Comment 8 for bug 1930573

Thank you Brian for accepting it into hirsute-proposed!

I've tested usrmerge 24ubuntu3.1 from hirsute-proposed, all good:

$ lxc launch ubuntu:bionic usrmerge
$ lxc exec usrmerge bash
# do-release-upgrade
[...]
# reboot
# ls -la /
total 96
drwxr-xr-x 22 root root 4096 Oct 21 15:54 .
drwxr-xr-x 22 root root 4096 Oct 21 15:54 ..
drwxr-xr-x 2 root root 12288 Oct 27 13:11 bin
drwxr-xr-x 2 root root 4096 Oct 21 15:54 boot
drwxr-xr-x 8 root root 500 Oct 27 13:12 dev
drwxr-xr-x 94 root root 12288 Oct 27 13:12 etc
drwxr-xr-x 3 root root 4096 Oct 27 13:03 home
drwxr-xr-x 21 root root 4096 Oct 27 13:08 lib
drwxr-xr-x 2 root root 4096 Oct 27 13:05 lib64
drwxr-xr-x 2 root root 4096 Oct 21 15:48 media
drwxr-xr-x 2 root root 4096 Oct 21 15:48 mnt
drwxr-xr-x 2 root root 4096 Oct 21 15:48 opt
dr-xr-xr-x 502 nobody nogroup 0 Oct 27 13:12 proc
drwx------ 4 root root 4096 Oct 27 13:12 root
drwxr-xr-x 22 root root 700 Oct 27 13:12 run
drwxr-xr-x 2 root root 12288 Oct 27 13:11 sbin
drwxr-xr-x 6 root root 4096 Oct 27 13:08 snap
drwxr-xr-x 2 root root 4096 Oct 21 15:48 srv
dr-xr-xr-x 13 nobody nogroup 0 Oct 27 13:12 sys
drwxrwxrwt 11 root root 4096 Oct 27 13:12 tmp
drwxr-xr-x 12 root root 4096 Oct 27 13:07 usr
drwxr-xr-x 13 root root 4096 Oct 21 15:52 var
# mkdir -p /usr/lib/udev && cp /lib/udev/hwdb.bin /usr/lib/udev/
# sed -i 's/Prompt=lts/Prompt=normal/' /etc/update-manager/release-upgrades
# do-release-upgrade
[...]
Errors were encountered while processing:
 usrmerge
Exception during pm.DoInstall(): E:Sub-process /usr/bin/dpkg returned an error code (1)

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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 (24ubuntu3) ...
ionice: ioprio_set failed: Operation not permitted
chrt: failed to set pid 44214's policy: Operation not permitted

FATAL ERROR:
Both /lib/udev/hwdb.bin and /usr/lib/udev/hwdb.bin exist.

You can try correcting the errors reported and running again
/usr/lib/usrmerge/convert-usrmerge until it will complete without errors.
Do not install or update other Debian packages until the program
has been run successfully.

dpkg: error processing package usrmerge (--configure):
 installed usrmerge package post-installation script subprocess returned error exit status 1
Errors were encountered while processing:
 usrmerge

Upgrade complete

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

To continue please press [ENTER]
=> [C] [ENTER] [x]
# /usr/lib/usrmerge/convert-usrmerge
ionice: ioprio_set failed: Operation not permitted
chrt: failed to set pid 44233's policy: Operation not permitted

FATAL ERROR:
Both /lib/udev/hwdb.bin and /usr/lib/udev/hwdb.bin exist.

You can try correcting the errors reported and running again
/usr/lib/usrmerge/convert-usrmerge until it will complete without errors.
Do not install or update other Debian packages until the program
has been run successfully.

# echo $?
1
# wget https://launchpad.net/ubuntu/+archive/primary/+files/usrmerge_24ubuntu3.1_all.deb
# dpkg -i usrmerge_24ubuntu3.1_all.deb
(Reading database ... 35984 files and directories currently installed.)
Preparing to unpack usrmerge_24ubuntu3.1_all.deb ...
Unpacking usrmerge (24ubuntu3.1) over (24ubuntu3) ...
Setting up usrmerge (24ubuntu3.1) ...
Smartmatch is experimental at /usr/lib/usrmerge/convert-usrmerge line 172.
ionice: ioprio_set failed: Operation not permitted
chrt: failed to set pid 44276's policy: Operation not permitted
The system has been successfully converted.
# /usr/lib/usrmerge/convert-usrmerge
Smartmatch is experimental at /usr/lib/usrmerge/convert-usrmerge line 172.
ionice: ioprio_set failed: Operation not permitted
chrt: failed to set pid 44423's policy: Operation not permitted
The system has been successfully converted.
# echo $?
0
# /usr/lib/usrmerge/convert-usrmerge
Smartmatch is experimental at /usr/lib/usrmerge/convert-usrmerge line 172.
ionice: ioprio_set failed: Operation not permitted
chrt: failed to set pid 44812's policy: Operation not permitted
The system has been successfully converted.
# echo $?
0