I've got an Ubuntu 12.04.2 server whose root partition filled up. I discovered that the /var/log/auth.log file had grown to around 3.8GB. After compressing this file using gzip, the file size was around 110MB.
Running the df -h command, the root partition's disk usage is still at 100%. I'm assuming a reboot will correct this, but since it's a production server, I was wondering if there was a way to convince this server that it actually has much more free space than it thinks.
Thanks in advance for the help and advice.
EDIT: Lesson learned: lsof is your friend!
After running lsof and grepping for auth.log, I was able to determine that another process was using auth.log. After restarting that process, the free space was recognized by the server.