$ uname –a # display linux system information
  $ uname –r # display kernel release information
  $ uptime # show how long system running + load
  $ hostname # show system host name
  $ hostname -i # display the IP address of the host
  $ last reboot # show system reboot history
  $ date # show the current date and time
  $ cal # show this month calendar
  $ w # display who is online
  $ whoami # who you are logged in as
  $ finger user # display information about user
  $ lsb_release -d # display ubuntu version

  Terminal related
  $ reset # Reset the terminal if display fucks
  $ stty insane # if previous doesn't work

  $ dmesg # detected hardware and boot messages
  $ cat /proc/cpuinfo # CPU model
  $ cat /proc/meminfo # hardware memory
  $ cat /proc/interrupts # lists the number of interrupts per CPU per I/O device
  $ lshw # displays information on hardware configuration of the system
  $ lsblk # displays block device related information in Linux
  $ free -m # used and free memory (-m for MB)
  $ lspci -tv # show PCI devices
  $ lspci -nnk | egrep -iA3 "VGA" # display graphic driver information
  $ lsusb -tv # show USB devices
  $ lshal # show a list of all devices with their properties
  $ dmidecode # show hardware info from the BIOS
  $ hdparm -i /dev/sda -show info about disk sda
  $ hdparm -tT /dev/sda # do a read speed test on disk sda
  $ badblocks -s /dev/sda # test for unreadable blocks on disk sda

  $ top # display and update the top cpu processes
  $ mpstat 1 # display processors related statistics
  $ vmstat 2 # display virtual memory statistics
  $ iostat 2 # display I/O statistics (2sec Intervals)
  $ tail -n 500 /var/log/syslog # last 10 kernel/syslog messages
  $ tcpdump -i eth1 # capture all packets flows on interface eth1
  $ tcpdump -i eth0 'port 80' # monitor all traffic on port 80 ( HTTP )
  $ lsof # list all open files belonging to all active processes
  $ lsof -u testuser # list files opened by specific user
  $ free –m # show amount of RAM
  $ watch df –h # watch changeable data continuously

  $ id # show the active user id with login and group
  $ last # show last logins on the system
  $ who # show who is logged on the system
  $ groupadd admin # add group "admin" (force add existing group)
  $ useradd -c "Joe Smith" -g admin -m joe # Create user "joe" and add to group "admin"
  $ userdel joe # delete user joe (force,file removal)
  $ adduser joe # add user "joe"
  $ usermod # modify user information

  $ gpg -c file # encrypt file
  $ gpg file.gpg # decrypt file
  $ iconv -f UTF-8 -t UTF-17 fichier.txt >> new-encodage.txt

  Binaries
  $ ldd binary-path # list shared object dependencies
  $ ldconfig -p # list all libs in current cache

  $ ps # display your currently active processes
  $ ps -e # display all active processes
  $ ps f # display your currently active processes in a tree way
  $ ps aux | grep 'telnet' # find all process id related to telnet process
  $ pmap # memory map of process
  $ top # display all running processes
  $ kill pid # kill process with mentioned pid id
  $ killall proc # kill all processes named proc
  $ pkill processname # send signal to a process with its name
  $ bg # resumes suspended jobs without bringing them to foreground
  $ fg # brings the most recent job to foreground
  $ fg n # brings job n to the foreground

  $ chmod octal file-name # change the permissions of file to octal , which can be found separately for user, group and world; octal value 4 -read 2 –write 1 –execute
  $ chown owner-user file # change owner of the file
  $ chown owner-user:owner-group file-name # change owner and group owner of the file
  $ chown owner-user:owner-group directory # change owner and group owner of the directory

  $ ifconfig –a # display all network ports and ip address
  $ ifconfig eth1 mtu 9000 up # set mtu to 9000
  $ ifconfig eth0 # display specific ethernet port ip address and details
  $ ifconfig -a | grep HWaddr # display MAC address

  change MAC address:
  # ifconfig eth0 down
  # ifconfig eth0 hw ether 00:80:48:BA:d1:30
  # ifconfig eth0 up

