file /var/log/syslog eats my hard drive

It happened to me before that I was filling my disk with log files from my experiments, but this time it was not connected to any of my activities… Ubuntu 16.04 halts and did not resume normal operation. After a hard reset, the system booted and I explored the problem.

0 byte of free disk space

I figured out that I had no space left on my hard-drive. Ok, let’s see what occupies the space using the linux disk usage analyzer.
sudo baobab
Since not even the auto-completion in the terminal works without space on the disk, I quickly decided to delete some old junk to free some GB.

The newly freed space was eaten at 10 MB/s

No time to waste… the disk was just filling up again.
showed that a process rsyslog was occupying one CPU
sudo iotop
revealed that rsyslog was writing with 10 MB/s to the disk. A quick search pointed me to the files in /var/log.

/var/log/syslog occupied more than 20 GB

Deleting some other old files from my computer made it obvious: syslog was growing rapidly as soon as space was available.

Freeing space without destroying my system

It is never a good idea to blindly delete large system files on your computer. To empty these logfiles, the following works found here:

sudo su
> /var/log/syslog

But what was logging 10 MB/s

tail /var/log/syslog
Showed me the following messages:

Dec 10 22:59:25 behrejan org.freedesktop.FileManager1[6082]: page: Error: /home/behrejan/texmf/fonts/tfm/public/cm/cmr10.tfm: File corrupted, or not a TFM file
Dec 10 22:59:25 behrejan org.freedesktop.FileManager1[6082]: page: Warning: font `cmr10' not found, trying metric files instead

htop showed that the evince thumbnailer used one core of my machine trying to create a thumbnail of an dvi document complaining that a latex font cmr10.tfm is not available.
Fix: Open the file. It will create the thumbnail and the thumbnailer is quiet. Second option: delete/compress the dvi file and kill evince thumbnailer (e.g., using htop).