But are there any common cases of what can consume so much space? And what is safe to delete and what not, is there any FAQ on it?Alright then this is how you should proceed:
du -ah --max-depth=1 /
It will show you the disk usage for all directories at / partition. So cd into the folder that is consuming the maximum space and run du -ah --max-depth=1 sitting there and so on...
Note that log rotation is built into cpanellogd and suexec log rotation was introduced in recent builds. Is cpanellogd running on your server? If not, that can lead to logs filling up the hard drive, and if the logs get over 2 GB in size, software (most notably, Apache) can begin malfunctioning.Some time ago i opened a thread about this issue.
cPanel has a major bug, or at least a problem that nobody is willing to fix, even though we've opened a bug report.
basically, after a few months or a year, your server will consume all its disk space because cPanel doesn't clean up after itself.
Here are a few things we found:
1) /etc/httpd/logs, some logs like the "suexec_log" are not rotated. Also, some /etc/httpd/domlogs/*ssl* are also not rotated. We've added a bunch of lines in logrotate to fix that.
2) /home/.cpan and /home/.cpcpan, those will consume GIGs or terabytes with garbage and old data files. We've added a bunch of cron jobs to delete both directories once a week.
Other popular directories with trash, include /usr/local/cpanel/3rdparty, but i can't be sure what you can delete from there.
So far cPanel developers have been ignoring this and refuse to make their update script clean up after it self, that should have solved the problems in /home/.cpan.