  $ ip addr show # display all network interfaces and ip address (available in iproute2 package,powerful than ifconfig)
  $ ip address add 192.168.0.1 dev eth0 # set ip address
  $ ethtool eth0 # linux tool to show ethernet status (set full duplex , pause parameter)
  $ mii-tool eth0 # linux tool to show ethernet status (more or like ethtool)
  $ ping host # send echo request to test connection (learn sing enhanced ping tool)
  $ whois domain # get who is information for domain
  $ dig domain # get DNS information for domain (screenshots with other available parameters)
  $ dig -x host # reverse lookup host
  $ host google.com # lookup DNS ip address for the name
  $ nslookup google.com # lookup DNS information for the name
  $ hostname –i # lookup local ip address (set hostname too)
  $ wget file # download file (very useful other option)

  WiFi related:
  $ iwconfig wlan0 essid "mynetworkESSID" # specify ESSID for the WLAN
  $ dhclient wlan0 # to receive an IP address, netmask, DNS server and default gateway from the Access Point
  $ iwconfig wlan0 mode managed key [WEP key] # 128 bit WEP use 26 hex characters, 64 bit WEP uses 10
  $ iwconfig wlan0 mode master # set the card to act as an access point mode
  $ iwconfig wlan0 mode managed # set card to client mode on a network with an access point
  $ iwconfig wlan0 mode ad-hoc # set card to peer to peer networking or no access point mode
  $ iwconfig wlan0 mode monitor # set card to RFMON mode
  $ iwconfig wlan0 essid any # with some cards you may  disable the ESSID checking
  $ iwconfig wlan0 key 1111-1111-1111-1111 # set 128 bit WEP key
  $ iwconfig wlan0 key off # disable WEP key
  $ iwconfig wlan0 key open # sets open mode, no authentication is used and card may accept non-encrypted sessions
  $ iwlist wlan0 scan # give the list of Access Points and Ad-Hoc cells in range (ESSID, Quality, Frequency, Mode etc.)
  $ iwlist wlan0 power # list the various Power Management attributes and modes of the device
  $ iwlist wlan0 txpower # list the various Transmit Power available on the device
  $ iwlist wlan0 retry # list the transmit retry limits and retry lifetime on the device

  Sockets related
  $ netstat -lntup # Display a listing of all active listening ports
  $ ss -aE # Continually display state of sockets
  $ lsof -i # List of all internet and x.25 network files

  $ rpm -i pkgname.rpm # install rpm based package
  $ rpm -e pkgname # remove package

  $ grep pattern files # search for pattern in files
  $ grep -r pattern dir # search recursively for pattern in dir
  $ locate file # find all instances of file
  $ find /home/tom -name 'index*' # find files names that start with "index"
  $ find /home -size +10000k # find files larger than 10000k in /home

  $ rsync -a /home/apps /backup/ # synchronize source to destination
  $ rsync -avz /home/apps gordon@192.168.10.1:/backup # synchronize files/directories between the local and remote system with compression enabled

  $ df –h # show free space on mounted filesystems
  $ df -i # show free inodes on mounted filesystems
  $ fdisk -l # show disks partitions sizes and types
  $ du -ah # display disk usage in human readable form
  $ findmnt # displays target mount point for all filesystem
  $ mount device-path mount-point # mount a device

  Alt+Ctrl+T # open Terminal Window

  Alt+Ctrl+L # lock the screen
  Alt+Ctrl+Del # logoff

  Alt+F4 # close current window
  Alt+F2 # pop up command window (for quickly running commands)

  Super-W  # show all windows in the current workspace
  Ctrl+Super+D # show desktop

  Ctrl+A # select all items on list or text
  Ctrl+C # copy all selected items to clipboard
  Ctrl+X # cut all selected items to clipboard
  Ctrl+V or Mouse middle button click # paste all selected items to clipboard

  PrintScr # takes screenshot
  Alt+PrintScr # takes screenshot of windows
  Shift+PrintScr # takes screenshot of selected window area