Linux system that works

Linux Guide/How Linux Works

Contents

The Linux Philosophy [ edit | edit source ]

Linux is built with a certain set of unifying principles in mind. Understanding these principles is very helpful in understanding how the system works as a whole. They are known as the «Linux Way», which is derived from the philosophy behind the UNIX system.

The Linux Way can be summarized as:

• Use programs that do only one task, but do it well.
• To accomplish complex tasks, use several programs linked together.
• Store information in human-readable plain text files whenever it is possible.
• There is no «one true way» to do anything.
• Prefer commandline tools over graphical tools.

Most traits of Linux are a consequence of these principles. In accordance with them, a Linux system is built out of small, replaceable components. We will examine the most important of them in more detail. Those are: the boot loader, the kernel, the shell, the X window server, the window manager and the desktop environment. After that, we will have a look at the file system in Linux. Finally, we will discuss the security of a computer running Linux.

Core components of a Linux system [ edit | edit source ]

Boot loader [ edit | edit source ]

This is the part of the system that is executed first. When you have only one operating system installed, it simply loads the kernel (see below). If you happen to have multiple operating systems or multiple versions of the Linux kernel installed, it allows you to choose which one you want to start. The most popular bootloaders are GRUB (GRand Unified Bootloader) and Lilo (LInux LOader). Most users don’t need to care about the boot loader, because it is installed and configured automatically. Actually, the boot Loader creates the boot sequence that the Linux Kernel requires, loading the kernel and some device drivers required for early boot process into memory (as part of so-called «initramfs»), and starting the kernel.

Kernel [ edit | edit source ]

The kernel is the central component of the system that communicates directly with the hardware. In fact, the name «Linux» properly refers to a particular kind of this piece of software. It allows programs to ignore the differences between various computers. The kernel allocates system resources like memory, processor time, hard disk space and external devices to the programs running on the computer. It separates each program from the others, so that when one of them encounters an error, others are not affected. Most users don’t need to worry about the kernel in day-to-day use, but certain software or hardware will require or perform better with certain kernel versions.

Daemons [ edit | edit source ]

In a typical Linux system there are various services running as processes in the background, taking care of things like configuring your network connection, responding to connected USB devices, managing user logins, managing filesystems, etc. They are often called «daemons», because they are running silently and are mostly invisible to the user.

One of these «daemons», started by the kernel after it finishes booting itself, is called init , and its role is to start the rest of the system, including all other «daemons» and graphical sessions.

Different Linux distributions use different init systems. The traditional init system used since the old Unix era, is Sys V init (referring to the System V Unix). But recently many distributions have switched to more modern init systems, such as systemd .

Shell [ edit | edit source ]

The shell, sometimes also called «command line», implements a textual interface that allows you to run programs and control the system by entering commands from the keyboard. Without a shell (or something that can replace it, like a desktop environment) making your system actually do something would be difficult. The shell is just a program; there are several different shells for Linux, each of which offering somewhat different features. Most Linux systems use the Bourne Again Shell (Bash). Linux shells support multitasking (running several programs at once).

X Window Server [ edit | edit source ]

The X window server is a graphical replacement for the command shell. It is responsible for drawing graphics and processing input from the keyboard, mouse, tablets and other devices. The X server is network transparent; that is, it allows you to work in a graphical environment both on your own computer and on a remote computer to which you connect across a network. The X server that is most used today is X.Org. Most graphical programs need only the X server to run, so they can be used under any window manager and desktop environment.

Window Manager [ edit | edit source ]

The window manager is a program that communicates with the X server. Its task is managing windows. It is responsible for drawing the window borders, bringing a window to the front when you click it, moving it on the screen and hiding it when you minimize its program. Examples of popular window managers are:

• Metacity — GNOME Desktop Environment window manager
• KWin — KDE window manager
• Xfwm — Xfce window manager, a lightweight manager designed to consume as little resources as possible without compromising usability
• Compiz Fusion — an advanced window manager with lots of eye candy like customizable window animations, multiple desktops placed on a cube that you can rotate with your mouse, transparent window borders, wobbling windows while dragging them, etc.

