On a test OMV 4.x system with the flashmemory plugin installed, this is all I did to upgrade it to OMV 5.x (as root):

I changed this to a script (no changes but eliminates the cut&paste issues:

wget -O - https://github.com/OpenMediaVault-Plugin-Developers/installScript/raw/master/upgrade4to5 | sudo bash

reboot

apt-get purge openmediavault-omvextrasorg resolvconf
wget -O - https://github.com/OpenMediaVault-Plugin-Developers/packages/raw/master/install | bash
apt-get update
apt-get dist-upgrade

omv-salt deploy run nginx

omv-salt deploy run phpfpm

apt-get install usrmerge

omv-confdbadm migrate conf 5.0.0

Clear your browser cache after upgrading!

omv 5.5.21 usul | 64 bit | 5.4 proxmox kernel | omvextrasorg 5.4.2
omv-extras.org plugins source code and issue tracker - github

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