Even with our cheap disk storage, we can run out of disk space easily. Also, most filesystems need 15% free disk space to keep optimum performance, as your files will be fragmented, and the system will have to move files arround a lot more to defragment your partitions. And defaults usually require 5% free for the root user to have available in emergencies.
You can buy a new disk, and if you are using LVM you can just add the disk and resize partitions as needed.
To see the largest files in a directory:
ls -Slah | head
To see free disk space
* you must have the partitions mounted that you want
To analyze disk usage
du -h /directory du -h --max-depth=1
* view only one level of current directory - good to start at / to get a good overview of where the space is. can then descend into certain directories and do it again there.
To see a visual representation of relative size:
in KDE, use Konqueror --> FSViewPart
Files that may be safely removed, by distro
- the "work" directory for failed builds, Maybe /var/cache/portage or similar.