It turns out Docker wasn't necessary. apt --fix-broken install solved my problem.
I started looking into Docker which is interesting but confusing. I've not been able to find a howto or guide which explains Docker in OMV from the basics. If there is such a guide, please point me to it.
Also: I've got logitechmediaserver (Squeezebox) installed the usual debian-way (apt-get install). Is this likely to be an issue when upgrading?
It turns out that logitechmediaserver requires libio-socket-ssl-perl which apparently isn't in Debian 9 and I've not found an obvious way of installing libio-socket-ssl-perl. That's something I need to figure out before I upgrade my main system. I'd be grateful for suggestions of how I solve this.
Don't wait for OMV 3.x plugins that have not been ported to OMV 4.x. Many will never be ported. The Downloaders section was particularly hard hit.
The general consensus seem to be that Dockers are going to replace plugins in many cases. So just go with Dockers.
I did the upgrade on a reserve system and it appeared to work great. I'll upgrade my main system as well once I've done a little bit more testing.
I'm not yet familiar with Dockers, but I'll look into that.
Thanks! I'll add those then.
I've read the information stating that plugins not available in 4.x needs to be uninstalled, but would appreciate if someone could confirm my selection. From what I can tell, my 3.x system has the following plugins (Y means available in 4.x, N means not available i 4.x, X = part of OMV-extras):
Y transmission
Y minidlna
Y plexmediaserver
Y locate
Y omv-extras
N couchpotato X
N sonarr X
N forkeddaapd
N shairport
Is it correct that the bottom four are not available in 4.x? Of those I can manage fine without 3 of 4, but will miss Couchpotato. Are the plugins not available in 4.x now (such as couchpotato) likely to become available in 4.x anytime soon? Or the frame the questions differently, will I be better off waiting a few weeks before I upgrade?
Also: I've got logitechmediaserver (Squeezebox) installed the usual debian-way (apt-get install). Is this likely to be an issue when upgrading?
Zitat von tkaiserSimilar error message and same card: Suddenly OMV 3 needs 5 mins to boot
Yeah, that might exactly my problem.
While I've been posting the system has eventually booted and I can finally access the web interface. Thread solve, I suppose, although to summarize for future readers. Double and triple check you network cables. That was the only real problem in this thread. Thanks for all help 
It turned out to be a disconnected network cable somewhere in between the router and the server. I've successfully connected to the network now, however I've now got an issue where the system appears to be stuck during boot at:
Started Update UTMP about System Boot/Shutdown
I don't know if my attempt at trouble shooting has caused the problem.
I managed to boot into recovery mode. The server was assigned the appropriate IP, I could ping external sites, but I could not access the OMV web interface. In normal mode, however, it appears to be stuck at Started Update UTMP about System Boot/Shutdown. I've not found any threads which has helped med solve this problem...
lspci shows among other things
...
00:1c.0 PCI bridge: Intel ..
00:1c.2 PCI bridge: Intel ..
00:1c.3 PCI bridge: Intel ..
...
02:00.0 Ethernet Controller: Realtek Semiconductor ...
03:00.0 PCI Bridge: ASMedia ...
Two side notes.
1.
During boot I receive an error saying
[FAILED] Failed to start Enable File System Quatos
However, from what I gather by reading the forum this is unrelated to my network issues.
2.
I've got a realtek rtl8111/8168/8411 pci express ethernet card. There have been issues with this card on Linux, however since I've got a system which have worked for a long time I belive it is unlikely that this is the source of my problem. Or is it likely that an upgrade of OMV have caused problems? (I've not done an upgrade during the last few weeks, though.)
Yeah,
The first time i tried omv-firstaid I received (this might have been in recovery mode):
ERROR: [Errno 2] No such file or directory.
