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Instead of parsing the output of mount, use mountpoint to check if the ESP is mounted. This should be slightly less fragile than parsing text formatted for human consumption. |
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etc/zfsbootmenu | ||
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README.md | ||
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void-install.md |
README.md
Introduction
zfsbootmenu is implemented as a Dracut module to provide an experience similar to FreeBSD's bootloader, for Linux distributions. In broad strokes, it works as follows:
- Via GRUB, direct EFI booting, etc, boot a Linux kernel along with an initramfs containing ZFS Boot Menu
- Look for
zfsbootmenu
on the kernel command line- Optionally specify a default pool (if multiple are present)
- Find all healthy pools and then import them
- If a specific pool was set, look for the bootfs pool value. Prefer this boot environment.
- If no pool was defined on the command line, use the bootfs value on the first-found pool
- If a bootfs value is defined, start a 10 second countdown to boot that environment with the highest kernel found in /boot
- If no bootfs value is defined, find every filesystem that mounts to / with a /boot directory, and find every kernel. Prompt via fzf.
- If needed, prompt for encryption passphrases
- Once the count down has been reached for the bootfs-selected environment, prompt for the encryption passphrase if needed
- Mount the filesystem and find the highest-numbered kernel in /boot in the boot environment.
- Load the kernel, initramfs and the kernel command line defined in the
org.zfsbootmenu:commandline
property (or, as a fallback,/etc/default/grub
) into memory via kexec - Unmount all ZFS filesystems
- Boot the final kernel and initramfs
At this point, you'll be booting into your OS-managed kernel and initramfs, along with any arguments needed to correctly boot your system.
This tool makes uses of the following additional software:
- fzf
- kexec-tools
- mbuffer
- Linux Kernel
- ZFS on Linux (currently 0.8.3 built on Void Linux).
Binary releases for x86_64 and ppc64le are built on Void Linux hosts. ZFSBootMenu has been successfully tested up to ZFS on Linux 0.8.3 and Dracut 49.
System prereqs
To ensure the boot menu can find your kernels, you'll need to ensure /boot
resides on your ZFS file system. An example filesystem layout is as follows:
NAME USED AVAIL REFER MOUNTPOINT
zroot 278G 582G 96K none
zroot/ROOT 10.9G 582G 96K none
zroot/ROOT/void.2019.10.04 1.20M 582G 7.17G /
zroot/ROOT/void.2019.11.01 10.9G 582G 7.17G /
zroot/home 120G 582G 11.8G /home
There are two boot environments created, identified by mounting to /. The environment that this system will boot into is defined by the bootfs
value set on the zroot
zpool.
NAME PROPERTY VALUE SOURCE
zroot bootfs zroot/ROOT/void.2019.11.01 local
On start, ZFS Boot Menu will find the highest versioned kernel in zroot/ROOT/void.2019.11.01/boot
, confirm that a matching initramfs is present, and default to booting the OS with that.
Installation
Kernel command-line arguments should be set by setting the ZFS property org.zfsbootmenu:commandline
on each boot environment. If the property is not defined for a boot environment or its parents, command-line arguments will be taken from the GRUB_CMDLINE_LINUX_DEFAULT
variable in the file /etc/default/grub
of the boot environment if the file exist and the variable is defined. Do not set any root=
or any other pool-related options in the kernel command line; these will be filled in automatically when a boot environment is selected.
For example, I have the following command-line arguments set on my boot environment:
zfs.zfs_arc_max=8589934592 elevator=noop
Because ZFS properties are inherited by default, it is possible to set the org.zfsbootmenu:commandline
property on a common parent to apply the same arguments to multiple environments. Setting the property locally on individual boot environments will override the common defaults.
EFI
ZFS Boot Menu integrates nicely with an EFI system. There will be two key things to configure here.
- The mountpoint of the EFI partition and it's contents
- The mountpoint of the boot environment
/boot
and it's contents
Each boot environment should have /boot
live on the ZFS filesystem. Using the above example, zroot/ROOT/void.2019.11.01
would contain /boot
with any kernel/initramfs pairs.
