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In this video we'll show you some of the things that can go wrong during the boot process. Many boot problems relate to the boot loader, which on Red Hat Enterprise Linux is known a GRUB. GRUB-specific issues are covered in another video. We'll look at other boot problems. Sure, problems can happen with the computer power on process, also known as the power on self test, POST for short, but that's not related to Linux and is therefore not covered on the exam. After you select the stance in GRUB it loads the kernel along with the initial RAM disk as defined in the boot directory. If there are problems with that boot directory you may want to look there. Go into rescue mode and see if something is misspelled, or something silly like that. Once it loads the basic files, it eventually gets to the etc inittab configuration file. So there can be a lot of things that can go wrong there. What happens if some administrator sets your default run level to zero? The system would start and immediately move to shut down. What happens if some joker makes your default run level 6, or even just run level 3. The system would not start the GUI as may be required on your exam. Let's look at some of the other directives. What happens if there's an error here? Your default run level is 3, yet all you see booting are single user mode services. You may have an error like this. What do you think would happen if these getty commands were commented out? Gettys are what start log-in terminals. If these are commented out then there would be no log-in terminals, at least text mode log in-terminals. Other potential boot problems relate to files like etc slash fstab. What if the boot device cited the wrong directory? What would happen if the wrong file system were cited? Mucho trouble. What happens if you see the x window configuration file with a misspelled directive? If you were in run level 5 the system would not start the x window. The x window configuration file, remember, is now xorg dot conf in the etc slash x11 directory. If you followed the instructions from a previous video, I urge you to try out different things with each of these files. Move these files to locations that the boot process wouldn't read, so you have the original file backed up in a different place. Reboot your system and find out what happens. Note how it's not fatal to the boot process if the fstab or the xwindow configuration file is missing. Try to introduce syntax errors into some of these files. There are other possibilities. Take a look at the rc dot sysinit file. What happens if this fellow went missing? Would the host name still work? These are just some examples. Be imaginative. Think like a Red Hat person. Think about errors that can be introduced into the boot process and more. Reboot your system. See what appears on your system. Do that a number of times and you'll be ready for the troubleshooting portion of your exam.