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