Command

At Shell Prompt

• Running previous command with sudo:

  ls -la
  sudo !!
  

  Usage: This will run ls -la command using sudo command

• Using !! on shell prompt:

  ls -la a
  echo !!:2
  

  Usage: This will print a on screen.

• Using !! to replace some part of command:

  echo "foo"
  !!:gs/foo/bar
  

  Usage: Runs previous command replacing foo by bar every time that foo appears

• whoami in mysql database:

  mysql> select user(),current_user();
  

Perl

• Edit file contents:

  perl -pi.bak -e "tr/[a-z]/[A-Z]/" sample.txt
  

  Usage: Creates backup of original file and replace text in given file.

• Replace text in file and creating backup of file:

  perl -pi.bak -e '<replacement>' <filename>
  

  Usage: perl -pi.bak -e ‘tr/[a-z]/[A-Z]/g’ sample.txt

  This will convert text of sample.txt to uppercase and create backup of sample.txt as sample.txt.bak

Process

• Find infomartion about process by name:

  ps ax | grep <process_name>
  ps ax | grep <process_name> | grep -v grep
  

  Usage:

  • ps ax | grep apache2
  • ps ax | grep [Aa]pache2 #This will only show apache process (without grep)
  • ps ax | grep apache2 | grep -v grep

Networking

• Shows the network connections:

  ifconfig
  

• Show ip address for all available interfaces:

  ip addr | grep inet
  

• Start webserver serving current directory tree at http://localhost:8000/:

  python -m SimpleHTTPServer
  

• Find who owns port number:

  fuser -v -n tcp <port_number>
  

  Usage: fuser -v -n tcp 6000

Kernel and Kernal module

• Shows the status of modules in the Linux Kernel:

  lsmod
  

• Shows the list of modules for Linux Kernel:

  ls /lib/modules/$(uname -r) -R  | grep ko
  

• Finding hardware information:

  lshw
  

Usage: lshw -c video #This will provide information about video hardware.

Note

You need to be super-user to run this command and get all information about hardware.

• Show information about particular module:

  modinfo <driver_name>
  

  Usage : modinfo nvidia #This will provide information about nvidia driver

Swap

• More swap with a swap file:

  dd if=/dev/zero of=/swapfile bs=1024 count=65536 #Create 64MB swap file on your root partition
  mkswap /swapfile 65536          #convert file to swap file
  sync
  swapon /swapfile        #add swapfile to your swapspace
  

Memory

• Check memory status of:

  head -2 /proc/meminfo
  

  Usage: provide Available and Used memory of current state of machine

• View the different caches and their sizes:

  sudo head -2 /proc/slabinfo; sudo cat /proc/slabinfo | egrep dentry\|inode
  

  Courtesy: http://linuxaria.com/howto/linux-memory-management

wget

• Download list of files using wget:

  cat <file_containing_url> | xargs wget -c
  

  Usage : cat urlist.txt | xargs wget -c #download content of url for urlist.txt