Server won't reboot after installing NetworkManager and configuring Wireguard

Bare Metal and VPS
1

Hello

I had a KimSuffi server that was working fine, until I thought it would be a good idea to:

  1. install NetworkManager, which would have been useful for (2)
  2. import a Wireguard configuration with nmcli (apparently perfectly correct)
  3. reboot

Additionally I had enabled ufw, which allowed SSH access with a key.

Since the reboot I can no longer SSH or even reach it with ping.

I don't see anything obvious in syslog apart from the following, which I don't understand the reason for:
2026-07-30T13:41:03.310271+00:00 ns539605 kernel: [UFW BLOCK] IN=eno3 OUT= MAC=0c:c4:7a:9a:de:da:00:ff:ff:ff:ff:fd:08:00 SRC=[my client ip] DST=[my server] LEN=176 TOS=0x00 PREC=0x00 TTL=49 ID=3574 PROTO=UDP SPT=51820 DPT=37393 LEN=156
2026-07-30T13:41:04.213989+00:00 ns539605 systemd[1]: systemd-fsckd.service: Deactivated successfully.

I can reboot in rescue mode, but how can I undo what I did afterwards? How to uninstall?

And incidentally, why does this prevent the server from being reachable... (but it's not urgent...)

Thanks for your help!

2

Hello @MartinR2

You have installed NetworkManager on a server that, by default, managed the network with the traditional system (ifupdown) :roll_eyes:

Let's try to fix it.

  1. Boot the server in rescue mode from the client area.
  2. Access your server via SSH in rescue mode.
  3. Mount your filesystem :right_arrow: The server's disk does not mount automatically in rescue mode, but it is visible. First, locate your root partition. You can list the partitions with lsblk. Then mount it to a folder, for example:
    mount /dev/sda1 /mnt
  4. Access the mounted filesystem to undo the changes
    chroot /mnt
  5. Disable UFW to regain SSH access
    ufww disable
  6. Uninstall NetworkManager to revert to the classic network setup
    apt remove network-manager
  7. Restore the manual network configuration. It's possible that uninstalling NetworkManager removed the previous configuration in /etc/network/interfaces.
  8. Exit the chroot environment and reboot
    exit
    reboot

Make sure the server boots from the hard drive in the Netboot settings of the client area :wink:

I hope this helped, cheers.
Sergio Turpín

3

A big thank you, my server is working fine now!

Do you know if I can import a WireGuard network interface without NetworkManager, probably using ifupdown, and how?

4

As soon as I reactivate ufw and the server is rebooted, we can no longer access it.

Before my attempt to install network‑manager, with the same ufw configuration, it worked fine.

Why can I no longer enable ufw?

The firewall configuration is:

root@rescue12-customer-ca:/# ufw status
Status: active

To Action From

22 ALLOW Anywhere
80 ALLOW Anywhere
443 ALLOW Anywhere
3306/tcp ALLOW xxx.xxx.xxx.xxx [the address of a client I want to allow]
3306/tcp ALLOW 127.0.0.1