

Bonus if it can tell me when my HD is getting low but i expect to use another tool for that.

You probably want a host based intrusion detection system (IDS) like tripwire since your intent is security. This will generate checksums of files based on the contents. If the file changes next time they are scanned the checksum will differ and will alert you that the file has changed.

You may have noticed that some programs you download contain a md5 hash near the link. This is so you can verify the file integrity. The principle with trip wire is the same.

If you are using Linux, incron will watch files in directories you designate or inotifywait can watch files recursively. Any action can be taken when there are changes.