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One key skill associated with the Red Hat exams is rescue mode, which can help you boot an otherwise unbootable system. If you encounter problems during the boot process, and I think it likely you will during the RHCE exam, rescue mode can be a lifesaver. While we described potential boot problems in other videos, an understanding of rescue mode is such an important skill, we dedicate this video to that skill. To boot into rescue mode you'll need the first installation CD. While this process also works from a boot CD or USB key configured with the file shown here, the RHCE exam prep guide explicitly states that RHCEs must know how to use the rescue environment provided by the first installation CD. So it's reasonable to expect that you'll have the first installation CD during your exam. So, let's boot from that CD. Of course, when you boot from that CD you get the starting installation screen. Instead of just starting an installation, we boot into Linux Rescue mode. Note how the system boots with the default kernel and in a moment we'll see some steps that look familiar. They look like an installation step but they quickly diverge into rescue mode. In a moment we'll choose a language followed by a keyboard type. And there it is, in text mode. We choose a language and look at that. On top of the screen we see we're in rescue mode already, well, sort of. We select a keyboard type and while it's not required to set up networking, you should, because there may be missing packages and it'll be handy to have the network installation server available. If you're told to set up a static ip address, don't use dhcp. If you can avoid it, I recommend that you don't configure ip version 6, as that adds time to the rescue process. For the purpose of this video, we'll just use dhcp for ip version 4 support. It detects the first Ethernet card and here we are at the rescue screen. There are three options here. Continue and Read Only are essentially the same thing. Continue mounts in Read Write mode, Read Only mounts in Read Only mode. But if you have problems such as file system errors, I recommend that you try out Skip. It accesses the command line interface without mounting anything, at least mounting any partitions from your Red Hat Enterprise Linux installation. That way you'll be able to run commands like fsck on partitions, which may have errors. Of course, you should already note that you can read what partitions are listed with commands like fdisk dash l. Let's see what happens when select Continue. It searches your hard drive for Red Hat Enterprise Linux Server installations and once the search finds something you'll see the following screen: voil‡. It shows that the system is mounted in subdirectories of the mnt sysimage directory. Once you've confirmed that mounts have been properly done you can run the command noted here: chroot mnt sysimage. I click OK. I review what's mounted with the mnt command and I can cross check it against my installation by reading my installed fstab configuration file. It's in a mnt sysimage directory, and as you should already know, it's in the etc slash fstab file. And I'll leave the cross checking up to you. But I've confirmed it for myself so I can run chroot mnt sysimage, and now this is mounted as if I've booted normally. But, going into rescue mode bypasses any problems that I may have had with missing kernels, problems with files like etc inittab, or etc fstab. Troubles in bootscripts such as etc slash roc dot sysinit, or even problems with x window configuration files. Now that you know how to do rescue mode you're ready to create your own test problems, or better yet, get the help of a partner. Think of problems you can create in boot files or the other files that I've just mentioned, but before you do that, make sure there is a backup, or at least a VMwear snapshot. If you have problems changing things back, the backup can be a lifesaver. Whatever you do, try rescue mode again and again. You'll be thankful when you finally get to the RHCE exam because knowing rescue mode can help maximize the time you have to solve any problems you encounter.