Hack and / - Break In Your Boots

New boots, new bootloaders—both take some time to get used to. In this column, find out all the uncomfortable changes in the new GRUB2 bootloader.

A few months ago, I had to replace my favorite pair of shoes: black, suede Converse One Stars (the classic style with no white rubber toe cap, thank you). I had worn the shoes for years, but although most of the shoe held up fine, I had completely worn down the heel. Now, I'm not one to throw away a comfortable pair of shoes. This pair was on its ninth or tenth Shoe-Goo repair, but it finally became hopeless. They had to be replaced. It seemed like a simple task—after all, these shoes had been available all through my adult life, but wouldn't you know, the moment I need another pair, Converse discontinued the model and replaced it with a canvas version with the Chuck Taylor-esque white rubber toe. I had to find a new shoe.

Let me tell you, once you have found the perfect sneaker, it's impossible to find a replacement. Everything I looked at was held up to the standard of the shoe I couldn't have. After a month or two, I finally found shoes that were up to the task, and although I like them, I still miss my old shoes (oh, wouldn't you know it, now that I bought a replacement, Converse has re-released the One Stars how I like them).

I really should be used to this feeling. It seems every few years some open-source project decides to throw away an entire codebase and start from scratch. Although GNOME and KDE have stirred the pot the most with this, I've also lived through the same thing with the Enlightenment Project, the SysV init to Upstart transition, the LILO bootloader being phased out for GRUB, and now GRUB being replaced by GRUB2. For those of you who thought the difference between GRUB2 and GRUB1 was “one”, you are: good at subtraction, a bit of a smart aleck and in for a rude awakening. In this article, I'm going to help you break in your new GRUB2 bootloader, so hopefully some day, it will be as comfortable to you as the original GRUB.


The first question you might ask is why we need a new bootloader at all? What is wrong with GRUB? The answer, according to the GRUB2 developers, is that the original GRUB codebase was rather old and had become unmaintainable. The software continued to get new feature requests (such as supporting new hardware and platforms) that ultimately were beyond the scope of the original code, so the decision was made to scrap it and start from scratch. Because it was a complete rewrite, the developers decided to take the opportunity to make a clean break and redesign the layout and syntax of the configuration files. Along with these changes, GRUB2 has been able to add new features, such as a rescue mode, enhanced graphical menu and splash screen support, full support for UUIDs, and support for non-x86 platforms, such as PowerPC.

Old Boots

Before I go into how GRUB2 has changed things, I'm going to give a quick overview of GRUB1 (or GRUB Legacy, as they are calling it now) to help highlight the changes for those of you who might be unfamiliar with either bootloader. GRUB (and LILO before it) has been the standard bootloader used by the majority of Linux distributions. When you boot your computer and see a menu that lets you choose between different Linux kernels, or between different versions of Linux and Windows in a dual-boot scenario, you probably are using GRUB. GRUB's job is to allow you to choose between one or more operating systems at boot time and then either load the respective kernel and initrd into memory and start the rest of the boot process, or launch the boot code for some other operating system, such as Windows.

GRUB is quite configurable and organizes itself into a few core programs and directories:

  • /boot/grub/menu.lst: this is the default configuration file for GRUB, although on some distributions it is a symlink to /boot/grub/grub.conf. All of GRUB's configuration is in this file, and users edit this file directly to change any GRUB options.

  • /usr/sbin/grub: this is the core GRUB binary that you can use (if you learned all of the syntax) to install GRUB onto your system. The syntax is a bit tricky though, so ultimately, other programs appeared to help automate the process.

  • /usr/sbin/grub-install: this program acts as the front end to /usr/sbin/grub and makes it much simpler to install GRUB to your hard drive.

  • /usr/sbin/update-grub: this script helps automate configuration of the menu.lst file. Instead of having to add new kernels to menu.lst manually, you can run this script, and it will detect kernels available on your system and build the menu.lst for you. In addition, this script can read special configuration options in the comments of menu.lst and further automate the process of providing rescue modes, memtest86+ and other customizations of the file.

Another great feature of GRUB is the fact that even with all of this configuration, if you make a mistake, GRUB allows you to change essentially any configuration option from the boot prompt. At the GRUB menu, you can press the Esc key to change boot options on the fly.


Kyle Rankin is SVP of Security and Infrastructure at Zero, the author of many books including Linux Hardening in Hostile Networks, DevOps Troubleshooting and The Official Ubuntu Server Book, and a columnist for Linux Journal. Follow him @kylerankin