Original: https://forum.openmediavault.org/index.php?thread/42340-is-there-a-guide-to-in-place-upgrade/&postID=305564#post305564

1. Backup the OS drive (this is allways a good idea, not only for upgrades)
2. Make sure, you have enough free space on your os drive
3. Check any installed plugins if they have been ported to OMV6
   If you are using plugins which have not been / will not be ported, get rid of the plugins except unionfs / mergefolderfs. These two will automatically be be converted to the newer mergerfs plugin
   (Many plugins can be replaced by docker containers. Do this before upgrading)
4. If you installed software from foreign repos make sure they have a release for bullseye or remove the repos / software
5. Go to the cli (Putty, ssh, keyboard) and run these commands (In case of errors stop and ask on the forum before makingthings worse)
   1. Make sure your current install is correct all configs can be deployed by running sudo omv-salt stage run deploy
   2. Get the current install up to date: sudo omv-upgrade
   3. Do the release upgrade by running sudo omv-release-upgrade
      If you see an error message from patch which says a patch has alredy been applied, ignore it. (this is the only error to be ignored)
6. Wait for the last script to finish and reboot.
7. Refresh/clear browser cache (Crtl-Shift R on most browsers)
8. Check if all services and docker containers are running as you expect.
9. If you see Linux image Updates you can not install on the UI, go to the cli and run omv-upgrade once more.

Troubleshooting

If no plugins are visible try to run these commands:

rm -f /usr/sbin/omv-mkaptidx

dpkg-divert --remove --rename /usr/sbin/omv-mkaptidx

omv-mkaptidx