by Roderick W. Smith, rodsmith@rodsbooks.com
-Originally written: 4/19/2012; last Web page update: 4/19/2012, referencing rEFInd 0.2.7
+Originally written: 4/19/2012; last Web page update: +4/24/2016, referencing rEFInd 0.10.3
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Beginning with version 0.2.7, rEFInd has been able to load EFI drivers. Although EFI implementations should be able to do this prior to rEFInd's launch, in my experience, most EFI implementations offer such poor control over EFI driver loading that they can't be counted on to do this. Thus, if you want to use EFI drivers, rEFInd's ability to do so can be useful. This page tells you why you might want to use drivers, where you can go to find them, and provides tips on a few specific drivers.
+Beginning with version 0.2.7, rEFInd has been able to load EFI drivers, and as of version 0.4.0, it has shipped with some EFI filesystem drivers. Although EFI implementations should be able to load drivers prior to rEFInd's launch, in my experience, most EFI implementations offer such poor control over EFI driver loading that they can't be counted on to do this. Thus, if you want to use EFI drivers, rEFInd's ability to do so can be useful. This page tells you why you might want to use drivers, how you can install and use rEFInd's own drivers, where you can go to find other drivers, and provides tips on a few specific drivers.
+ +EFI supports drivers, which can activate hardware or filesystems in the pre-boot environment. At the moment, EFI drivers are few and far between; but you can or might want to use them for various reasons:
Note that most of these uses are theoretical, at least to me; I don't know of any specific examples of EFI drivers (available as separate files) for disk controller hardware, network cards, or video cards. Such drivers are often embedded in the firmware of the devices themselves, and should be loaded automatically by the EFI. Chances are good that a few such drivers are available, unknown to me, and more may become available in the future. If you happen to have a device and need support for it under EFI, searching for drivers is certainly worth doing.
-To the best of my knowledge, the best reason to want EFI driver support in rEFInd is to provide access to filesystems. Although EFI filesystem driver choices are currently limited, those that are available can help to improve your installation and configuration options, particularly if you've found yourself "boxed in" by awkward installation or bugs, such as the dinky ESP that Ubuntu creates by default or the bug that prevents a Linux kernel with EFI stub loader support from booting from the ESP of at least some Macs.
+To the best of my knowledge, the best reason to want EFI driver support in rEFInd is to provide access to filesystems. Although EFI filesystem driver choices are currently somewhat limited, those that are available can help to improve your installation and configuration options, particularly if you've found yourself "boxed in" by awkward installation or bugs, such as the dinky ESP that Ubuntu creates by default or the bug that prevents a Linux kernel with EFI stub loader support from booting from the ESP of at least some Macs.
+ +As a side note, using an ISO-9660 driver can theoretically help you keep the size of a custom Linux boot CD/DVD down to a reasonable value. This is because EFI systems normally boot from optical discs by reading a FAT image file in El Torito format and treating that file as an ESP. If you need to store the kernel both in that file and directly in the ISO-9660 filesystem (to maintain bootability on BIOS systems), that can represent an unwanted extra space requirement. Placing rEFInd and an ISO-9660 driver in the FAT image file should enable you to store the kernel on the disc only once. Unfortunately, this doesn't work in practice. When the ISO-9660 driver is loaded from the El Torito image, the driver discovers that the optical disc is in use and refuses to access it. It's possible to use EFI shell commands to give the ISO-9660 driver access to the shell device, but this causes the El Torito access to go away, which means that anything loaded from the El Torito image (such as rEFInd) is likely to malfunction. Also, some EFI implementations include ISO-9660 drivers, so you might not need a separate ISO-9660 driver if you're building a disc for a particular computer.
+ + +As a side note, using the ISO-9660 driver might help you keep the size of a custom Linux boot CD/DVD down to a reasonable value. This is because EFI systems normally boot from optical discs by reading a FAT image file in El Torito format and treating that file as an ESP. If you need to store the kernel both in that file and directly in the ISO-9660 filesystem (to maintain bootability on BIOS systems), that can represent an unwanted extra space requirement. Placing rEFInd and an ISO-9660 driver in the FAT image file should enable you to store the kernel on the disc only once. Note, however, that this is theoretical; I've not yet tried creating a bootable disc in this way. Also, some EFI implementations include ISO-9660 drivers, so you might not need a separate ISO-9660 driver if you're building a disc for a particular computer.
+ -Since version 0.4.0, rEFInd has shipped with a small collection of read-only EFI filesystem drivers. These are:
-As already noted, I know of no EFI drivers for EFI hardware, aside from those that are built into motherboards' EFI implementations. I do, however, know of a few EFI filesystem drivers:
+All of these drivers rely on filesystem wrapper code written by rEFIt's author, Christoph Phisterer.