# ls /boot
config-5.3.18_1
config-5.4.6_1
efi
initramfs-5.3.18_1.img
initramfs-5.4.6_1.img
System.map-5.3.18_1
System.map-5.4.6_1
vmlinuz-5.3.18_1
vmlinuz-5.4.6_1
Once /boot
is backed by ZFS in a boot environment, you'll need to install the boot menu files. Typically, EFI partitions are mounted to /boot/efi
, and contain a number of sub-directories. In this example, /boot/efi/EFI/void
holds the ZFS Boot Menu kernel and initramfs.
# lsblk -f /dev/sda
NAME FSTYPE LABEL UUID FSAVAIL FSUSE% MOUNTPOINT
sdg
├─sda1 vfat AFC2-35EE 7.9G 1% /boot/efi
└─sda2 swap 412401b6-4aec-4452-a6bd-6fc20fbdc2a5 [SWAP]
# ls /boot/efi/EFI/void/
initramfs-0.7.4.img
initramfs-0.7.5.img
vmlinuz-0.7.4
vmlinuz-0.7.5
With this layout, you'll now need a way to boot the kernel and initramfs via EFI. This can be done via a manual entry set via efibootmgr, or it can be done with rEFInd.
If you are using a pre-built kernel and initramfs downloaded from the releases page, you'll need to identify the following additional details:
- Your system's hostid (
hostid
). It's important that this command is executed as root, to ensure that it returns the correct value. - Your boot pool name, if you have multiple.
- The disk path and partition index of your EFI partition. (/dev/sda, part 1)
efibootmgr
efibootmgr --disk /dev/sda \
--part 1 \
--create \
--label "ZFS Boot Menu" \
--loader /vmlinuz-0.7.5 \
--unicode 'root=zfsbootmenu:POOL=zroot ro initrd=\EFI\void\initramfs-0.7.5.img quiet spl_hostid=a8c0a2a8' \
--verbose
Take note to adjust zfsbootmenu:POOL=
, spl_hostid=
, --disk
and --part
to match your system configuration.
Each time the bootmenu is updated, a new EFI entry will need to be manually added.
rEFInd
rEFInd
is considerably easier to install and manage. Refer to your distributions packages for installation. Once rEFInd has been installed, you can create refind_linux.conf
in the directory holding the ZFS Boot Menu files (/boot/efi/EFI/void
in our example):
"Boot Default BE" "ro quiet loglevel=0 timeout=0 zfsbootmenu:POOL= spl_hostid="
"Select BE" "ro quiet loglevel=0 timeout=-1 zfsbootmenu:POOL= spl_hostid="
As with the efibootmgr section, the zfsbootmenu:POOL=
and spl_hostid=
options need to be configured to match your environment.
This file will configure rEFInd
to create two entries for each kernel and initrams pair it finds. The first will directly boot into the environment set via the bootfs
pool property. The second will force ZFS Boot Menu to display an environment / kernel / snapshot selection menu, allowing you to boot alternate environments, kernels and snapshots.
Command line options
ZFS Boot Menu currently understands the following options:
spl_hostid=
used to set the system hostid if you are using a pre-built initramfs from the release page.force_import=0|1
set to1
to attempt to force import all pools on the system. Use with caution!read_write=0|1
set to1
to enable writes to pools when importing. Pools are imported read-only by default as a safety precaution.timeout=
- A value of
0
will result in the system immediately booting from the pool configured in thebootfs
pool property - A value of
-1
will result in the system displaying a boot menu. - Any other positive value will show a countdown timer to boot the environment configured under
bootfs
, otherwise it will default to a boot menu. ""|zfsbootmenu|zfsbootmenu:|zfsbootmenu:POOL=zroot
The first three values are functionally identical. The fourth can be used to prefer a pool if multiple are present in the system.
