My /home directory was getting filled.
I tried to make space but the space was occupied straight away.
I found a 8.8G file in /home/user/ :
-rw------- 1 user adm 8.8G 2016-01-16 10:16 .xsession-errors
I deleted it but the space was filling up again.
In iotop, I found the process that was filling it (process with highest DISK WRITE speed).
I killed it, and the growth stopped, but I didn't reclaim the space.
the process was knotify or knotify4.
iotop does not leave any output on the console, so I am not sure.