+ + + +If you want to use one or more of these drivers, you can install them from the rEFInd binary package from the refind/drivers_arch directory, where arch is a CPU architecture code—x64 or ia32. The files are named after the filesystems they handle, such as ext4_x64.efi for the 64-bit ext4fs driver. You should copy the files for the filesystems you want to use to the drivers or drivers_arch subdirectory of the main rEFInd installation directory. (You may need to create this subdirectory.) Be careful to install drivers only for your own architecture. Attempting to load drivers for the wrong CPU type will cause a small delay at best, or may cause the computer to crash at worst. I've placed rEFInd's drivers in directories that are named to minimize this risk, but you should exercise care when copying driver files.
+ + + +When you reboot after installing drivers, rEFInd should automatically detect and use the drivers you install. There's likely to be an extra delay, typically from one to five seconds, as rEFInd loads the drivers and tells the EFI to detect the filesystems they handle. For this reason, and because of the possibility of drivers harboring bugs, I recommend installing only those drivers that you need. If you like, you can install drivers you don't plan on using to some other directory, such as /drivers on the ESP's root. You can then load these drivers manually with the EFI shell's load command if the need arises in the future. You can then tell the shell to re-assign drive identifiers with map -r:
+ ++fs0: load btrfs_x64.efi +fs0: map -r ++ + +
As already noted, I know of no EFI drivers for EFI hardware, aside from those that are built into motherboards' EFI implementations. I do, however, know of a few EFI filesystem drivers, in addition to those provided with rEFInd:
Most of these cross-project drivers appear to be related. For instance, the ISO-9660 drivers are both based on code written by Christoph Phisterer for rEFIt (although he doesn't seem to have finished and released it in binary form himself).
+The rEFIt, Clover, and VirtualBox drivers are related, and all of them +have fed into rEFInd's drivers. Specific versions can have their own +quirks, though. For instance, the Clover (and I suspect VirtualBox) drivers +don't return volume labels, which causes rEFInd to display loaders on those +volumes as being on a disk called Unknown. (I fixed that bug for +rEFInd's version, and it wasn't present in the original rEFIt drivers.) +Most of these drivers also suffer from speed problems on some computers. +This is worst with the ext2fs drivers under VirtualBox; on my main +computer, that combination takes 3 minutes to load a Linux kernel and +initial RAM disk file! Most real computers don't suffer nearly so badly, +but some can take an extra five seconds or so to boot a kernel. I've fixed +the speed problems in rEFInd's drivers as of version 0.7.0.
+ +Although I know of no readily-available hardware drivers, I do know of a couple of non-hardware non-filesystem drivers:
-As you can see, pickings are rather slim. Nonetheless, they are useful for certain purposes. The options could increase in the future, too. Source code to a wide variety of filesystems is available in GRUB Legacy, GRUB 2, Linux, various BSD kernels, and in other projects. Sooner or later somebody's likely to begin porting those drivers to EFI. If you do so, or if you know of additional EFI drivers, please tell me about it, so I can share the information here. Likewise if you know of a source for other EFI drivers—say, for a video card or disk controller card.
+Once you've obtained an EFI driver or two, you can install it in rEFInd by creating a subdirectory of the rEFInd directory called drivers—for instance, EFI/refind/drivers, if you've installed rEFInd to EFI/refind on the ESP. Alternatively, you can create a directory of any other name and use the scan_driver_dirs option in refind.conf to tell rEFInd where to look for drivers. Either way, rEFInd attempts to load all the EFI drivers from these directories, so placing your files there and rebooting will do the trick.
+rEFInd is likely to take slightly longer to start up when you use drivers, but the effect is likely to be small. On my systems, it's usually just a second or so. This effect could be greater with some drivers or on some systems, though.
+Both of these drivers are useful mainly for developers.
-I've tested the original rEFIt drivers on a handful of systems. First let me re-emphasize one point: To use rEFIt's ext2fs and ReiserFS drivers on a UEFI-based PC, you must separate the x86 and x86-64 binaries from the "fat" binary format that come in the binary package. You can do this with my thin program.
