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I have VirtualBox 6.1 running on Windows 10. It is running virtual machine with Ubuntu server 18.04 LTS. It can work couple of weeks without any issues, but sometimes VM completely looses network. It is not available to connect to (using ssh like putty) and services, which are running in VM also cannot connect to anything (cannot send email, resolve DNS). The VM itself is running, I can control it using VirtualBox window.

Restart from Ubuntu (shutdown -r now) does not help. After restart it still does not have network. Complete shutdown (shutdown -h now) and then start helps.

What could be wrong? How I can investigate and find the reason of the issue?

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  • What does the VM do? How many resources does it have allocated, especially memory & network? Have you looked into the resource utilization on Linux & Windows when this happens?
    – harrymc
    Aug 28, 2021 at 8:13
  • VM running ubuntu server (no GUI). 3Gb of RAM, Network as Bridged adapter, Promiscuous Mode: Deny. Have not looked into resource utilization. On the host (Windows) I have 16 Gb of RAM and there should not be any issues. On Ubuntu, not sure how to make it as when it happens I cannot connect to it.
    – Index
    Aug 30, 2021 at 8:14
  • Could this be associated with some auto-update of Ubuntu? To check: tail /var/log/apt/history.log.
    – harrymc
    Aug 30, 2021 at 8:31
  • What's the error you get from the applications? (No route to host, Connection timed out, ...)
    – golimar
    Sep 2, 2021 at 8:40

2 Answers 2

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In my experience Windows can occasionally hang network devices(/connections) during sleep, or power reduction cycles, if you make no other changes but to reboot the Ubuntu server you may be looking for an issue outside of VirtualBox/Ubuntu directly into the mirky world of drivers, etc.

It is possible that changing your power management settings in BIOS, or Win/VB/Lin to not allow sleep states, or reduced C-states, might alleviate the problem. Unfortunately there are many C-states and this may not be the underlying cause, it would take time (you said weeks) to test. I have had plenty of experience with this on field laptops with similar symptoms, and on post-Haswell CPU; laptops enter lower C-states more predictably.

Just a thought.

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  • Important thing to note that just VM reboot does not help. It should be cold start (complete shutdown and then start). It could be related to VirtualBox
    – Index
    Aug 31, 2021 at 8:16
  • "Put the computer on sleep" settings in Windows is "Never"
    – Index
    Aug 31, 2021 at 10:36
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I would look for problem in DHCP lease. Does it have enough time? Maybe it does not lease again the IP address?

First of all you should look into /var/log/syslog for any errors and network related issues.

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  • How to check that DHCP things?
    – Index
    Aug 30, 2021 at 8:18
  • @Index DHCP is provided by server in local network or the router itself.
    – pbies
    Aug 30, 2021 at 9:22
  • In my case it is router. Just thought there is a way to check that there are issues with DHCP. I do not think there are any issues with DHCP as IP was leased from the beginning and router each time gives same IP address to that VM (linked to MAC address). Additional point is that after restart network does not appear. Only complete VM shutdown and then start helps.
    – Index
    Aug 31, 2021 at 8:13
  • @Index ok, so check both: /var/log/syslog and Windows Event Viewer for issues.
    – pbies
    Aug 31, 2021 at 11:34

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