Desktop Environment [ edit | edit source ]

Desktop environments such as GNOME Desktop Environment, KDE and Xfce are collections of programs designed to present a consistent user interface for most common tasks. They are what most people mean when they say «operating system» even though they are only a piece of the whole operating system. Multiple desktop environments can coexist on the same machine. They can be easily installed and after installation the user will be given a way to select which DE to start the session with.

File System [ edit | edit source ]

There are several file systems that Linux-based distributions use. They are BTRFS, EXT3/4, VFS, NILFS, and SquashFS.

The hard drive of your computer has a rather simple interface. It only accepts commands like «read block no. 550923 and put it in memory address 0x0021A400». Suppose you are editing a piece of text and want to save it on the disk. Using block numbers (addresses) to identify pieces of data, like your text, is awkward: not only would you have to tell your program where to save the file using raw block numbers, you would have to make sure that these blocks aren’t already being used for family photos, your music collection, or even your system’s kernel. To solve this, files were introduced. A file is an area of the disk which stores data and which has a name (like «example.txt»). Files are organized in collections called directories. Directories can contain other directories, in a tree-like structure. Each file can be uniquely identified by a «path,» which describes its place in the directory hierarchy. For the remainder of this section, it will be assumed that you are familiar with files, directories, and paths.

In Linux, the top-level directory is called the root directory. Every file and directory in the system must be a descendant of the root directory. (It is common to talk about directories using the terminology of family relations, like «parent,» «child,» «descendant,» «ancestor,» «sibling,» and so forth.) Names of files and directories can contain all characters except the null character (which is impossible to enter from the keyboard) and the «/» character. An example path would be:

This path refers to a file called «error.log» which is found in a directory called «apache,» which is a subdirectory of a directory called «logs,» which is subdirectory of a directory called «var,» which is a subdirectory of the root directory. The root directory doesn’t have a name like the other; it is just denoted with a «/» character at the beginning of the path.

The root directory usually contains only a small number of subdirectories. The most important are:

• bin — programs needed to perform basic tasks, i.e. change a directory or copy a file
• dev — special files that represent hardware devices
• etc — configuration files
• home — contains private directories of users
• media or mnt — Mount point for external drives connected to this computer, i.e. CDs or USB keys
• tmp — temporary files
• usr — programs installed on the computer
• var — variable data produced by programs, like error logs

Devices as files [ edit | edit source ]

Just as files can be written to and read, devices in the computer system may send and receive data. Because of this, Linux represents the devices connected to the system as files in the /dev directory. These files can not be renamed or moved (they are not stored on any disk). This approach greatly simplifies application programming. If you want to send something to another computer through a serial port, you don’t even need another program — you simply write to the file /dev/ttyS0, which represents a serial port. In the same manner the file representing the sound card (/dev/dsp) can be read to capture the sound from an attached microphone, or written to in order to produce sound through the speakers.

Where are the drive letters? [ edit | edit source ]

If you have used Windows, you might be surprised that there are no drive letters in Linux. The root directory represents the drive on which the system is installed (C: in Windows). Other drives can be «mounted» or «unmounted» in any directory (preferably, an empty one) in the file system. By mounting a disk, you attach the root directory of this disk to a directory in the file system. After that, you can access the disk like it were a part of your system disk. For example: if you have a disk that contains a directory text, which in turn contains a file called linux-intro.tex and you mount this drive in the directory /media/usbkey, you can access the file linux-intro.tex through the path /media/usbkey/text/linux-intro.tex.

In most Linux distributions, USB keys and CDs are automatically mounted when they are inserted or attached, and the default mount directory is a subdirectory of /media or /mnt. For example, your first CD-ROM drive might be mounted at /media/cdrom0, while the contents of a USB key might be accessible through /media/usb0. You may manually change the mount directory, but you will have to learn two shell commands and know the device file that represents your drive to do that (the one we talked about in the preceding section — disks also get their file representation in the /dev directory). We will cover this subject later.

Users [ edit | edit source ]

The user is a metaphor for somebody or something interacting with the system. Users are identified by a user name and a password. Internally, each user has a unique number assigned, which is called a user ID, or UID for short. You only need to know your UID in some rare situations. Users can additionally be organized in groups. There is one special user in all Linux systems, which has the user name «root» and UID 0. It is also called the superuser. The superuser can do anything and is not controlled in any way by the security mechanisms. Having such a user account is very useful for administrative tasks and configuring the system. In some distributions (like Ubuntu) direct access to the root account is disabled and other mechanisms are used instead.

