Basic Linux Commands

👉🏻 date command

date command prints the current date time.

$ date

👉🏻 cal command

cal command is used to display a calendar in your shell, by default it will display the current month

$ cal

👉🏻 Clear terminal

$ clear

👉🏻 Exit terminal

$ exit

👉🏻 whoami command

whoami command will tell you which user account you are using in this system.

$ whoami

👉🏻 Show current uptime.

$ uptime

👉🏻 CPU information.

$ cat /proc/cpuinfo

👉🏻  Show disk usage

$ df

👉🏻 Show directory space usage

$ du

👉🏻  Show memory and swap usage

$ free

👉🏻 Install Package

$ pkg install package_name

 

👉🏻 Update Single Package

$ pkg update package_name

👉🏻 Update all packages

$ pkg update && upgrade

👉🏻 id command

id prints real user id, and various other details related to the account.

$ id

👉🏻 pwd command

pwd command, short for print working directory, will help you to find out the absolute path of the current directory.

$ pwd

👉🏻 cd command

The next command we will learn is cd, short for change directory. This command will help you to change your current

directory. We will move to /tmp directory in our example.

$ cd /tmp

👉🏻. directory and .. directory

. and .. has special meaning in the Linux. . means the current directory and .. means the parent directory. We can use these in various situations for daily activities.

$ cd ..

👉🏻 ls command

We use ls command to list the files and directories inside any given directory. If you use ls command without any argument, then it will work on the current directory. We will see few examples of the command below.

$ ls

👉🏻 mkdir command

We can create new directories using mkdir command. For our example we will create a code directory inside our home

directory.

$ mkdir foldername

We can also create nested directories in a single command using the -p option.:

$ mkdir -p dir1/dir2/dir3

👉🏻 rm command

rm command is used to remove a file, or directory. The -r option is being used to remove in a recursive way. With -f you force the removal, ignoring errors and never prompt. You can chain the flags, so instead of rm -r -f you can as well type rm -rf. But, always double check before you use rm -rf command, if you by mistake give this command in

your home directory, or any other important directory, it will not ask to confirm, but it will delete everything there. So, please be careful and read twice before pressing enter key.

$ rm -rf dir1/dir2/dir3

👉🏻 Delete file

$ rm filename

👉🏻 Delete directory

$ rm -r dir

👉🏻 Force remove file

$ rm -f file

👉🏻 Force remove 

$ rm -rf dir

👉🏻 Create or update file

$ touch filename

👉🏻 Places standard input into file.

$ cat > file 

👉🏻 Copying a file using cp command

We use the cp command to copy a file in the Linux shell. To copy a folder with its contents recursively use the cp command with the -r flag. We use the cp file_to_copy new_location format. In the example below, we are copying the

hello.txt to hello2.txt.

$ cp hello.txt hello2.txt

👉🏻 Renaming or moving a file

The mv command is used to rename or move a file or directory. In the following example, the file hello.txt is re-named to nothello.txt

$ mv hello.txt nothello.txt

👉🏻 Give Permission 

Change the permissions of file

to octal, which can be found separately for user,

group, and world by adding:

● 4 – read (r)

● 2 – write (w)

● 1 – execute (x)

👉🏻 Permissions read, write, execute for all

$ chmod 777

👉🏻 wc command

wc, short for word count, is an useful command which can help us to count newlines, words and bytes of a file.

$ wc -l hello.txt

3 hello.txt

$ wc -w hello.txt

17 hello.txt

The -l flag finds the number of lines in a file, -w counts the number of words in the file.

👉🏻 echo command

echo command echoes any given string to the display.

$ echo "Hello"

👉🏻 Moving around in the command line

There are key shortcuts available in Bash which will help you to move around faster. They are by the way very similar to the standard emacs keybindings, a number of key combinations that you will discover in many places and therefore

are very handy to memorize and internalize. The following table is a good starting point.

Ctrl + A : Move to the beginning of the line

Ctrl + E : Move to the end of the line

Alt + B : Move to the previous word

Alt + F : Move to the next word

Ctrl + U : Erase to the beginning of the line

Ctrl + K : Erase to the end of the line

Ctrl + W : Erase the previous word

Ctrl + P : Browse previously entered commands

Ctrl + R : Reverse search for previously entered command

👉🏻 man pages

man shows the system’s manual pages. This is the command we use to view the help document (manual page) for any command. The man pages are organized based on sections, and if the same command is found in many different

sections, only the first one is shown.

The general syntax is man section command. Example

$ man 7 signal.

You can know about different sections below. Press q to quit the program.

👉🏻 ping command

ping is simple way to find if you are connected to Internet or not. We can also ping any particular computer to find if the computer is connected to the network or not. Press Ctrl+c to stop the loop.

$ ping google.com

👉🏻 Sort files by size

You can use -S or –sort=size option to the ls command.

$ ls -lSh

You can reverse the sorting with passing -r option.

👉🏻 chmod command

chmod is the command which changes the file mode bits. Through chmod command one can alter the access permissions (i.e to permissions to read, write and execute) to file system objects (i.e files and directories). If we look at the command closely chmod is the abbreviation of change mode. A few examples are given below.

$ chmod 000 myfile.txt

$ cat myfile.txt

cat myfile.txt: Permission denied

$ chmod 600 myfile.txt

In the first line, we created a new file called myfile.txt using the echo command (we redirected the output of echo into the file). Using the chmod 000 myfile.txt command, we removed the read/write permissions of the file, and as you can see in the next line, even the owner of the file cannot read it. Setting the mode to 600 brings back read/write capability to the owner of that particular file.

The executable permission bit is required for directory access, and also for any file you want to execute.

👉🏻 How to view all running processes?

The following command shows all the processes from your computer.

$ ps aux

👉🏻 How to find a particular process?

Let’s say, I want to know the process id of change the permissions of file

to octal, which ca

group, and world by adding:n be found separately for user, Firefox browser in my system. I can use the following command to find

that information.

$ ps aux grep firefox

👉🏻 How to kill/stop a particular process?

We can kill/stop any process using the kill command. We found out, in the last example, that the id of the Firefox process in my computer is 26752, we can use that id to kill it.

$ kill 26752

If there is no error message, you’ll find that Firefox has disappeared.

👉🏻 top command

top is a very useful command while using a Linux system. It’s a quick way to know about all the running processes in the system, and their related status about CPU and memory usage in general. To get out of top, press CTRL + C.

$ top

👉🏻 htop tool

htop is a modern version of the top tool. It has many more features, interactiveness being the biggest amongst them.

htop does not come by default in most of the Linux installations, which means you will have to install it using the

system’s package management tool.

$ pkg install htop

$ htop