+ -The rEFIt ext2fs driver works on both ext2fs and ext3fs, but not on ext4fs—at least, not in my one test. (There may be options you can use when creating an ext4 filesystem that would enable the rEFIt ext2fs driver to handle it, but if so I don't know what they are.) The ReiserFS driver is obviously useful only on ReiserFS partitions. (Reiser4 is not supported, as far as I know.) Given that these filesystems are getting a bit on in age by Linux standards, you might do well to use them on a separate Linux /boot partition; however, if you're willing to use ext3fs or ReiserFS on your root (/) filesystem, you can use the rEFIt drivers to read your kernel from it. Note that this assumes you use conventional partitions; to the best of my knowledge, there's no EFI driver for Linux's Logical Volume Manager (LVM) or Redundant Array of Independent Disks (RAID) configurations, so the EFI can't access filesystems stored in these ways.
+Driver availability could increase in the future. If you know of +additional EFI drivers, please tell +me about them, so I can share the information here. Likewise if you +know of a source for other EFI drivers—say, for a video card or disk +controller card.
-The ext2fs and ReiserFS drivers work, but they are a bit sluggish—particularly the ext2fs driver. The extent of the problem depends on the computer. In my tests so far, VirtualBox has fared the worse. On it, loading a Linux kernel with EFI stub loader from a FAT partition takes 2 seconds, from the moment of selecting the OS in rEFInd to the moment the kernel messages begin to appear. The equivalent time using ReiserFS is 20 seconds, and with ext2fs it's 200 seconds (that is, 3 minutes and 20 seconds). On a 32-bit Mac Mini, though, the speed problem is much less pronounced—my kernel loads in just 3 seconds from a ReiserFS partition and in 13 seconds from an ext2 filesystem. Times with ext2fs on a UEFI PC with an Intel motherboard were also reasonable, although I didn't record precise values. Nonetheless, if you try the ext2fs driver and it seems to hang, be patient; it may finally boot up. If so, and if the delay is too great for you to accept, you might consider using ReiserFS instead of ext2fs or ext3fs, at least if a change is practical. (For a /boot partition, it almost certainly is practical; you can back it up quite easily, create a fresh filesystem on it, and restore it. You may need to adjust your /etc/fstab entry for a new UUID value, though.)
+Once you've obtained an EFI driver, you can install it in rEFInd just as you would install rEFInd's own drivers, as described earlier.
-Although both ext2fs and ReiserFS are case-sensitive, these drivers treat them in a case-insensitive way. Symbolic links work, which opens up possibilities for configuration, such as using a single kernel binary for multiple Linux distributions, with a link in one subdirectory pointing to a file in another directory. (If you try this, though, be sure to use relative links, as in ../otherdist/bzImage.efi, at least if the partition is not Linux's root filesystem.)
+ +I've tested several of the drivers described on this page on a handful +of systems. The Pfisterer ext2fs driver (from any source) works on both +ext2fs and ext3fs, but not on ext4fs—but Agner's derivative ext4fs +driver handles ext4fs, so that's not a problem. The ReiserFS driver is +obviously useful only on ReiserFS partitions. (Reiser4 is not supported, as +far as I know.) The Btrfs driver is the newest of the Linux filesystem +drivers included with rEFInd, and so I've tested it the least, but it's +worked for me on several test systems. Given that ext2fs, ext3fs, and +ReiserFS are getting a bit on in age by Linux standards, you might do well +to use them on a separate Linux /boot partition; however, if +you're willing to use ext3fs, ext4fs, Btrfs, or ReiserFS on your root +(/) filesystem, you can use the EFI drivers to read your kernel +from it. Note that this assumes you use conventional partitions; to the +best of my knowledge, there's no EFI driver for Linux's Logical Volume +Manager (LVM) or Redundant Array of Independent Disks (RAID) +configurations, so the EFI can't access filesystems stored in these +ways.
+ +As noted earlier, rEFInd's drivers prior to version 0.7.0, as well as related drivers from rEFIt, Clover, and VirtualBox, suffer from speed problems. These problems are mostly minor, adding a second or two to boot times; but on some computers, the speed problems can be dramatic, boosting kernel-load times up to as much as three minutes (under VirtualBox). If you run into excessive boot times with such a driver, try switching to the latest rEFInd driver instead. You might also try Pete Batard's efifs drivers.
+ +Although ext2fs, ext3fs, ext4fs, and ReiserFS are all case-sensitive, these drivers treat them in a case-insensitive way. Symbolic links work; however, rEFInd 0.6.11 and later ignore symbolic links, since many distributions use them in a way that creates redundant or non-functional entries in the rEFInd menu. You should be able to use hard links if you want to use a single kernel file in multiple ways (say for two distributions).
copyright © 2012 by Roderick W. Smith
+copyright © 2012–2016 by Roderick W. Smith
This document is licensed under the terms of the GNU Free Documentation License (FDL), version 1.3.