Safe to kill all user: 'nobody' processes?
 

Is it safe to kill all processes which have the user: "nobody"? I set up a firewall but it doesn't seem to stop them. Is it online_update which starts these processes or is it some trojan horse/virus? I could write a program which kills all nobody-processes every other minute and sleeps the rest of the time. The processes are using up all CPU capacity.

The "nobody" user may be the result of a process downgrading its permissions. I don't think that blindly killing processes is a good idea. Looking at firewall log entries and hunting for rootkits may be a better idea.

What if cron would run updateDB when recording?
 

I plan to install MythTV. What if cron were to run some updateDB-script when I was recording TV? All CPU power is occupied. Sometimes the mouse-cursor won't even move and it goes on for hours.

Cron jobs will always run as the user whos crontab they are in, or root if they are in /etc/cron.daily, etc. If you are concerned about them eating CPU cycles, prefix the commands with nice, which basically assigns the process the lowest possible priority. See man nice for details.

FWIW, there are many processes that run as "nobody." Apache is probably the most common one. Under a default 2.0.x install, all Apache processes run as user nobody, group nobody. Its nothing to worry about from a security perspective.

The updatedb script updates the locate database - ie. the list of all files on your computer - so that you can use the locate command to quickly find files. You can safely disable this feature (you probably don't use it if you didn't know what it is) and you can still use the find command or the find files dialog in Konqueror (or nautlius if you use GNOME) to find files still. Its a very good idea to disable things like this if you're setting up a MythTV box.