apt-cache search
$ sudo apt-cache search ''xpdf''

apt-cache policy
$ sudo apt-cache policy ''xpdf''

apt-cache show
$ sudo apt-cache show ''xpdf''

apt-cache showpkg
$ sudo apt-cache showpkg ''xpdf''

remove package without removing dependencies
$ sudo dpkg -P --force-all liburcu2:amd64

line number in vi/vim
$ :set number

copy file from remote host to the local host directory
$ scp levay@ /home/levay/documents

copy file from local host directory to the remote host directory
$ scp /home/jack/doc/export.text levay@

extract tar file
tar -xvf kakitiga.tar

extract tar.gz (gzip)
tar -xzvf kakitiga.tar.gz

extract tar.gz
tar -xjvf kakitiga.tar.bz2

extract single file called  ‘badak.svg’  from tar archive
tar xzvf kakitiga.tar badak.svg

check file space usages (top 6)
du -hsx * | sort -rh | head -6

clear all buffer cache (pagecache, dentries, and inodes)
$ free && sync && echo 3 > /proc/sys/vm/drop_caches && free

pointer/cursor mouse/touchpad getting stuck, disappear or frozen?
$ sudo modprobe -r psmouse

usb mouse getting stuck or frozen?
$ sudo /etc/init.d/hotplug restart

download full website
$ wget --mirror -p --convert-links -P /home/levay/documents/testing/ http://sherlockholmes.com

format usb drive (to fat32)
umount /dev/sdb1 && mkfs.vfat -n 'liveusb' -I /dev/sdb1

burn iso to usb via command line
dd bs=4M if=BlankOn-9.0-desktop-amd64.iso of=/dev/sdb

display date and time in history command
$ HISTTIMEFORMAT="%d/%m/%y %T" && history