If you have more than one user account on a Linux system, you do not need to log out and back again to switch impersonations. There are special shell commands that allow you to access files and execute programs as other users, provided you know their user names and passwords. Thanks to this mechanism, you can spend most of the time as a user with low-privileges and switch to a higher-privileged account only if you need to.

The advantage of running as a non-privileged user is that any mistakes you happen to make are very unlikely to damage the system. System-critical components can only be altered by the root user.

File permissions [ edit | edit source ]

Users exist to control the extent to which people and programs using the system can control it. This is accomplished by a system of file permissions. Each file belongs to one of the users — that is, each file has an owner. Additionally, a file can be assigned to a group of users, but the owner must be a member of that group. Each file has three kinds of permissions: read, write and execute. These permissions can be assigned to three kinds of owner relations: owner, group and other. Other includes all users who are not the owner of the file and do not belong to the group which owns the file. Only the file owner or the superuser (root) can change the permissions or ownership of a file.

This system allows precise control over who can do what on a given computer. Users can be prevented from modifying system files by removing the «write» permission from them, or from executing certain commands by removing the «execute» permission. Notice that users may be allowed to execute programs but not alter them. This is very important, since most Linux systems include a compiler that allows you to create your own programs.

File permissions are usually given as three octal digits (each from 0 to 7). The digits represent the permissions for, respectively, owner, group and other users. Each digit is the sum of permission codes: 1 for execute, 2 for write and 4 for read. For example, «755» allows everyone to read or execute the file, but only its owner can write it. «400» allows the owner to read the file, and no one else is allowed to do anything. «540» allows the owner to read or execute the file, group members to only read the file and other users to do nothing.

chmod (change mode), chown (change owner), and chgrp (change group) are used to change file permissions.

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What is Linux?

From smartphones to cars, supercomputers and home appliances, home desktops to enterprise servers, the Linux operating system is everywhere.

Linux has been around since the mid-1990s and has since reached a user-base that spans the globe. Linux is actually everywhere: It?s in your phones, your thermostats, in your cars, refrigerators, Roku devices, and televisions. It also runs most of the Internet, all of the world’s top 500 supercomputers, and the world’s stock exchanges.

But besides being the platform of choice to run desktops, servers, and embedded systems across the globe, Linux is one of the most reliable, secure and worry-free operating systems available.

Here is all the information you need to get up to speed on the Linux platform.

What is Linux?

Just like Windows, iOS, and Mac OS, Linux is an operating system. In fact, one of the most popular platforms on the planet, Android, is powered by the Linux operating system. An operating system is software that manages all of the hardware resources associated with your desktop or laptop. To put it simply, the operating system manages the communication between your software and your hardware. Without the operating system (OS), the software wouldn?t function.

The Linux operating system comprises several different pieces:

1. Bootloader – The software that manages the boot process of your computer. For most users, this will simply be a splash screen that pops up and eventually goes away to boot into the operating system.
2. Kernel – This is the one piece of the whole that is actually called ?Linux?. The kernel is the core of the system and manages the CPU, memory, and peripheral devices. The kernel is the lowest level of the OS.
3. Init system – This is a sub-system that bootstraps the user space and is charged with controlling daemons. One of the most widely used init systems is systemd? which also happens to be one of the most controversial. It is the init system that manages the boot process, once the initial booting is handed over from the bootloader (i.e., GRUB or GRand Unified Bootloader).
4. Daemons – These are background services (printing, sound, scheduling, etc.) that either start up during boot or after you log into the desktop.
5. Graphical server – This is the sub-system that displays the graphics on your monitor. It is commonly referred to as the X server or just X.
6. Desktop environment – This is the piece that the users actually interact with. There are many desktop environments to choose from (GNOME, Cinnamon, Mate, Pantheon, Enlightenment, KDE, Xfce, etc.). Each desktop environment includes built-in applications (such as file managers, configuration tools, web browsers, and games).
7. Applications – Desktop environments do not offer the full array of apps. Just like Windows and macOS, Linux offers thousands upon thousands of high-quality software titles that can be easily found and installed. Most modern Linux distributions (more on this below) include App Store-like tools that centralize and simplify application installation. For example, Ubuntu Linux has the Ubuntu Software Center (a rebrand of GNOME Software? Figure 1) which allows you to quickly search among the thousands of apps and install them from one centralized location.

