Linux and the boot process

Here are a few online resources which are useful for understanding what Linux, Unix and Open Source Software really are.

• History of Unix, Linux, and Open Source / Free Software by David Wheeler. It is easy to think that Linux is the same thing as Unix but it’s not.
• What is a Linux distribution?. Linux is a kernel. To be useful, it needs to be bundled with hundreds of system and user applications. The bundle is then called a distribution and myriads exist e.g. RedHat, CentOS, Debian and Ubuntu. Why?
• Open Source Definition by the Open Source Initiative. It is equally easy to think that Open Source Software should always be free (for example). But things are much subtler than that. For example, Red Hat Linux needs to be bought but is still open source…
• Finally, The Cathedral and the Bazaar by Eric Raymond. How can software which is developed by hundreds of developers distributed over the whole planet and who are doing it for free can possibly create Linux, an operating system which is arguably better than most commercial operating systems?

Linux is a powerful operating system which provides both text and graphical interfaces. A system administrator must be comfortable with both environments.

The Linux command line

Linux system administrators need to master the Linux command line as this is, arguably, the most efficient and powerful way to interact with the operating system. Then we will proceed to File and Directory Management.

Boot, Initialisation, Shutdown and Run-levels

When a computer is switched on, the following happens:

• The BIOS does a Power On Self Test
• The BIOS launches a bootloader (generally found in the Master Boot Record of the first hard disk)
• This bootloader (generally Grub) allows the user to choose a Linux kernel…
• … which then boots.

A system administrator should know how to:

• Configure Grub properly so that the Linux kernel can boot properly.
• Configure the Linux boot process itself so that only the needed services and drivers are loaded. This includes knowing about the SysV init process, runlevels and the role of the inittab.

Of course, the system administrator should also know how to reboot and shutdown the computer.