Comment 4 for bug 1818431

Hello Noel, thanks for filing this bug in Ubuntu.

Both Debian and Ubuntu like to install services with a working default configuration, and it is expected that a service is running after it is installed. That's why winbind is started right after it is installed.

During upgrades, the same principle applies: in order to have the new version of the service available after an upgrade, it must be restarted. If the restart fails, it should be investigated.

When you say this:
"""
Ubuntu 18.04 is regression: The `winbind` package breaks APT/DPGK package manager because `/var/lib/dpkg/info/winbind.postinst` is trying to start the service - that's bad regression.
"""

Could you elaborate a bit on which steps you took for the winbind service to fail to run? The logs show it is complaining that it didn't join the domain, or somehow lost the secret.

As an example, I just did the following on a fresh bionic container:

sudo apt update
sudo apt dist-upgrade -y
sudo apt install samba winbind -y

And it worked just fine:
root@bionic-winbind:~# systemctl status winbind
● winbind.service - Samba Winbind Daemon
   Loaded: loaded (/lib/systemd/system/winbind.service; enabled; vendor preset: enabled)
   Active: active (running) since Thu 2019-03-07 20:09:32 UTC; 18s ago
     Docs: man:winbindd(8)
           man:samba(7)
           man:smb.conf(5)
 Main PID: 2793 (winbindd)
   Status: "winbindd: ready to serve connections..."
    Tasks: 4 (limit: 4915)
   CGroup: /system.slice/winbind.service
           ├─2793 /usr/sbin/winbindd --foreground --no-process-group
           ├─2795 /usr/sbin/winbindd --foreground --no-process-group
           ├─2960 /usr/sbin/winbindd --foreground --no-process-group
           └─2961 /usr/sbin/winbindd --foreground --no-process-group

Can you please share your /etc/samba/smb.conf? The logs from /var/log/samba/log* would also help.