update-initramfs fails with an error 'Error 24 : Write error : cannot write compressed block'

[Guruprasad]

On a VirtualBox 6.1.14 VM with 2 vCPUs and 8 GB RAM and a 10 GiB hard disk space, I installed Ubuntu 20.10 with ZFS enabled on a full disk installation using the latest installer ISO available on the Ubuntu releases site.

After installation, I booted into the installed OS and tried to install all the package updates. It went mostly fine till when it tried to run the update-initramfs operation and failed. Below are the relevant messages printed to the console.

<snip>
Setting up initramfs-tools (0.137ubuntu12) ...
update-initramfs: deferring update (trigger activated)
Processing triggers for initramfs-tools (0.137ubuntu12) ...
update-initramfs: Generating /boot/initrd.img-5.8.0-25-generic
Error 24 : Write error : cannot write compressed block
E: mkinitramfs failure cpio 141 lz4 -9 -l 24
update-initramfs: failed for /boot/initrd.img-5.8.0-25-generic with 1.
dpkg: error processing package initramfs-tools (--configure):
 installed initramfs-tools package post-installation script subprocess returned error exit status 1
Errors were encountered while processing:
 initramfs-tools
ZSys is adding automatic system snapshot to GRUB menu
</snip>

I checked the free disk space to ensure that there is enough available.

<snip>
guruprasad@groovy:~$ df -h
Filesystem Size Used Avail Use% Mounted on
tmpfs 796M 1.5M 795M 1% /run
/dev/mapper/keystore-rpool 453M 748K 419M 1% /run/keystore/rpool
rpool/ROOT/ubuntu_slz5nq 6.0G 3.9G 2.1G 66% /
tmpfs 3.9G 33M 3.9G 1% /dev/shm
tmpfs 5.0M 4.0K 5.0M 1% /run/lock
tmpfs 4.0M 0 4.0M 0% /sys/fs/cgroup
bpool/BOOT/ubuntu_slz5nq 268M 197M 71M 74% /boot
rpool/USERDATA/guruprasad_bdqa1x 2.1G 32M 2.1G 2% /home/guruprasad
/dev/sda2 512M 19M 494M 4% /boot/efi
rpool/ROOT/ubuntu_slz5nq/var/snap 2.1G 384K 2.1G 1% /var/snap
rpool/ROOT/ubuntu_slz5nq/usr/local 2.1G 512K 2.1G 1% /usr/local
rpool/ROOT/ubuntu_slz5nq/srv 2.1G 256K 2.1G 1% /srv
rpool/ROOT/ubuntu_slz5nq/var/lib 3.0G 933M 2.1G 31% /var/lib
rpool/ROOT/ubuntu_slz5nq/var/www 2.1G 256K 2.1G 1% /var/www
rpool/USERDATA/root_bdqa1x 2.1G 256K 2.1G 1% /root
rpool/ROOT/ubuntu_slz5nq/var/log 2.1G 25M 2.1G 2% /var/log
rpool/ROOT/ubuntu_slz5nq/var/spool 2.1G 384K 2.1G 1% /var/spool
rpool/ROOT/ubuntu_slz5nq/var/games 2.1G 256K 2.1G 1% /var/games
rpool/ROOT/ubuntu_slz5nq/var/mail 2.1G 256K 2.1G 1% /var/mail
rpool/ROOT/ubuntu_slz5nq/var/lib/AccountsService 2.1G 384K 2.1G 1% /var/lib/AccountsService
rpool/ROOT/ubuntu_slz5nq/var/lib/NetworkManager 2.1G 256K 2.1G 1% /var/lib/NetworkManager
rpool/ROOT/ubuntu_slz5nq/var/lib/dpkg 2.2G 59M 2.1G 3% /var/lib/dpkg
rpool/ROOT/ubuntu_slz5nq/var/lib/apt 2.2G 77M 2.1G 4% /var/lib/apt
tmpfs 796M 188K 796M 1% /run/user/1000
</snip>

ProblemType: Bug
DistroRelease: Ubuntu 20.10
Package: initramfs-tools 0.137ubuntu12
ProcVersionSignature: Ubuntu 5.8.0-25.26-generic 5.8.14
Uname: Linux 5.8.0-25-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu50
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
Date: Tue Oct 20 23:05:25 2020
InstallationDate: Installed on 2020-10-20 (0 days ago)
InstallationMedia: Ubuntu 20.10 "Groovy Gorilla" - Beta amd64 (20200930)
PackageArchitecture: all
RebootRequiredPkgs:
 evolution-data-server
 gnome-shell
SourcePackage: initramfs-tools
UpgradeStatus: No upgrade log present (probably fresh install)

[Guruprasad (lgp171188)]

This appears to be because of the limited remaining space in the /boot partition but the partition layout and sizes were automatically configured by the Ubuntu installer, which seems to be the culprit here.

[Guruprasad (lgp171188)]

Uninstalling the older, unused kernel packages doesn't help because zsys takes snapshots of the boot pool before the removal and still eats up a comparable amount of space, thereby not solving the problem at all.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.