Very strange. Surprisingly, the simple re-installation did do the trick. Luckily, `openssh-server' package doesn't have any hard dependencies to the essential distro meta packages.
Well, originally, I was going to lock the version from `security' repo but first I would have to remove the package anyway, so: $ sudo apt-get remove openssh-server Reading package lists... Done Building dependency tree Reading state information... Done The following packages were automatically installed and are no longer required: libssl1.0.0:i386 openssh-sftp-server Use 'sudo apt autoremove' to remove them. The following packages will be REMOVED: openssh-server 0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded. 1 not fully installed or removed. After this operation, 904 kB disk space will be freed. Do you want to continue? [Y/n] Y (Reading database ... 357805 files and directories currently installed.) Removing openssh-server (1:7.2p2-4ubuntu2.9) ... Processing triggers for man-db (2.7.5-1) ... $ sudo apt-get -y autoremove Reading package lists... Done Building dependency tree Reading state information... Done The following packages will be REMOVED: libssl1.0.0:i386 openssh-sftp-server 0 upgraded, 0 newly installed, 2 to remove and 0 not upgraded. After this operation, 3,223 kB disk space will be freed. (Reading database ... 357792 files and directories currently installed.) Removing libssl1.0.0:i386 (1.0.2g-1ubuntu4.15) ... Removing openssh-sftp-server (1:7.2p2-4ubuntu2.9) ... Processing triggers for libc-bin (2.23-0ubuntu11) ... Processing triggers for man-db (2.7.5-1) ... $ sudo apt-get install openssh-server Reading package lists... Done Building dependency tree Reading state information... Done The following additional packages will be installed: openssh-sftp-server Suggested packages: ssh-askpass rssh molly-guard monkeysphere Recommended packages: ncurses-term ssh-import-id The following NEW packages will be installed: openssh-server openssh-sftp-server 0 upgraded, 2 newly installed, 0 to remove and 0 not upgraded. Need to get 0 B/374 kB of archives. After this operation, 1,013 kB of additional disk space will be used. Do you want to continue? [Y/n] Y Preconfiguring packages ... Selecting previously unselected package openssh-sftp-server. (Reading database ... 357773 files and directories currently installed.) Preparing to unpack .../openssh-sftp-server_1%3a7.2p2-4ubuntu2.9_amd64.deb ... Unpacking openssh-sftp-server (1:7.2p2-4ubuntu2.9) ... Selecting previously unselected package openssh-server. Preparing to unpack .../openssh-server_1%3a7.2p2-4ubuntu2.9_amd64.deb ... Unpacking openssh-server (1:7.2p2-4ubuntu2.9) ... Processing triggers for man-db (2.7.5-1) ... Processing triggers for ureadahead (0.100.0-19.1) ... ureadahead will be reprofiled on next reboot Processing triggers for ufw (0.35-0ubuntu2) ... Processing triggers for systemd (229-4ubuntu21.27) ... Setting up openssh-sftp-server (1:7.2p2-4ubuntu2.9) ... Setting up openssh-server (1:7.2p2-4ubuntu2.9) ... $ sudo systemctl status sshd.service ● ssh.service - OpenBSD Secure Shell server Loaded: loaded (/lib/systemd/system/ssh.service; enabled; vendor preset: enabled) Active: active (running) since Thu 2020-04-23 18:07:13 MSK; 13s ago Process: 27871 ExecStartPre=/usr/sbin/sshd -t (code=exited, status=0/SUCCESS) Main PID: 27874 (sshd) CGroup: /system.slice/ssh.service ├─ 9759 sshd: ia [priv] ├─ 9771 sshd: ia@pts/18 ├─ 9772 -zsh └─27874 /usr/sbin/sshd -D Apr 23 18:07:13 asrockZ97e systemd[1]: Starting OpenBSD Secure Shell server... Apr 23 18:07:13 asrockZ97e sshd[27874]: Server listening on 0.0.0.0 port 22. Apr 23 18:07:13 asrockZ97e sshd[27874]: Server listening on :: port 22. Apr 23 18:07:13 asrockZ97e systemd[1]: Started OpenBSD Secure Shell server. $ ** Changed in: openssh (Ubuntu) Status: New => Invalid -- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to openssh in Ubuntu. https://bugs.launchpad.net/bugs/1874455 Title: ssh daemon doesn't report successful start state to systemd after upgrade to 1:7.2p2-4ubuntu2.9 Status in openssh package in Ubuntu: Invalid Bug description: System info: $ lsb_release -rd Description: Ubuntu 16.04.6 LTS Release: 16.04 $ apt-cache policy openssh-server openssh-server: Installed: 1:7.2p2-4ubuntu2.9 Candidate: 1:7.2p2-4ubuntu2.9 Version table: *** 1:7.2p2-4ubuntu2.9 500 500 https://mirror.one.com/ubuntu xenial-proposed/main amd64 Packages 100 /var/lib/dpkg/status 1:7.2p2-4ubuntu2.8 500 500 https://mirror.one.com/ubuntu xenial-security/main amd64 Packages 500 https://mirror.one.com/ubuntu xenial-updates/main amd64 Packages 500 http://us.