Linux®

Linux® is an open source operating system (OS). An operating system is the software that directly manages a system’s hardware and resources, like CPU, memory, and storage. The OS sits between applications and hardware and makes the connections between all of your software and the physical resources that do the work.

How does Linux work?
Linux was designed to be similar to UNIX, but has evolved to run on a wide variety of hardware from phones to supercomputers. Every Linux-based OS involves the Linux kernel—which manages hardware resources—and a set of software packages that make up the rest of the operating system.
The OS includes some common core components, like the GNU tools, among others. These tools give the user a way to manage the resources provided by the kernel, install additional software, configure performance and security settings, and more. All of these tools bundled together make up the functional operating system. Because Linux is an open source OS, combinations of software can vary between Linux distributions.

What's a command line?
The command line is your direct access to a computer. It's where you ask software to perform hardware actions that point-and-click graphical user interfaces (GUIs) simply can't ask.

Command lines are available on many operating systems—proprietary or open source. But it’s usually associated with Linux, because both command lines and open source software, together, give users unrestricted access to their computer.

Here some of the linux commands and functionality:

pwd command

Use the pwd command to find out the path of the current working directory (folder) you’re in. The command will return an absolute (full) path, which is basically a path of all the directories that starts with a forward slash (/). An example of an absolute path is /home/username.

cd command

To navigate through the Linux files and directories, use the cd command. It requires either the full path or the name of the directory, depending on the current working directory that you’re in.

ls command

The ls command is used to view the contents of a directory. By default, this command will display the contents of your current working directory.
If you want to see the content of other directories, type ls and then the directory’s path.

cat command

cat (short for concatenate) is one of the most frequently used commands in Linux. It is used to list the contents of a file on the standard output (sdout). To run this command, type cat followed by the file’s name and its extension. For instance: cat file.txt.

cp command

Use the cp command to copy files from the current directory to a different directory. For instance, the command cp scenery.jpg /home/username/Pictures would create a copy of scenery.jpg (from your current directory) into the Pictures directory.

 mv command

The primary use of the mv command is to move files, although it can also be used to rename files.
The arguments in mv are similar to the cp command. You need to type mv, the file’s name, and the destination’s directory. For example: mv file.txt /home/username/Documents.
To rename files, the Linux command is mv oldname.ext newname.ext

mkdir command

Use mkdir command to make a new directory — if you type mkdir Music it will create a directory called Music.

 rm command

The rm command is used to delete directories and the contents within them. If you only want to delete the directory — as an alternative to rmdir — use rm -r.
Note: Be very careful with this command and double-check which directory you are in. This will delete everything and there is no undo.

touch command

The touch command allows you to create a blank new file through the Linux command line. As an example, enter touch /home/username/Documents/Web.html to create an HTML file entitled Web under the Documents directory.

 find command

Similar to the locate command, using find also searches for files and directories. The difference is, you use the find command to locate files within a given directory.
As an example, find /home/ -name notes.txt command will search for a file called notes.txt within the home directory and its subdirectories.

 df command

Use df command to get a report on the system’s disk space usage, shown in percentage and KBs. If you want to see the report in megabytes, type df -m.

 du command

If you want to check how much space a file or a directory takes, the du (Disk Usage) command is the answer. However, the disk usage summary will show disk block numbers instead of the usual size format. If you want to see it in bytes, kilobytes, and megabytes, add the -h argument to the command line

 chmod command

chmod is another Linux command, used to change the read, write, and execute permissions of files and directories. As this command is rather complicated, you can read the full tutorial in order to execute it properly.

chown command

In Linux, all files are owned by a specific user. The chown command enables you to change or transfer the ownership of a file to the specified username. For instance, chown linuxuser2 file.ext will make linuxuser2 as the owner of the file.ext.

 kill command

If you have an unresponsive program, you can terminate it manually by using the kill command. It will send a certain signal to the misbehaving app and instructs the app to terminate itself.
After knowing what signal you want to use and the PID of the program, enter the following syntax:

 ping command

Use the ping command to check your connectivity status to a server. For example, by simply entering ping google.com, the command will check whether you’re able to connect to Google and also measure the response time.

whoami command 

Is used both in Unix Operating System and as well as in Windows Operating System. It is basically the concatenation of the strings “who”,”am”,”i” as whoami. It displays the username of the current user when this command is invoked.

whereis command

whereis command is used to find the location of source/binary file of a command and manuals sections for a specified file in Linux system.

grep command 

Grep is a Linux / Unix command-line tool used to search for a string of characters in a specified file. The text search pattern is called a regular expression. When it finds a match, it prints the line with the result. The grep command is handy when searching through large log files.

df-h command 

Using ' -h ' parameter with (df -h) will show the file system disk space statistics in “human readable” format, means it gives the details in bytes, megabytes, and gigabyte. This article explains a way to get the full information of Linux disk space usage with the help of 'df' command with their practical examples.

du-h command

Using “-h” option with “du” command provides results in “Human Readable Format“. Means you can see sizes in Bytes, Kilobytes, Megabytes, Gigabytes etc. 3. To get the summary of a grand total disk usage size of an directory use the option “-s” as follows.

top command 

Is used to show the Linux processes. It provides a dynamic real-time view of the running system. Usually, this command shows the summary information of the system and the list of processes or threads which are currently managed by the Linux Kernel.

exit command

In linux is used to exit the shell where it is currently running. It takes one more parameter as [N] and exits the shell with a return of status N. If n is not provided, then it simply returns the status of last command that is executed. After pressing enter, the terminal will simply close.

cowsay command

Is an udderly fantastic utility that takes text and outputs it as the spoken text of an ASCII-art bovine. You'll likely find cowsay packaged in your default repositories, and perhaps even already installed. Cowsay ships with few variations, called cow files, that can usually be found in /usr/share/cowsay. To see the cow file options available on your system, use -l flag after cowsay. Then, use the -f flag to try one out. $ cowsay -f dragon "Run for cover, I feel a sneeze coming on."

apt command

Is a command-line utility for installing, updating, removing, and otherwise managing deb packages on Ubuntu, Debian, and related Linux distributions. It combines the most frequently used commands from the apt-get and apt-cache tools with different default values of some options. apt is designed for interactive use.

vim command

Is a powerful text editor used in CLI (command line interface). Linux uses a lot of configuration files, you'll often need to edit them and vim is a great tool to do so. Alternatives to vim are the command-line editor's nano and joe. The vim edit will show up in the terminal window.

nmap command 

Nmap, or Network Mapper, is an open source Linux command line tool for network exploration and security auditing. With Nmap, server administrators can quickly reveal hosts and services, search for security issues, and scan for open ports.

more command

The Linux more command lets you view text files or other output in a scrollable manner. It displays the text one screenful at a time, and lets you scroll backwards and forwards through the text, and even lets you search the text.