SOLVED - Ubuntu server - Wrong Used Disk Space. Does the quota allocated in ISPCONFIG for website and mails are calculated as used disk space. My file system on ubuntu server shows 27.4GB, but on the top line of Disk Usage Analyzer shows - 157.9GB used and available 62GB. while exploring in documents it shows only - 50.8GB free. The usage report is really misleading.
Filesystem Size Used Avail Use% Mounted on /dev/sda1 220G 158G 51G 76% / none 1.9G 280K 1.9G 1% /dev none 1.9G 200K 1.9G 1% /dev/shm none 1.9G 348K 1.9G 1% /var/run none 1.9G 0 1.9G 0% /var/lock none 1.9G 0 1.9G 0% /lib/init/rw
Solved /root/.local/share/Trash/files running the command - gksudo dbus-launch nautilus and then clicking on trash icon and then empty trash does the trick. I recovered 102GB of space.