Perintah-perintah penting dalam OS linux

Add a user
sudo adduser USER_NAME
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
 

Clear Bash history
history -c

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
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 '~/.config/autostart'

You can configure "preferred applications" by this file "~/.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

~/.thumbnails/ directory is a cache dir GNOME makes when you browse through your folders in nautilus.
It contains thumbnail pictures of picture files you've previously looked at.You can get its total size by
du -bs ~/.thumbnails/

You can delete the files in the .thumbnails directory that haven't been accessed for seven days, to free disk space.
find ~/.thumbnails/ -type f -atime +7 -exec rm {} \;

Capture screen after 10 seconds
gnome-screenshot -d 10
Capture current window after 10 seconds
gnome-screenshot -wd 10

Start GConf editor:
Press Alt+F2, type 'gconf-editor'.

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