Why use Linux?

This is the one question that most people ask. Why bother learning a completely different computing environment, when the operating system that ships with most desktops, laptops, and servers works just fine?

To answer that question, I would pose another question. Does that operating system you?re currently using really work ?just fine?? Or, do you find yourself battling obstacles like viruses, malware, slow downs, crashes, costly repairs, and licensing fees?
If you struggle with the above, Linux might be the perfect platform for you. Linux has evolved into one of the most reliable computer ecosystems on the planet. Combine that reliability with zero cost of entry and you have the perfect solution for a desktop platform.

That’s right, zero cost of entry… as in free. You can install Linux on as many computers as you like without paying a cent for software or server licensing.

Let’s take a look at the cost of a Linux server in comparison to Windows Server 2016. The price of the Windows Server 2016 Standard edition is $882.00 USD (purchased directly from Microsoft). That doesn’t include Client Access License (CALs) and licenses for other software you may need to run (such as a database, a web server, mail server, etc.). For example, a single user CAL, for Windows Server 2016, costs $38.00. If you need to add 10 users, for example, that’s $388.00 more dollars for server software licensing. With the Linux server, it?s all free and easy to install. In fact, installing a full-blown web server (that includes a database server), is just a few clicks or commands away (take a look at ?Easy LAMP Server Installation? to get an idea how simple it can be).

If zero cost isn’t enough to win you over? what about having an operating system that will work, trouble free, for as long as you use it? I’ve used Linux for nearly 20 years (as both a desktop and server platform) and have not had any issues with ransomware, malware, or viruses. Linux is generally far less vulnerable to such attacks. As for server reboots, they’re only necessary if the kernel is updated. It is not out of the ordinary for a Linux server to go years without being rebooted. If you follow the regular recommended updates, stability and dependability are practically assured.

Open source

Linux is also distributed under an open source license. Open source follows these key tenants:

• The freedom to run the program, for any purpose.
• The freedom to study how the program works, and change it to make it do what you wish.
• The freedom to redistribute copies so you can help your neighbor.
• The freedom to distribute copies of your modified versions to others.

These points are crucial to understanding the community that works together to create the Linux platform. Without a doubt, Linux is an operating system that is ?by the people, for the people?. These tenants are also a main factor in why many people choose Linux. It?s about freedom and freedom of use and freedom of choice.

What is a “distribution?”

Linux has a number of different versions to suit any type of user. From new users to hard-core users, you’ll find a “flavor” of Linux to match your needs. These versions are called distributions (or, in the short form, “distros”). Nearly every distribution of Linux can be downloaded for free, burned onto disk (or USB thumb drive), and installed (on as many machines as you like).

Popular Linux distributions include:

• LINUX MINT
• MANJARO
• DEBIAN
• UBUNTU
• ANTERGOS
• SOLUS
• FEDORA
• ELEMENTARY OS
• OPENSUSE

Each distribution has a different take on the desktop. Some opt for very modern user interfaces (such as GNOME and Elementary OS’s Pantheon), whereas others stick with a more traditional desktop environment (openSUSE uses KDE).

You can check out the top 100 distributions on the Distrowatch.

And don’t think the server has been left behind. For this arena, you can turn to:

• Red Hat Enterprise Linux
• Ubuntu Server
• Centos
• SUSE Enterprise Linux

Some of the above server distributions are free (such as Ubuntu Server and CentOS) and some have an associated price (such as Red Hat Enterprise Linux and SUSE Enterprise Linux). Those with an associated price also include support.

Which distribution is right for you?

Which distribution you use will depend on the answer to three simple questions:

• How skilled of a computer user are you?
• Do you prefer a modern or a standard desktop interface?
• Server or desktop?

