How to clean up unnecessary files

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http://unix.stackexchange.com – Please suggest me any particular unnecessary file that I can clean to back everything to normal condition(temporarily). (i.e. any log or archieve or anything ). My var/log has only 40MB and Home directory has 3GB of space(so I believe that's not a problem). Other than that what I can clean up to make space. [user@host]$ df -h Filesystem Size Used Avail Use% Mounted on /dev/mapper/vg_inamivm-lv_root 18G 17G 0 100% / tmpfs 1.9G 0 1.9G 0% /dev/shm /dev/sda1 485M 71M 389M 16% /boot I am in a debian machine. UPDAT (HowTos)