Display Linux distributor's ID
lsb_release -is


Display Linux release number
lsb_release -rs


Display Linux code name
lsb_release -cs


Display machine hardware name
uname -m


List all PCI devices, such as display card and ethernet card.
lspci




Reclaim memory which stores pagecache, dentries and inodes
echo 3 > /proc/sys/vm/drop_caches




Display a list of modules in the Linux Kernel
lsmod




List USB devices
lsusb -v




Display the status of ethernet card
sudo ethtool eth0




List hardware
sudo lshw




List harddisk partitions
sudo fdisk -l




Display SATA harddisk parameters
sudo hdparm -I /dev/sda




Display disk space usage
df -h




Display file/folder space usage
du -bsh FOLDER_NAME




Display amount of free and used memory
free




Display processes
ps -e
Display a tree of processes
pstree
Display processes dynamically
top




Terminate a process with a given process id
sudo kill -9 PROCESS_ID




Terminate all processes with a given name
sudo killall PROCESS_NAME




List files which are opened by a given process
lsof -p PROCESS_ID
lsof -c PROCESS_NAME




List processes which opened a given file
lsof FILE_NAME




List processes which are using port 80
lsof -i :80




Configure an ADSL connection
sudo pppoeconf




Starts up ADSL connections
sudo pon
Shuts down ADSL connections
sudo poff




Display MAC of a given IP address
arping IP_ADDRESS




Display NetBIOS name of a given IP address
nmblookup -A IP_ADDRESS




Display IP address and MAC
ifconfig -a




Display route
netstat -rn




Set MAC of ethernet interface
sudo ifconfig eth0 hw ether 00:11:22:33:44:55




Display information of a domain name
whois example.com




Display the network path to a given host
tracepath example.com




Request an IP address from DHCP server
sudo dhclient




Temporarily restart an init script
sudo /etc/init.d/SCRIPT_NAME restart
Temporarily stop an init script
sudo /etc/init.d/SCRIPT_NAME stop




Add a user
sudo adduser USER_NANE
Delete a user
sudo deluser USER_NAME




Change user password
sudo passwd USER_NAME




Changes user fullname, office number, office extension, and home phone number information.
sudo chfn USER_NAME
Display user information
finger USER_NAME




Temporarily prevent a user from logging in
sudo usermod -L USER_NAME
Revoke the operation above
sudo usermod -U USER_NAME




Add a user to admin group
sudo usermod -G admin -a USER_NAME




Set the HTTP proxy
export http_proxy=http://PROXY.DOMAIN.NAME:PORT




Modify the information displayed after logging in
sudo vim /etc/motd.tail




Choose the input method for X Window
im-switch -c




Convert the file name from GBK to UTF8
convmv -r -f gbk -t utf8 --notest FILE_NAME




Convert the file content from GBK to UTF8
iconv -f gbk -t utf8 FILE_NAME




Convert tags in '*.mp3' from GBK to UTF8
find . -name '*.mp3' -execdir mid3iconv -e GBK {} \;




Read a long file
less FILE_NAME




Print lines matching a pattern
grep REG_EXP FILE_NAME




Display a list of file name. The files contain a given string.
grep -lr REG_EXP PATHNAME




Display all '.txt' file
find . -name '*.txt'




Create two empty files
touch file_name_1 file_name_2




Create directory. Create parent directories as needed.
mkdir -p /tmp/a/b/c/d/e




Change working directory to the home folder
cd
Change working directory to the previous working directory
cd -




Display hidden files
ls -a




Copy directory. Preserve links, file mode, ownership, timestamps. 
cp -a SOURCE_DIRECTORY DEST_DIRECTORY




Determine file type
file FILE_NAME




Output the last 6 lines
tail -n 6 FILE_NAME




Copy files via SSH
scp -rp FILE_NAME USERNAME@HOST:DEST_PATH




Rename '*.rm' files to '*.rmvb' files
rename 's/.rm$/.rmvb/' *




Change the file name to lowercase
rename 'tr/A-Z/a-z/' *




Display subdirectories in current directory
ls -d */.




