package usrmerge 25ubuntu2 failed to install/upgrade: installed usrmerge package post-installation script subprocess returned error exit status 255

Trying to upgrade from 20.04 to 22.04

usrmerge doesn't have enough space in /usr and/or /var - the pre-upgrade checks should anticipate this.

=====
Could not install the upgrades

The upgrade has aborted. Your system could be in an unusable state. A
recovery will run now (dpkg --configure -a).

Setting up usrmerge (25ubuntu2) ...
Smartmatch is experimental at /usr/lib/usrmerge/convert-usrmerge line 172.
1766740 KB in /usr but 2116336 KB are required!
dpkg: error processing package usrmerge (--configure):
 installed usrmerge package post-installation script subprocess returned error exit status 255
Errors were encountered while processing:
 usrmerge

Upgrade complete

The upgrade has completed but there were errors during the upgrade
process.
=====

=====
# dpkg --configure -a
Setting up usrmerge (25ubuntu2) ...
Smartmatch is experimental at /usr/lib/usrmerge/convert-usrmerge line 172.
1767220 KB in /usr but 2116336 KB are required!
dpkg: error processing package usrmerge (--configure):
 installed usrmerge package post-installation script subprocess returned error exit status 255
Errors were encountered while processing:
 usrmerge
=====

This requires non-trivial file system resizing that ordinary users won't be able to manage without help.

This shouldn't happen.

Fortunately, I have enough space in my LVM system. I can shrink /home to free up space for increasing the size of /usr - but other might not have that luxury:

root@christina:~# df -h
Filesystem Size Used Avail Use% Mounted on
tmpfs 796M 1.4M 795M 1% /run
/dev/mapper/vg00-rootlv 3.8G 2.2G 1.5G 60% /
/dev/mapper/vg00-usrlv 6.6G 4.9G 1.4G 79% /usr
tmpfs 3.9G 0 3.9G 0% /dev/shm
tmpfs 5.0M 0 5.0M 0% /run/lock
tmpfs 3.9G 0 3.9G 0% /sys/fs/cgroup
/dev/mapper/vg00-varlv 9.5G 7.1G 2.1G 78% /var
/dev/vda1 921M 244M 614M 29% /boot
tmpfs 796M 36K 796M 1% /run/user/131
tmpfs 796M 0 796M 0% /run/user/1000
/dev/mapper/vg00-homelv 75G 48G 24G 68% /home

ProblemType: Package
DistroRelease: Ubuntu 22.04
Package: usrmerge 25ubuntu2
ProcVersionSignature: Ubuntu 5.4.0-135.152-generic 5.4.212
Uname: Linux 5.4.0-135-generic x86_64
ApportVersion: 2.20.11-0ubuntu82.3
Architecture: amd64
CasperMD5CheckResult: unknown
Date: Mon Dec 26 14:41:48 2022
ErrorMessage: installed usrmerge package post-installation script subprocess returned error exit status 255
InstallationDate: Installed on 2013-04-18 (3539 days ago)
InstallationMedia: Ubuntu-Server 12.04 LTS "Precise Pangolin" - Release amd64 (20120424.1)
PackageArchitecture: all
Python3Details: /usr/bin/python3.10, Python 3.10.6, python3-minimal, 3.10.6-1~22.04
PythonDetails: N/A
RebootRequiredPkgs: Error: path contained symlinks.
RelatedPackageVersions:
 dpkg 1.21.1ubuntu2.1
 apt 2.4.8
SourcePackage: usrmerge
Title: package usrmerge 25ubuntu2 failed to install/upgrade: installed usrmerge package post-installation script subprocess returned error exit status 255
UpgradeStatus: Upgraded to jammy on 2022-12-26 (0 days ago)