Ubuntu 22.04 with multiple disks and (U)EFI booting
One of the traditional and old problems with UEFI booting on servers is that it
had a bad story if you wanted to be able to boot off multiple disks.
Each disk needed its own EFI System Partition (ESP) and you either
manually kept them in synchronization (perhaps via
rsync in a
cron job) or put them in a Linux software RAID mirror with the RAID
superblock at the end and hope hard that nothing ever went wrong.
To my surprise, the state of things seems to be rather better in
Ubuntu 22.04, although there are still traps.
Modern Linuxes don't put much in the ESP, and in particular even
Fedora no longer puts frequently changing things there. In Ubuntu 22.04, what's there in the
EFI/ubuntu subdirectory is a few GRUB binaries and a stub
that tells GRUB where to find your real /boot/grub/grub.cfg, which
normally lives in your root filesystem. All of these are installed
into /boot/efi by running '
or into some other location by running '
(On a 64-bit Ubuntu 22.04 EFI booted system, '
will usefully tell you that the default target type is '
although the manual page will claim otherwise.)
This lets you manually maintain two or more ESPs; just mount the
second one somewhere (perhaps temporarily) and run grub-install
against it. Ubuntu has added a script to do more or less this (cf),
/usr/lib/grub/grub-multi-install, which is normally run by EFI grub
package postinstalls as '
This script will run through a list of configured ESPs, mount them
temporarily (if they're not already mounted), and update them with
grub-install. In the 22.04 server installer, if you mark additional
disks as extra boot drives, it will create an ESP partition on them
and add them to this list of configured ESPs.
(I believe that you can run this script by hand if you want to.)
The list of configured ESPs is stored in a debconf selection,
grub-efi/install_devices'; there are also a number of other
related grub-efi/ debconf selections. An important thing to know
is that configured ESPs are listed using their disk's ID, as
/dev/disk/by-id/<something> (which is perfectly sensible and
perhaps the only sane way to do it). This means that if one of your
boot disks fails and is replaced, the list of configured ESPs won't
include the new disk (even if you made an ESP on it) and will (still)
include the old one. Apparently one fix is to reconfigure a relevant
GRUB package, such as (I think) '
from this AskUbuntu answer.
(In the usual Debian and Ubuntu way, one part of this setup is that
a package upgrade of GRUB may someday abruptly stop to quiz you
about this situation, if you've replaced a disk but not reconfigured
things since. Also, I don't know if there's a better way to see
this list of configured ESPs other than '
grep ...' or maybe '
Life would be nicer if you could set Ubuntu 22.04 to just install
or update GRUB on all valid ESPs that it found, but the current
situation isn't bad (assuming that the reconfigure works; I haven't
tested it, since we just started looking into this today). The
reconfiguration trick is an extra thing to remember, but at least
we're already used to running grub-install on BIOS boot systems.
I'm also not sure I like having
/boot/efi listed in /etc/fstab
and mounted, since it's non-mirrored; if that particular disk fails,
you could have various issues.
(In looking at this I discovered that some of our systems were mounting /boot/efi from their second disk instead of their first one. I blame the Ubuntu 22.04 server installer for reasons beyond the scope of this aside.)
PS: On a BIOS boot system, the '
can be a software RAID array name, which presumably means 'install
boot blocks on whatever devices are currently part of this RAID
array'. I assume that UEFI boot can't be supported this way because
there would be more magic in going from a software RAID array to the
ESP partitions (if any) on the same devices.
PPS: Someday Ubuntu may let you configure both BIOS and UEFI boot on the same system, which would have uses if you want to start off with one but preserve your options to switch to the other for various reasons. We'd probably use it on our servers.
Comments on this page:Written on 09 August 2022.