Display file number in current directory
ls . | wc -w




Extract "*.gz" file
gunzip FILE_NAME.gz
Extract "*.tar.gz" file
tar zxf FILE_NAME.tar.gz
Extract "*.tar.bz2" file
tar jxf FILE_NAME.tar.bz2




Do compression
tar czf FILE_NAME.tar.gz FILE1 FILE2 FILE3
tar cjf FILE_NAME.tar.bz2 FILE1 FILE2 FILE3




Displays a calendar
cal
cal MONTH YEAR




Set the date and time via NTP
sudo ntpdate ntp.ubuntu.com




Poweroff your computer
sudo halt
sudo shutdown -h now
Poweroff your computer in 23:00
sudo shutdown -h 23:00
Poweroff your computer after 60 minutes
sudo shutdown -h +60




Reboot your computer
sudo reboot
sudo shutdown -r now




If you want some program to start up automatically, please put '.desktop' files into '$HOME/.config/autostart'




You can configure "preferred applications" by this file "$HOME/.local/share/applications/mimeapps.list"




Continuously monitor the memory usage
watch -d free




Display HTTP HEAD response
w3m -dump_head http://example.com




Display file content with line number
nl FILE_NAME




Eliminate Rootkit
sudo rkhunter --checkall




Change hostname
sudo hostname new_name




"Tasksel" group software packages into "task"s. You can select a "task" and then install all necessary software packages. It is easy to set up LAMP servers or cloud computing servers.
Show all tasks
tasksel --list
Display the extended description of a task
tasksel --task-desc lamp-server
List the packages which are parts of a task
tasksel --task-packages lamp-server
Install/remove a task
gksudo tasksel




Change Process priority
renice NEW_PRIORITY `pgrep NAME_OF_PROCESS`
example: renice 5  `pgrep firefox`     
         renice -5 `pgrep wine-server`       
               high <------------------> low
NEW_PRIORITY = -19, -18, -17 [...] 18, 19, 20




Clear Bash history
history -c


If you want to use colorful "ls", that is, use colors to distinguish types of files, you can add these lines in $HOME/.bashrc:


if [ "$TERM" != "dumb" ]; then
    eval "`dircolors -b`"
    alias ls='ls --color=auto'
fi


Set apt source
sudo software-properties-gtk
sudo software-properties-kde


Display the packages which are not installed but have remained residual config
dpkg -l | awk '/^rc/ {print $2}'




Add a PPA repository:
sudo add-apt-repository ppa:PPA-REPOSITORY-NAME




Display a list of files. The files are installed from a given package.
dpkg -L PACKAGE_NAME




Display a list of packages. The packages installed a given file.
dpkg -S FILE_NAME




Display a list of packages. The name of packages matches given regex pattern.
apt-cache search REG_EXPRESSION




Display a list of packages. The packages provide a given file.
apt-file search FILE_NAME




Display a list of packages. The given package depends on the list of packages.
apt-cache depends PACKAGE_NAME




Display a list of packages. These packages depend on the given package.
apt-cache rdepends PACKAGE_NAME




Prompt for a disk to be inserted and then add the disc to the source list.
sudo apt-cdrom add




Install the newest versions of all packages currently installed on the system.
sudo apt-get upgrade




Delete residual package configuration files.
dpkg -l | grep ^rc | awk '{print $2}' | sudo xargs dpkg -P




Automatically install necessary files for './configure ; make ; make install'
sudo auto-apt run ./configure




Save the list of packages currently installed on your system.
dpkg --get-selections | grep -v deinstall > SOME_FILE
Then use the file to restore packages. 
dpkg --set-selections < SOME_FILE ; sudo dselect




After running "sudo apt-get install", "*.deb" files are stored in "/var/cache/apt/archives"
You can clean this directory by:
sudo apt-get clean




Display URL for a given package
apt-get -qq --print-uris install PACKAGE_NAME




Display some statistics about the apt cache
apt-cache stats




Display all package name
apt-cache pkgnames




Display some information of a given package
apt-cache show PACKAGE_NAME






"Beri seorang seekor ikan dan ia dapat makan untuk satu hari, tetapi jika anda mengajarkan dia bagaimana untuk memancing, maka dia akan makan untuk seumur hidup"
- Ailurus -