Running out of disk space on my root partition was a bit scary yesterday. “Matt, how did you fill up a 20GB partition in a month’s time??”
After a little searching I found a Debian package for NCDU, a handy disk space visualization tool that runs from the command line.
The results are pretty simple to decipher. Simply navigate using the up, down, and enter keys to find the largest files on the system (that hopefully aren’t system files, but some large log or cache files). In my case it was a 17GB ISO that was in OwnCloud’s “trash” folder, but never got deleted.