I've got a buster VM (upgraded from stretch) which does not launch sshd (and Unbound) until a login attempt happens on a TTY. (An unsuccessful attempt appears to be enough.)
At that point, both sshd and Unbound start successfully, and network login is possible. I don't think I have changed the service configuration. There is nothing unusual about the networking setup, except that it doesn't use DHCP, and there is a static stanza in /etc/network/interfaces, with a matching auto directive. ● ssh.service - OpenBSD Secure Shell server Loaded: loaded (/lib/systemd/system/ssh.service; enabled; vendor preset: enab Active: active (running) since Sat 2019-05-04 17:47:31 UTC; 8min ago Docs: man:sshd(8) man:sshd_config(5) Process: 684 ExecStartPre=/usr/sbin/sshd -t (code=exited, status=0/SUCCESS) Main PID: 694 (sshd) Tasks: 1 (limit: 1149) Memory: 3.1M CGroup: /system.slice/ssh.service └─694 /usr/sbin/sshd -D May 04 17:46:20 storage1 systemd[1]: Starting OpenBSD Secure Shell server... May 04 17:47:31 storage1 sshd[694]: Server listening on 0.0.0.0 port 22. May 04 17:47:31 storage1 sshd[694]: Server listening on :: port 22. May 04 17:47:31 storage1 systemd[1]: Started OpenBSD Secure Shell server. May 04 17:48:04 storage1 sshd[708]: Accepted publickey for fw from 172.17.151.1 May 04 17:48:04 storage1 sshd[708]: pam_unix(sshd:session): session opened for u ● unbound.service - Unbound DNS server Loaded: loaded (/lib/systemd/system/unbound.service; enabled; vendor preset: Active: active (running) since Sat 2019-05-04 17:47:32 UTC; 9min ago Docs: man:unbound(8) Process: 683 ExecStartPre=/usr/lib/unbound/package-helper chroot_setup (code=e Process: 687 ExecStartPre=/usr/lib/unbound/package-helper root_trust_anchor_up Main PID: 695 (unbound) Tasks: 1 (limit: 1149) Memory: 8.0M CGroup: /system.slice/unbound.service └─695 /usr/sbin/unbound -d May 04 17:46:20 storage1 systemd[1]: Starting Unbound DNS server... May 04 17:47:32 storage1 package-helper[687]: /var/lib/unbound/root.key has cont May 04 17:47:32 storage1 package-helper[687]: success: the anchor is ok May 04 17:47:32 storage1 unbound[695]: [695:0] notice: init module 0: subnet May 04 17:47:32 storage1 unbound[695]: [695:0] notice: init module 1: validator May 04 17:47:32 storage1 unbound[695]: [695:0] notice: init module 2: iterator May 04 17:47:32 storage1 unbound[695]: [695:0] info: start of service (unbound 1 May 04 17:47:32 storage1 systemd[1]: Started Unbound DNS server. As far as I can tell, the system reaches multi-user.target successfully, at which point I expect that sshd.service can start as well: ● multi-user.target - Multi-User System Loaded: loaded (/lib/systemd/system/multi-user.target; static; vendor preset: Active: active since Sat 2019-05-04 17:34:16 UTC; 22min ago Docs: man:systemd.special(7) May 04 17:34:16 storage1 systemd[1]: Reached target Multi-User System. Any suggestions how to debug this further? I don't think this happened with Debian stretch.