I have a ubuntu server with smbd ftp and a http server. For some reason the freedisk space will go from 2 gb down to 0 bytes as time goes on (usually a couple of days). However once i reboot, the disk space jumps back up.
What is the problem?
The problem will probably be the /tmp directory is filling up - rebooting clears this directory out. You may want to have a look in it and see what files are created (session cookies ?) and then target the program that is creating the offending file(s).
You can delete these files periodically though Cron, however it may not be a good idea to do it if the program that relies on it is still running - that will, of-course, depend entirely on the program.
(Technically its possible to delete the files using 1 liner in CRON - I don't recommend it, but something like the following might work, with some tweeking)
0 * * * * find /tmp -ctime +1 -name "offendingfiles.*" -exec rm {} +
This will find any files which match "offendingfiles.*" in the /tmp directory greater then 1 day old and remove them.
A better way for handling log files - if that is where the problem lies, which I think is a bit unlikely, would be to modify the rotation, compression and deletion of the files (edit /etc/logrotate.conf and/or /etc/logrotate.d/*)
/var/log
and/tmp
.