Steven Landy - Linux Basics: Linux Guide To Learn Linux Commands And Linux Coding (1HourToStart)

In this guide we are going to work with the command line. Though it may result so unfamiliar at the beginning, you will learn how important is for an aspirant administrator to be knowledgeable of the operations available only through the terminal. The modern practice, even for learners, is going toward this direction with cloud servers that offer operating systems available through the terminal. Amazon AWS is an example of cloud servers where you find a large number of machines free to be explored, just enabling the services, setting up your settings and ready to go with the ISO you prefer.

In this guide we use Linux distribution Ubuntu 18.04. You will be able to operate exclusively through the command line to install excellent tools to monitor services and processes, control users, network management, logs, and more.

One of the most frequent command repeated in the book is cd. This command is used to move from one directory to another, followed then by the directory you want to move to. The path of the directory is separated by / that indicates to specify the name of the folder.

cd desktop/folder1

With the following syntax instead, you are able to go back to a previous path. The two dots refers to the structure and indicate the hierarchy of folders.

cd ..

Permissions

A reminder for the next chapter is the importance of permissions. Taking as an assumption that you can always use the current user in your machine, some operations may not be allowed to all users. Thats why it is important to keep an eye on the user you are working with. Sometimes it is necessary to run commands with sudo in front of the command itself to be able to properly execute an operation.

The Man command

When information about one command is not exhaustive, you may find handful to use the man command. Each command has a man available to show information about the command such as:

man kill

Kill is the command that kills processes. With man you can find out all possible options for this command.

What is the Kernel?

In this guide there are many references about the Kernel. If you have not never heard about this term, you may find interesting to have a full understanding of what it is and how it works.

With Kernel we mean the level that works in cooperation between the software and the hardware and it allows the communication between these two through drivers. Though a variety of distributions, there is always a Kernel for the same purpose.

When any application needs to apply changes to the hardware, it transfers the request to the Kernel which translates this request and communicates directly with the driver to accept or refuse requests.

The Kernel is one of the main components of an operating system that connects to the resources. This is why it also takes care of the management of the resources in an operating system.

The Linux Kernel is monolithic which means that is able to run complex operations applying exactly the concept we talked about earlier in this section. So, it takes care of the resources such as CPU, memory, hard drives, I/O devices, while it manages file systems, drivers, etc

While on one hand this type of kernel is able to work appropriately with more precautions on all tasks because all the requests are handled directly by the kernel, on the other hand, this method require to accept all the requests each time. And this process may result in critical issues, when there is a request that still needs to be approved. Some of the advantages of this communication are the access from software to hardware, simple method to speak with each side, no additional drivers may be required, quick response from both sides. It is also true that there are negative aspects of using a Kernel. For instance, it requires memory, and it is not so much a safe choice.

Where are the files?

The Kernel files in Ubuntu are collected under the folder /boot.

What are deamons?

A specific section of this guide is about how to manage processes, but even in others you always find the term deamons. Processes are instances of programs that run to complete tasks. Processes are managed by the Kernel that gives them an identification number (PID). As we will see the PID is essential to work with processes as well as monitor the activities.

Some specific processes run and complete the requests on background while users are working. An example is the mail server that receives and forwards emails while you are working. These processes are not activated by the user but usually they start on their own when as soon as the operating system is booted. Some famous examples of deamons are httpd , Apache, MySQL that are available while you work on different activities.