Linux on UEFI:
A Quick Installation Guide

by Roderick W. Smith,

Originally written: 10/19/2013; last modified: 3/16/2015

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For several years, a new firmware technology has been lurking in the wings, unknown to most ordinary users. Known as the Extensible Firmware Interface (EFI), or more recently as the Unified EFI (UEFI, which is essentially EFI 2.x), this technology has begun replacing the older Basic Input/Output System (BIOS) firmware with which most experienced computer users are at least somewhat familiar.

This page is a quick introduction to EFI for Linux users, including advice on getting started installing Linux to such a computer. Unfortunately, EFI is a dense topic; the EFI software itself is complex, and many implementations have system-specific quirks and even bugs. Thus, I cannot describe everything you'll need to know to install and use Linux on an EFI computer on this one page. It's my hope that you'll find this page a useful starting point, though, and links within each section and in the References section at the end will point you toward additional documentation.

Does Your Computer Use EFI?

EFI is a type of firmware, meaning that it's software built into the computer to handle low-level tasks. Most importantly, the firmware controls the computer's boot process, which in turn means that EFI-based computers boot differently than do BIOS-based computers. (A partial exception to this rule is described shortly.) This difference can greatly complicate the design of OS installation media, but it has little effect on the day-to-day operation of the computer, once everything is set up and running. Note that most manufacturers use the term "BIOS" to refer to their EFIs. I consider this usage confusing, so I avoid it; in my view, EFIs and BIOSes are two different types of firmware.

EFI has been used on Intel-based Macs since they were first introduced in 2006. Beginning in late 2012, most computers that ship with Windows 8 or later boot using UEFI by default, and in fact most PCs released since mid-2011 use UEFI, although they may not boot in EFI mode by default. A few PCs sold prior to 2011 also support EFI, although most such computers boot in BIOS mode by default.

If you're uncertain about your computer's EFI support status, you should check your firmware setup utility and your user manual for references to EFI, UEFI, or legacy booting. (Searching a PDF of your user manual can be a quick way to do this.) If you find no such references, your computer probably uses an old-style ("legacy") BIOS; but if you find references to these terms, it almost certainly uses EFI. You can also try booting a medium that contains only an EFI-mode boot loader. The USB flash drive or CD-R image of rEFInd is a good choice for this test.

Before proceeding further, you should understand that most EFIs on x86 and x86-64 computers include a component known as the Compatibility Support Module (CSM), which enables the EFI to boot OSes using the older BIOS-style boot mechanisms. This can be a great convenience because it provides backwards compatibility; but it also creates complications because there's no standardization in the rules and user interfaces for controlling when a computer boots in EFI mode vs. when it boots in BIOS (aka CSM or legacy) mode. In particular, it's far too easy to accidentally boot your Linux installation medium in BIOS/CSM/legacy mode, which will result in a BIOS/CSM/legacy-mode installation of Linux. This can work fine if Linux is your only OS, but it complicates the boot process if you're dual-booting with Windows in EFI mode. (The opposite problem can also occur.) The following sections should help you boot your installer in the right mode. If you're reading this page after you've installed Linux in BIOS mode and want to switch boot modes, read the upcoming section, Oops: Converting a Legacy-Mode Install to Boot in EFI Mode.

One optional feature of UEFI deserves mention: Secure Boot. This feature is designed to minimize the risk of a computer becoming infected with a boot kit, which is a type of malware that infects the computer's boot loader. Boot kits can be particularly difficult to detect and remove, which makes blocking them a priority. Microsoft requires that all desktop and laptop computers that bear a Windows 8 logo ship with Secure Boot enabled. This type of configuration complicates Linux installation, although some distributions handle this problem better than do others. Do not confuse Secure Boot with EFI or UEFI, though; it's possible for an EFI computer to not support Secure Boot, and it's possible to disable Secure Boot even on x86-64 EFI computers that support it. Microsoft requires that users can disable Secure Boot for Windows 8 certification on x86 and x86-64 computers; however, this requirement is reversed for ARM computers—such computers that ship with Windows 8 must not permit the user to disable Secure Boot. Fortunately, ARM-based Windows 8 computers are currently rare. I recommend avoiding them.

Does Your Distribution Support EFI?

