Linux Administration: Ubuntu Linux Tutorial for Beginners

Pre-requisites

Ubuntu Server Version (or Desktop)

What we will do?

Learn Basic Commands.
Learn User Administration
Learn File Permission Commands.
Learn Networking Commands.
Learn Devil’s Command.

Learn Basic Commands

Once you get connected to the server, you will see a screen as follows.

Before proceeding with the commands, let’s understand what is being displayed on the screen.

Here,

ubuntu is a username usich which you have logged-in into the system.

ip-172-31-43-22 is the hostname  of the system.

$ shows that you are in the normal prompt (non-root user)

# shows that you are in the root user prompt

In our system we have logged-in using a non-root user that’s why we see $ in our terminal

Now let's see the basic command of linux.

See IP Address of the system along with other system network information.

ifconfig

See Linux Version. This will display the version and the flavour of the linux system. The "cat" command will read the "/etc/issue".

cat /etc/issue

See Linux version/favour along with more details.

cat /etc/os-release

See the username using which we have logged-in into the system.

whoami

See the Hostname of the system.

hostname

See System date along with day, time and time zone.

date

See current directory/folder.

pwd

Create a new directory/folder at the current location.

mkdir my-first-directory

Create a new file at the current location.

touch my-first-file

Output

Clear the screen. This will just clear the screen and you can still scroll down to see the previous text.

clear

List files and folders in the present directory.

ls

List files and folders in the present directory with more details about them.

ls -l

Change the directory.

cd my-first-directory/

Go back to the previous directory.

cd -

Output

Open file to write in it.

vim my-first-file

Press “i” to go into “write” mode 
Then write whatever you want
Now press Esc :wq! to save and exit the file

Output

Read the file without opening it for writing.

cat my-first-file

Exit the file without saving it.

vim my-first-file

Write in it
Now press Esc :q! to exit the file without saving.

Output

Now, read the file using cat command we saw in the above step.

cat my-first-file

See the directory structure Linux Server has.

Switch the directory to / using cd command and list the files using ls -l command.

cd /
ls -l

Output

These were a few of the basic commands to perform normal operations in the server.

Before proceeding further with little advance commands, let’s understand the “Common Top Level Directories” in short.

/	The directory called “root.” It is the starting point for the file system hierarchy. Note that this is not related to the root, or superuser, account.
/bin	Binaries and other executable programs.
/etc	System configuration files.
/home	Home directories.
/opt	Optional or third party software.
/tmp	Temporary space, typically cleared on reboot.
/usr	User related programs.
/var	Variable data, most notably log files.

Learn User Administration Commands

In this section we will see simple commands to create a new user and delete it.

To deal with user administration commands, we need to have 'sudo' permission. 'sudo' needs to be appended before executing any administration command.

Add a new user.

sudo useradd rahul

Delete the user.

sudo userdel rahul

Learn File Permission Commands.

In this section we will see how file/directory permissions/ownership can be changed.

First we will see how to deal with file permission commands.

There is no need to have 'sudo' permission unless the files/directories belong to other user.

First we will create a file using touch command, then add text in it and then change its permissions. You can try yourself for directory.

Create a file.

touch test-permissions.txt

List the current directory.

ls -lt

Output

Before playing with file/folder permissions, let's understand it first. When you list the files/directories using 'ls -l', you will see some information as seen in the above screenshot.

The first character can be either ‘-‘, which means it is a file or ‘d’, which means it is a folder/directory.
The next nine characters (rw-rw-r--) show the security. Refer the following screenshot to understand the meaning of these(-rw-rw-r--) characters

We will see Numeric Code in Linux to change file permission which is the easiest way.

0 = No Permission
1 = Execute
2 = Write
4 = Read

We need to add the numbers depending on the level of permission we want to give.

Permission numbers are:

0 = ---
1 = --x
2 = -w-
3 = -wx
4 = r-
5 = r-x
6 = rw-
7 = rwx

For example:

chmod 777 test-permissions.txt will give read, write, and execute permissions to everyone on test-permissions.txt.
chmod 700 test-permissions.txt will give read, write, and execute permissions to the owner of the file only on test-permissions.txt.
chmod 327 test-permissions.txt will give write and execute (3) permission to the owner, w (2) for the group, and read, write, and execute to other users.

Now let's change the permission of "test-permissions.txt" to 000, 077,277,477,200 one by one and see what happens. The rest you can try and see.

Output

Learn Networking Commands.

These commands help in network troubleshooting. You may not have "traceroute" command in the system. If this is the case then the following command can be used to install it.

sudo apt install traceroute

To see the system IP.

ifconfig

Output

To see the route packets take to the network host.

traceroute google.com

Output

To see the connection on a particular port.

telnet localhost 22

Output

To review each of our network connections and open sockets.

netstat -tulpn

Output

Learn Devil’s Command.

"rm" command is also called as a devil's command in linux. It is a remove command, used to delete files and folders.

Since there is no Trash/Bin in server version, rm needs to be used very carefully. Once deleting the file makes it delete permanently hence rm is known as Devil's command. Now let's see its usage to delete files and folders.

Delete a file.