Apt errors after upgrading

Good morning,

this is my very first post thanks to the fact that I installed OMV about an year ago (4.x) and it always worked fine, but now I have an issue.

I'm using OMV primarily as an Ftp server (almost exclusively), it is installed on a virtual machine on a Qnap Nas (I used the provided iso) and I usually update it connecting via SSH with Putty with the following lines:

# apt update

# apt upgrade

# apt autoclean

#apt autoremove

When I noticed that the 5.x version was available I did:

# apt update

# apt dist-upgrade

rebooted and did my usual update routine.

Now the problem, after dist-upgrading, apt is unable to resolve deb.debian.org.

I tried several times to modify the /etc/apt/sources.list file, appending to every line a different distro name (stable, stretch, buster) or changing the mirror (http://ftp.us.debian.org, ftp.debian.org, ftp.it.debian.org...), trying the update routine for every change, but still I get the error.

I have no problems with the users and folders created before the update, but now I receive several errors creating new users and granting them rights using the interface.

Is there a way to address the issue?

If not, can I save my existing users, folders and data to format the machine and create a new one?

Thank a lot in advance, kind regards

Thank you

Your answer is making me thinking about one thing:

the OMV virtual machine is behind a Nat.

Behind the same Nat there is an internal domain but OMV is not in there (in the domain, I mean).

Could it be possible that OMV is pointing the same DNS as the workstations inside the domain?

Tomorrow morning I'll see...

Do you have an answer for the second question?

Can I back-up users, directories and data from an old OMV and restore/import them in a fresh install?

This way I can by-pass any system related upgrading issue and start again from a blank/fresh system.

Thank you very much,

I did a check with my colleagues, I have to recreate only 2 users, so the job is easy.

I destroyed the old virtual machine and created a new one, but I'm struggling assigning the ip address in a ststic way.

The modem/nat is configured as dhcp server, but I reserved the ip I need for the mac address of the virtual machine.

At this point I installed OMV in the virtual machine, it went fine but configured the network by dhcp and assigned a different ipv4 address.

In order to assign the right ip I modified the /etc/network/interfaces file and created /etc/systemd/static.network file the way suggested on the Debian guide, so now they behave in the same manner (old and new network configuration files) but still I receive a wrong ip address.

How can I modify this behavior?

Thank you very much.

I resorted using omv-firstaid, now the ipv4 is the correct one (but before configuring the net with it I deleted /etc/systemd/static.network).

Just for my curiosity/learning, what does omv-firstaid do?