find which process is using a deleted file
lsof +L1

ok this is cool but even if you deleted the file, the process still owns a handler to this file, and in some situations we don't want to kill the process. Here's a workaround using deletion of the file handler :
go to the process folder
cd /proc/PID/fd

ls -l |grep deleted
take note of the file handler ID. e.g here below the file handler is 1.
l-wx------ 1 hudson devel 64 Feb  7 11:48 1 -> /crucible/data/current/var/log/fisheye.out (deleted)

reclaim the space
> 1