[Bug 103436] Re: sshd not reconfigured by /etc/network

[Martin Pitt]

Perry, I just revisited this:

 - /etc/network/if-up.d/openssh-server hack introduces a race (you run
into connection errors after bringing up a new interface as sshd stops
listening briefly while being reloaded).

 - I can't seem to be able to actually reproduce that issue: I can start
a VM with no network interfaces, remove the above hack, then start sshd,
then bring up an ethernet interface, and I can connect to ssh via
ethernet just fine. Also, e. g. Fedora has no counterpart of this hack,
and these days a lot of people would complain if that would cause
problems, as hotpluggable/roaming network devices are everywhere.

 - /etc/network/if-up.d/ isn't being run when using networkd/netplan,
thus in our cloud instances. So far this doesn't seem to have caused any
issues.

So my questions:

  (1) Can you please describe more precisely what exactly you did back
then? Do you have a nonstandard SSH configuration with some
ListenAddresses/AddressFamily restrictions or similar?

  (2) Can you please disable the hack (sudo chmod 0 /etc/network/if-up.d
/openssh-server) and check if your use case works without it?

Thanks!

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https://bugs.launchpad.net/bugs/103436

Title:
  sshd not reconfigured by /etc/network

Status in openssh package in Ubuntu:
  Fix Released

Bug description:
  Binary package hint: openssh-server

  If you have a device that roams a lot (like a laptop), you want
  daemons like sshd to be tweaked/restarted by scripts in /etc/network
  so that they re-open the socket they listen on when the network
  address changes. (Yes, some of us really do want to be able to
  remotely log in to our laptops after we bring them home and they roam
  onto the home WiFi network etc.)

  Right now there is no sshd script in /etc/network/* but it would be
  trivial to create one and add it to the package. For sshd, it would be
  simplest just to restart the daemon.

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