The second time I received:
Error: Failed to execute command 'export PATH=/bin:/sbin:/usr/bin: ... export LANG=C monit monitor collectd 2>&1' with exit cod '1': Cannot create socket to [localhost]:2812 -- Cannot assign requested address
My OMV v.3 has suddenly lost Internet access. I've connected a monitor and keyboard to troubleshoot. As I can't copy and paste terminal output I'll rewrite here what I belive is essential info and output and would greatly appreciate some help solving this.
root@omv: ifconfig
Eth0 Link encap: Ethernet HWaddr: "mac-address"
...
lo Link encap: Local Loopback
inet addr: 127.0.0.1 Mask: 255.0.0.0
root@omv: ifup eth0
Listing on LPF/eth0/"mac-address"
DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 4
(repeated six times for same port but with different intervals)
No DHCPOFFERS received.
No working leases in persistent database - sleeping.
ifquery: recursion detected for interface eth0 in post-up phase
run-parts: /etc/network/if-up.d/openmediavault-issue exited with return code 1
Failed to bring up eth0
...
Some further trouble shooting. When running omv-firstaid and selecting configure network interface I get the output
ERROR: [Errno 2] No such file or directory.
All other units on the network works as usual hence the router does not appear to be at fault. What do I do?
I've reconnected my router so both servers are now connected with the previously used IP-addresses. Both servers now appear to be working flawlessly.
root@server-which-had-dns-issue:~# cat /etc/resolv.conf
# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
# DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
nameserver 192.168.1.1
search e12b
root@working-server:~# cat /etc/resolv.conf
# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
# DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
nameserver 192.168.1.1
The output of cat /etc/resolv.conf is displayed above, with the exact same setup as in the previous post. The only difference being a different local ip because of a different router. Hence, the DNS-issue is probably still present although not a problem at the moment, but will be when I have to change ip-adressess (which I may have to do in a few months because of a new fiber provider).
What do I do to prevent further problems related to dns?
root@server-with-dns-issue:~# cat /etc/resolv.conf
# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
# DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
nameserver 84.208.20.110
nameserver 84.208.20.111
search e12b getinternet.no
root@e12b-server:~#
root@working-server:~# cat /etc/resolv.conf
# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
# DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
nameserver 84.208.20.110
nameserver 84.208.20.111
search getinternet.no
root@omv-e12b:~#
I spot one difference when comparing my servers, emphasized in bold, in output no one from the top. Is that the cause of my problems? How do I resolve it? In System --> Settings --> General e12b is specified as domain name for both servers.
I've not got access to my server from where I am now so I'm unable to post the output of
cat /etc/resolv.conf
however I've got no doubt this is a DNS-issue. I attempted
dpkg-reconfigure resolvconf
to update /etc/resolv.conf but the settings remained unchanged. I've also tried changing from dhcp to static ip, but it hasn't solved the problem.
Nope 
root@my-server:~# sudo -- sh -c 'apt-get update; apt-get upgrade -y; apt-get dist-upgrade -y; apt-get autoremove -y'
Ign file: InRelease
Ign file: Release.gpg
Ign file: Release
Ign file: Translation-en
46% [Connecting to ftp.no.debian.org] [Connecting to security.debian.org] [Connecting ...
Unable to resolve.
Due to change of router I've become unable to update my system and also have major problems running various services. I've got two servers with similar configurations (probably identical), however I've only got a problem with the new one (my major server, the old one is for testing and playing).
I've got access via the web interface and ssh, however I'm unable to do much of any use, such as accessing logitech mediaserver or plex, or simply do an update.
I've attempted several solutions including disabling extra repositories.
I've also tried dpkg-reconfigure resolvconf as suggested here, but the settings are unchanged after reboot:
System not updating
I've also tried changing from dhcp to static ip.
Any other suggestions? Surely there must be a solution so I can get this excellent software working again.
I'm running version 3.0.64.
I'm planning to install OMV on my server after a great period of testing OMV on old hardware. I've currently got two 3TB disks for storage (plus one SSD for OMV). My question is: Will I be able to add one similar disk to my raid setup at a later time if I set up my system now with a Raid created with two disks?
Assuming it is possible (and easy) to add disks later, are there any important reasons why I should do that investment now rather than postpone it?
Sidenote: The purpose of my OMV is to act as a homeserver for serving music and other home media plus of course backup of all the machines in our house.