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages 1:7.2p2-4 500 500 https://mirror.one.com/ubuntu xenial/main amd64 Packages 500 http://us.archive.ubuntu.com/ubuntu xenial/main amd64 Packages - what should happen? After regular update ssh daemon should restart successfully. - what actually happens: $ sudo apt-get -y update [skip] Fetched 2,473 B in 1s (1,702 B/s) Reading package lists... Done $ sudo apt-get -y dist-upgrade Reading package lists... Done Building dependency tree Reading state information... Done Calculating upgrade... Done The following packages were automatically installed and are no longer required: linux-headers-4.4.0-164 linux-headers-4.4.0-164-generic linux-image-4.4.0-164-generic linux-modules-4.4.0-164-generic linux-modules-extra-4.4.0-164-generic Use 'sudo apt autoremove' to remove them. 0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded. 1 not fully installed or removed. After this operation, 0 B of additional disk space will be used. Setting up openssh-server (1:7.2p2-4ubuntu2.9) ... Job for ssh.service failed because a timeout was exceeded. See "systemctl status ssh.service" and "journalctl -xe" for details. invoke-rc.d: initscript ssh, action "restart" failed. ● ssh.service - OpenBSD Secure Shell server Loaded: loaded (/lib/systemd/system/ssh.service; enabled; vendor preset: enabled) Active: activating (auto-restart) (Result: timeout) since Thu 2020-04-23 17:21:42 MSK; 3ms ago Process: 9000 ExecStart=/usr/sbin/sshd -D $SSHD_OPTS (code=exited, status=0/SUCCESS) Process: 8996 ExecStartPre=/usr/sbin/sshd -t (code=exited, status=0/SUCCESS) Main PID: 9000 (code=exited, status=0/SUCCESS) Apr 23 17:21:42 asrockZ97e systemd[1]: Failed to start OpenBSD Secure Shell server. Apr 23 17:21:42 asrockZ97e systemd[1]: ssh.service: Unit entered failed state. Apr 23 17:21:42 asrockZ97e systemd[1]: ssh.service: Failed with result 'timeout'. dpkg: error processing package openssh-server (--configure): subprocess installed post-installation script returned error exit status 1 Errors were encountered while processing: openssh-server E: Sub-process /usr/bin/dpkg returned an error code (1) However, if I check manually then everything seems fine: $ ps aux | grep sshd | grep -v grep root 9481 0.0 0.0 26212 3728 ? Ss 17:23 0:00 /usr/sbin/sshd -D $ sudo systemctl status sshd.service ● ssh.service - OpenBSD Secure Shell server Loaded: loaded (/lib/systemd/system/ssh.service; enabled; vendor preset: enabled) Active: activating (start) since Thu 2020-04-23 17:29:15 MSK; 1min 19s ago Process: 10454 ExecStartPre=/usr/sbin/sshd -t (code=exited, status=0/SUCCESS) Main PID: 10457 (sshd) CGroup: /system.slice/ssh.service ├─ 9759 sshd: ia [priv] ├─ 9771 sshd: ia@pts/18 ├─ 9772 -zsh ├─10457 /usr/sbin/sshd -D ├─10750 sudo systemctl status sshd.service └─10760 systemctl status sshd.service Apr 23 17:29:15 asrockZ97e systemd[1]: Starting OpenBSD Secure Shell server... Apr 23 17:29:15 asrockZ97e sshd[10457]: Set /proc/self/oom_score_adj from 0 to -1000 Apr 23 17:29:15 asrockZ97e sshd[10457]: Server listening on 0.0.0.0 port 22. Apr 23 17:29:15 asrockZ97e sshd[10457]: Server listening on :: port 22. Apr 23 17:30:34 asrockZ97e sudo[10750]: ia : TTY=pts/18 ; PWD=/home/ia ; USER=root ; COMMAND=/bin/systemctl status sshd.service Apr 23 17:30:34 asrockZ97e sudo[10750]: pam_unix(sudo:session): session opened for user root by ia(uid=0) $ ssh localhost Last login: Thu Apr 23 17:01:34 2020 $ After some google fu, I found some recommendations about removing `-D' from `ExecStart' and replacing `Type=notify' by `Type=forking' in `/etc/systemd/system/sshd.service' but I'm not sure how accurate those hints are and what the real root cause behind such sudden and unexpected change in behavior. P.S. I do realize that I use the package from `proposed' repo but I don't think that it's the excuse for a such strange behavior after upgrade. 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