XBOOTLDR Configuration

I am a PopOS user, and recently I want to test kernels modified and compiled by myself. When installing the kernels, I have errors complaining about /boot/efi is full. I decide to go for the XBOOTLDR option which should allow me to extend the EFI partition, and it can be upto 32GB (max size of FAT32).

Here’s the documentation I used: https://wiki.archlinux.org/title/Systemd-boot

XBOOTLDR is an optional ‘extended boot loader partition’ that systemd-boot can read from the same physical disk as the ESP. It allows storing additional kernels and initrds safely without touching the main EFI partition.

Step 1 : Prepare the partition

Because I need to shrink my root partition, I booted into PopOS recovery. Then I used gparted. After getting some empty space, I created an 8GB primary partition in FAT32, then I also toggle its esp flag on.

Step 2 : Mount the partition

Went back to my regular PopOS, I added this line to /etc/fstab

UUID=4282-6209 /boot/xbootldr  vfat  defaults,umask=0077  0  2

Here, the UUID is derived from (nvme0n1p5 is the created partition)

> blkid /dev/nvme0n1p5
/dev/nvme0n1p5: LABEL_FATBOOT="XBOOTLDR" LABEL="XBOOTLDR" UUID="4282-6209" BLOCK_SIZE="512" TYPE="vfat" PARTLABEL="5"

Now, umount -a will mount this XBOOTLDR partition at boot/xbootldr.

Step 3 : Set the parition type

In that ArchWiki page, it says: The XBOOTLDR partition must have a partition type GUID of bc13c2ff-59e6-4262-a352-b275fd6f7172 [1] (ea00 type for gdisk, xbootldr type for fdisk).

So I changed the partition type via gdisk

# sudo gdisk /dev/nvme0n1

Command (? for help): t
Partition number (1-5): 5
Current type is EA00 (XBOOTLDR partition)
Hex code or GUID (L to show codes, Enter = EA00): ea00
Changed type of partition to 'XBOOTLDR partition'

Command (? for help): w
Do you want to proceed? (Y/N): Y

Without setting the partition type, next command will fail.

Step 4 : Tell bootctl about this partition (might not need)

Then, run this command

sudo bootctl --esp-path=/boot/efi --boot-path=/boot/xbootldr/ install

Since bootctl list output didn’t change after this command (reboot needed), I am not sure if this command is really needed.

Step 5 : Adding image and config in XBOOTLDR

Here’s my original efi folder

/b/efi# ls loader/entries/
# Pop_OS-current.conf  Recovery-CDAE-FADF.conf

/b/efi# cat loader/entries/Pop_OS-current.conf 
# title Pop!_OS
# linux /EFI/Pop_OS-e1db91ab-9998-4921-ac70-317989e51806/vmlinuz.efi
# initrd /EFI/Pop_OS-e1db91ab-9998-4921-ac70-317989e51806/initrd.img
# options root=UUID=e1db91ab-9998-4921-ac70-317989e51806 ro quiet loglevel=0 systemd.show_status=false splash

/b/efi# ls EFI/Pop_OS-e1db91ab-9998-4921-ac70-317989e51806/
# cmdline  initrd.img  vmlinuz.efi

I followed the same pattern to add kernel images in the xbootldr folder

/b/xbootldr# ls loader/entries/
# linux-6.19-rc7-chezhaocheng-lfx-0.conf  linux-current.conf

/b/xbootldr# cat loader/entries/linux-current.conf
# title   Pop!_OS Current [xbootldr]
# linux   /EFI/Linux/vmlinuz-current
# initrd  /EFI/Linux/initrd-current.img
# options root=UUID=e1db91ab-9998-4921-ac70-317989e51806 ro quiet

/b/xbootldr# cat loader/entries/linux-6.19-rc7-chezhaocheng-lfx-0.conf 
# title   Linux 6.19.0-rc7-chezhaocheng-lfx-0+
# linux   /EFI/Linux/vmlinuz-6.19.0-rc7-chezhaocheng-lfx-0+
# initrd  /EFI/Linux/initrd.img-6.19.0-rc7-chezhaocheng-lfx-0+
# options root=UUID=e1db91ab-9998-4921-ac70-317989e51806 ro quiet splash

/b/xbootldr# ls EFI/Linux/
# initrd-current.img
# initrd.img-6.19.0-rc7-chezhaocheng-lfx-0+
# vmlinuz-6.19.0-rc7-chezhaocheng-lfx-0+
# vmlinuz-current

Updates to the xbootldr/loader or xbootldr/EFI won’t reflect in bootctl list output in real time. So debug is a bit difficult, but a reboot will show you if those works.

Result

Boot Image

So now I have the original EFI entries, AND my custom built linux kernels.