If your computer skills are fairly basic, you’ll want to stick with a newbie-friendly distribution such as Linux Mint, Ubuntu (Figure 3), Elementary OS or Deepin. If your skill set extends into the above-average range, you could go with a distribution like Debian or Fedora. If, however, you’ve pretty much mastered the craft of computer and system administration, use a distribution like Gentoo. If you really want a challenge, you can build your very own Linux distribution, with the help of Linux From Scratch.

If you’re looking for a server-only distribution, you will also want to decide if you need a desktop interface, or if you want to do this via command-line only. The Ubuntu Server does not install a GUI interface. This means two things your server won’t be bogged down loading graphics and you’ll need to have a solid understanding of the Linux command line. However, you can install a GUI package on top of the Ubuntu Server with a single command like sudo apt-get install ubuntu-desktop. System administrators will also want to view a distribution with regards to features. Do you want a server-specific distribution that will offer you, out of the box, everything you need for your server? If so, CentOS might be the best choice. Or, do you want to take a desktop distribution and add the pieces as you need them? If so, Debian or Ubuntu Linux might serve you well.

Installing Linux

For many people, the idea of installing an operating system might seem like a very daunting task. Believe it or not, Linux offers one of the easiest installations of all operating systems. In fact, most versions of Linux offer what is called a Live distribution ? which means you run the operating system from either a CD/DVD or USB flash drive without making any changes to your hard drive. You get the full functionality without having to commit to the installation. Once you’ve tried it out, and decided you wanted to use it, you simply double-click the “Install” icon and walk through the simple installation wizard.

Typically, the installation wizards walk you through the process with the following steps (We’ll illustrate the installation of Ubuntu Linux):

• Preparation: Make sure your machine meets the requirements for installation. This also may ask you if you want to install third-party software (such as plugins for MP3 playback, video codecs, and more).
• Wireless setup (if necessary): If you are using a laptop (or machine with wireless), you’ll need to connect to the network, in order to download third-party software and updates.
• Hard drive allocation (Figure 4): This step allows you to select how you want the operating system to be installed. Are you going to install Linux alongside another operating system (called “dual booting”), use the entire hard drive, upgrade an existing Linux installation, or install over an existing version of Linux.
• Location: Select your location from the map.
• Keyboard layout: Select the keyboard for your system.
• User setup: Set up your username and password.

That’s it. Once the system has completed the installation, reboot and you’re ready to go. For a more in-depth guide to installing Linux, take a look at “How to Install and Try Linux the Absolutely Easiest and Safest Way” or download the Linux Foundation’s PDF guide for Linux installation.

Installing software on Linux

Just as the operating system itself is easy to install, so too are applications. Most modern Linux distributions include what most would consider an app store. This is a centralized location where software can be searched and installed. Ubuntu Linux (and many other distributions) rely on GNOME Software, Elementary OS has the AppCenter, Deepin has the Deepin Software Center, openSUSE has their AppStore, and some distributions rely on Synaptic.

Regardless of the name, each of these tools do the same thing? a central place to search for and install Linux software. Of course, these pieces of software depend upon the presence of a GUI. For GUI-less servers, you will have to depend upon the command-line interface for installation.

Let’s look at two different tools to illustrate how easy even the command line installation can be. Our examples are for Debian-based distributions and Fedora-based distributions. The Debian-based distros will use the apt-get tool for installing software and Fedora-based distros will require the use of the yum tool. Both work very similarly. We’ll illustrate using the apt-get command. Let’s say you want to install the wget tool (which is a handy tool used to download files from the command line). To install this using apt-get, the command would like like this:

The sudo command is added because you need super user privileges in order to install software. Similarly, to install the same software on a Fedora-based distribution, you would first su to the super user (literally issue the command su and enter the root password), and issue this command:

That’s all there is to installing software on a Linux machine. It’s not nearly as challenging as you might think. Still in doubt? Recall the Easy Lamp Server Installation from earlier? With a single command:

You can install a complete LAMP (Linux Apache MySQL PHP) server on either a server or desktop distribution. It really is that easy.

More resources

If you’re looking for one of the most reliable, secure, and dependable platforms for both the desktop and the server, look no further than one of the many Linux distributions. With Linux you can assure your desktops will be free of trouble, your servers up, and your support requests minimal.

For more information to help guide you through your lifetime with Linux, check out the following resources:

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