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While doing a run of the mill apt upgrade, a Tomcat 7 post install script ran with the common A new version of configuration file /etc/default/tomcat7 is available.... Unfortunately, I didn't attend to it quickly enough and the SSH connection was reset. How do I recover from this? Can I reattach to the post install screen? Is it safe to kill it? If I kill it, is there a script somewhere I should be manually executing?

I saw this question about doing an upgrade of OS versions, but either the solution (screen -r) isn't relevant or I'm not using it correctly.

$ screen -r
There is no screen to be resumed.

I can see the process running:

$ ps -a
  PID TTY          TIME CMD
  416 pts/2    00:00:00 frontend
  423 pts/2    00:00:00 tomcat7.postins
  430 pts/2    00:00:00 ucf
  475 pts/2    00:00:00 whiptail
  634 pts/1    00:00:00 ps

As suggested by Dmitry Zayats I've looked at the Tomcat 7 post install script. In my installation of Ubuntu 14.04, it's found here: /var/lib/dpkg/info/tomcat7.postinst

Opening that up, I believe I see the relevant line where I initially lost my connection:

ucf --debconf-ok --sum-file /usr/share/tomcat7/defaults.md5sum $tmpfile $CONFFILE

Community
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Toby Murray
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2 Answers2

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Kill the dpkg/apt session and re-issue the command. It will re-deploy in-progress packages. With most pre/post install scripts it will work out okay. In the few cases where the upgrades packages don't work as expected, reinstall the packages.

And, as the others said: tmux/screen.

John Keates
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Whenever you work on a remote machine (even with stable network connection in enterprise network) the best practice is to use terminal multiplexer for long running and important tasks.
I suggest to invest time and learn how to use screen or tmux, this will increase your productivity and will make those upgrades much safer.
Not only you will be able to reconnect in case connection was lost - but there is so much more.
Like logging your entire session, splitting screens so you can have multiple terminals in same window running on a single ssh connection. Horizontal split / vertical split.

Dmitry Zayats
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