ZFS properties
The following properties can be set at whatever level of the pool you'd prefer to control the boot behavior.
org.zfsbootmenu:kernel
this can be a partial kernel name(5.4)
or an explicit name(vmlinuz-5.6.11_1)
.org.zfsbootmenu:commandline
set the list of kernel commandline options to be passed to the final OS. Do not setroot=
, this is set for you.org.zfsbootmenu:active
controls whether boot environments appear in or are hidden from ZFS Boot Menu:- If a boot environment has the property
mountpoint=/
, setorg.zfsbootmenu:active=off
to hide the environment. For any other value, including not set, the boot environment will be shown. - If a boot environment has the property
mountpoint=legacy
, setorg.zfsbootmenu:active=on
to show the environment. For any other value, including not set, the boot environment will be hidden.
- If a boot environment has the property
initramfs creation
bin/generate-zbm
can be used to create an initramfs on your system. It ships with void-specific defaults in etc/config.ini
. To create an initramfs, the following additional tools/libraries will need to be available on your system:
If you want to create an unified EFI file (kernel, initramfs, command line), you will also need:
- linuxx64.efi.stub (typically packaged with gummiboot)
Your distribution should have packages for these already.
config.ini
/etc/zfsbootmenu/config.ini
is used to control the behavior of generate-zbm. An example is documented below.
[Global]
ManageImages=0
DracutConfDir=/etc/zfsbootmenu/dracut.conf.d
[Kernel]
CommandLine="ro quiet loglevel=0"
[Components]
ImageDir=/boot/efi/EFI/void
Versioned=1
Copies=3
[EFI]
ImageDir=/boot/efi/EFI/void
Versioned=1
Copies=0
Global
ManageImages
Set this to 1 to allow generate-zbm to perform any actions (creation, removal of old files, etc)DracutConfDir
Set this to the location of the dracut configuration director for ZFS Boot Menu. This CAN NOT be the same location as the systemdracut.conf.d
, as the configuration files there directly conflict with the creation of the bootmenu initramfs.
Kernel
CommandLine
If you're making a unified EFI file, this is the command line passed to the module. Refer to Command line options.
Components
ImageDir
This is the destination directory for the initramfs and kernel.Versioned
Set to 1 to create versioned files. Set to 0 to disable a version suffix, which is useful if you have static bootloader entries pointing to ZFS Boot Menu.Copies
This controls the number of copies to keep, in addition to the file that is currently being created.
EFI
ImageDir
This is the destination directory for the unified EFI file.Versioned
Set to 1 to create versioned files. Set to 0 to disable a version suffix, which is useful if you have static bootloader entries pointing to ZFS Boot Menu.Copies
This controls the number of copies to keep, in addition to the file that is currently being created.Stub
This is the path to the stub loader used to boot the unified EFI image. If not set, a default of/usr/lib/gummiboot/linuxx64.efi.stub
is assumed.
Native encryption
ZFS Boot Menu can import pools or filesystems with native encryption enabled. If your boot environments are not encrypted but say /home is, you will not receive a decryption prompt. To ensure that you can decrypt your pool to load the kernel and initramfs, you'll need to you have the filesystem parameters configured correctly.
zfs get all zroot | egrep '(encryption|keylocation|keyformat)'
zroot encryption aes-256-gcm -
zroot keylocation file:///etc/zfs/zroot.key local
zroot keyformat passphrase -
zroot encryptionroot zroot -
It's critical that keyformat
is set to passphrase
, otherwise you'll be unable to enter the correct value in the boot loader. ZoL currently only supports one key, but it does have a behavior that we can exploit. If you configure the keylocation
value to a file on disk, put your passphrase in that, and then put that file into the FINAL initramfs, you won't receive a second password prompt on boot. You'll then still receive a password prompt in the boot loader, since we can force a prompt for passphrase input.
For Dracut-based systems, this can be done by creating /etc/dracut.conf.d/zol.conf
with the following contents:
install_items+=" /etc/zfs/zroot.key "
It's critical that you do not put this key file into the ZFS Boot Menu initramfs, since that file exists on an unencrypted volume - leaving your pool essentially wide-open.
Limitations
When building a kernel command line to pass to the kexec'd kernel, the command line generated is always created for Dracut's ZFS module. Again, this will need to be modified based on the detected OS in the boot environment.
Both of the above issues are readily resolved by hopefully reading /etc/os-release from the boot environment and acting based on that.