Most Linux distributions have supported EFI for years. The quality of that support varies from one distribution to another, though. Most of the major distributions (Fedora, OpenSUSE, Ubuntu, and so on) provide good EFI support, including support for Secure Boot. Some more "do-it-yourself" distributions, such as Gentoo, have weaker EFI support, but their nature makes it easy to add EFI support to them. In fact, it's possible to add EFI support to any Linux distribution: You need to install it (even in BIOS mode) and then install an EFI boot loader on the computer. See the Oops: Converting a Legacy-Mode Install to Boot in EFI Mode section for information on how to do this.

You should check your distribution's feature list to determine if it supports EFI. You should also pay attention to your distribution's support for Secure Boot, particularly if you intend to dual-boot with Windows 8. Note that even distributions that officially support Secure Boot may require that this feature be disabled, since Linux Secure Boot support is often poor or creates complications.

Preparing to Install Linux

A few preparatory steps will help make your Linux installation on an EFI-based computer go more smoothly:

  1. Upgrade your firmware—Some EFIs are badly broken, but hardware manufacturers occasionally release updates to their firmware. Thus, I recommend upgrading your firmware to the latest version available. If you know from forum posts or the like that your EFI is problematic, you should do this before installing Linux, because some problems will require extra steps to correct if the firmware is upgraded after the installation. On the other hand, upgrading firmware is always a bit risky, so holding off on such an upgrade may be best if you've heard good things about your manufacturer's EFI support.
  2. Learn how to use your firmware—You can usually enter a firmware setup utility by hitting the Del key or a function key early in the boot process. Check for prompts soon after you power on the computer or just try each function key. Similarly, the Esc key or a function key usually enters the firmware's built-in boot manager, which enables you to select which OS or external device to boot. Some manufacturers are making it hard to reach such settings. In some cases, you can do so from inside Windows 8, as described on this page.
  3. Adjust the following firmware settings:
  4. Disable the Windows Fast Startup featureThis page describes how to disable this feature, which is almost certain to cause filesystem corruption if left enabled. Note that this feature is distinct from the firmware's fast boot feature.
  5. Check your partition table—Using GPT fdisk, parted, or any other partitioning tool, check your disk's partitions. Ideally, you should create a hardcopy that includes the exact start and end points (in sectors) of each partition. This will be a useful reference, particularly if you use a manual partitioning option in the installer. If Windows is already installed, be sure to identify your EFI System Partition (ESP), which is a FAT partition with its "boot flag" set (in parted or GParted) or that has a type code of EF00 in gdisk.

Installing Linux

Most Linux distributions provide adequate installation instructions; however, I've observed a few common stumbling blocks on EFI-mode installations:

In some cases, you may be forced to install Linux in BIOS mode. You can sometimes then manually install an EFI-mode boot loader for Linux to begin booting in EFI mode. See my Managing EFI Boot Loaders for Linux page for information on available boot loaders and how to install them.

Fixing Post-Installation Problems

If you can't seem to get an EFI-mode boot of Linux working but a BIOS-mode boot works, you can abandon EFI mode entirely. This is easiest on a Linux-only computer; just install a BIOS-mode boot loader (which the installer should have done if you installed in BIOS mode). If you're dual-booting with an EFI-mode Windows, though, the easiest solution is to install my rEFInd boot manager. Install it from Windows and edit the refind.conf file: Uncomment the scanfor line and ensure that hdbios is among the options. This will enable rEFInd to redirect the boot process to a BIOS-mode boot loader. This solution works for many systems, but sometimes it fails for one reason or another.

If you reboot the computer and it boots straight into Windows, it's likely that your Linux boot loader or boot manager was not properly installed. (You should try disabling Secure Boot first, though; as I've said, it often causes problems.) There are several possible solutions to this problem:

Another class of problems relates to boot loader troubles—If you see GRUB (or whatever boot loader or boot manager your distribution uses by default) but it doesn't boot an OS, you must fix that problem. Windows often fails to boot because GRUB 2 is very finicky about booting Windows. This problem can be exacerbated by Secure Boot in some cases. See my page on GRUB 2 for a sample GRUB 2 entry for booting Windows. Linux boot problems, once GRUB appears, can have a number of causes, and are likely to be similar to BIOS-mode Linux boot problems, so I don't cover them here.

