Linux Notes

This post is a compilation of some of the notes I made about Linux commands. I usually come back to it for reference. I think it could be helpful to others as well.


To quickly check if a program is installed on Linux, you can use the command dpkg -s followed by the unique package name for that program. The -s flag in dpkg stands for search which allows you to search for a program on your machine and check if it’s installed.

dpkg -s firefox

Updating packages:

sudo apt-get install <package_name>
sudo apt-get install firefox
sudo apt-get remove gimp

Updating repositories:

sudo apt-get update

Note: Repositories are basically servers which contain sets of packages.


We can use the history command to see the history in the terminal or use ctrl+r shortcut for the same.

Checking the Kernel version:

uname -r // see the kernel version

Copying, moving and removing files:

cp <this file> <to this directory>
cp *.jpg <to this directory> // copy all jpg files

mv <this> <that> // rename file
mv <this> <directory> // move the file to the directory

rm <file> // remove file

User and passwords:

passwd <user> // set new pass

sudo passwd -e <user> // expire user’s password and ask them to set new pass next time they log in

sudo useradd <name> // add user
sudio userdel <name> // remove user


There are three ownership types:

  • u = owner
  • g = group
  • o = all

We can modify file permissions by using the chmod command:

chmod u+x filename // give x permission to owner type
chmod u-x filename // remove x permission from owner type
chmod u+rx filename // give rx permission to owner type

There are three permission types:

  • read (r) = 4
  • write (w) = 2
  • execute (x) = 1

The alternate (and popular) way to write chmod command is chmod 754 <filename>, where:

  • 7 = giving read+write+execute (4+2+1) permission to owner.
  • 5 = giving read+execute (4+1) permission to group.
  • 4 = giving read (4) permission to all.

Other two relevant commands:

sudo chown omkar filename // change owner of the file
sudo chgrp best_group_ever filename // change group of the file


du -h // check disk usage, -h gives info in human readable form
df -h // disk free command, -h gives info in human readable form

fsck /dev/sdb  // file system check command. Warning: If you run fsck on a mounted partition, there's a high chance that it'll damage the file system.


When you start up your computer, the kernel creates a process called a init, which has a PID of one. It starts up other processes that we need to get our computer up and running.

Viewing Processes:

ps -x // snapshot of processes running on the system

Process statuses: R = running, T = stopped, S = interruptible sleep (task is waiting for an event to complete before it resumes).

ps -ef // e flag = all processes (even run by other users), f = full details.
ps -ef | grep Chrome // search for chrome process

Killing a Process:

// SIGINT - Signal Interrupt (example control + c)

kill <PID> // kill a process giving it time to clean up
kill -KILL <PID> // this is SIGKILL cmd, i.e. kill without giving the time to cleanup