Despite the fact that it's very common, my opinion of GRUB 2 is rather low—it's an immensely complex program that's difficult to configure and use. Thus, if you run into problems with GRUB, my initial response is to replace it with something else. My Web page on EFI boot loaders for Linux describes the options that are available. These include my own rEFInd boot manager, which is much easier to install and maintain, aside from the fact that many distributions do manage to get GRUB 2 working—but if you're considering replacing GRUB 2 because of its problems, that's obviously not worked out for you!

Beyond these issues, EFI booting problems can be quite idiosyncratic, so you may need to post to a Web forum for help. Be sure to describe the problem as thoroughly as you can. The Boot Info Script can provide useful information—run it and it should produce a file called RESULTS.txt that you can paste into your forum post. Be sure to precede this pasted text with the string [code] and follow it with [/code], though; otherwise people will complain. Alternatively, upload RESULTS.txt to a pastebin site, such as, and post the URL that the site gives you.

Oops: Converting a Legacy-Mode Install to Boot in EFI Mode

As of early 2015, one very common problem I see in online forums is that people follow bad instructions and install Linux in BIOS mode to dual-boot with an existing EFI-mode Windows installation. This configuration works poorly because most EFIs make it difficult to switch between boot modes, and GRUB can't handle the task, either. You might also find yourself in this situation if you've got a very flaky EFI that simply won't boot an external medium in EFI mode, or if you have video or other problems with Linux when it's booted in EFI mode.

As noted earlier, in Fixing Post-Installation Problems, one possible solution to such problems is to install rEFInd in Windows and configure it to support BIOS-mode boots. You can then boot rEFInd and chainload to your BIOS-mode GRUB. I recommend this fix mainly when you have EFI-specific problems in Linux, such as a failure to use your video card. If you don't have such EFI-specific problems, installing rEFInd and a suitable EFI filesystem driver in Windows will enable you to boot Linux directly in EFI mode. This can be a perfectly good solution, and it will be equivalent to what I describe next.

In most cases, it's best to configure Linux to boot in EFI mode. There are many ways to do this, but the best way requires using an EFI-mode boot of Linux (or conceivably Windows or an EFI shell) to register an EFI-mode version of your preferred boot manager. One way to accomplish this goal is as follows:

  1. Download a USB flash drive or CD-R version of my rEFInd boot manager.
  2. Prepare a medium from the image file you've downloaded. You can do this from any computer, booted in either EFI or BIOS mode (or in other ways on other platforms).
  3. If you've not already done so, disable Secure Boot. This is necessary because the rEFInd CD-R and USB images don't support Secure Boot. If you want to keep Secure Boot, you can re-enable it later.
  4. Boot rEFInd on your target computer. As described earlier, you may need to adjust your firmware settings and use the built-in boot manager to select your boot medium. The option you select may need to include the string UEFI in its description.
  5. In rEFInd, examine the boot options. You should see at least one option for booting a Linux kernel (with a name that includes the string vmlinuz). Boot it in one of two ways: In some rare cases, you may need to add other kernel options instead of or in addition to a root= option. Gentoo with an LVM configuration requires dolvm, for example.
  6. Once Linux is booted, install your desired boot program. rEFInd is usually pretty easy to install via the RPM, Debian package, PPA, or binary .zip file referenced on the rEFInd downloads page. On Ubuntu and similar distributions, Boot Repair can fix your GRUB setup relatively simply, but it will be a bit of a leap of faith that it will work correctly. (It usually works fine, but in some cases it will make a hash of things.) Other options are described on my Managing EFI Boot Loaders for Linux page.
  7. If you want to boot with Secure Boot active, reboot and enable it. Note, however, that you may need to take extra installation steps to set up your boot program to use Secure Boot. Consult my page on the topic or your boot program's Secure Boot documentation for details.
When you reboot, you should see the boot program you just installed. If the computer instead boots into a BIOS-mode version of GRUB, you should enter your firmware and disable the BIOS/CSM/legacy support, or perhaps adjust your boot order options. If the computer boots straight to Windows, then you should read the preceding section, Fixing Post-Installation Problems.

You may want or need to tweak your configuration at this point. It's common to see extra boot options, or for an option you want to not be visible. Consult your boot program's documentation to learn how to make such changes.

References and Additional Information

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