[Bug 1991592] Re: openssh-server should ship a systemd generator to generate ssh socket port configuration from sshd_config

[Corey Reichle]

> False. It is documented in the manpage,

I looked in the manpage for my install, and no mention of socket
activation.

I looked in the README.Debian, and it indicated you can switch to socket
activation, over standard daemonization, if you choose, by masking sshd,
and enabling sshd.socket, and starting sshd.socket instead.

Maybe it's in the new release.  I am basing my info on where I
encountered this issue.

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Title:
  openssh-server should ship a systemd generator to generate ssh socket
  port configuration from sshd_config

Status in openssh package in Ubuntu:
  Triaged

Bug description:
  A criticism of the existing sshd socket activation implementation is
  that Port/ListenAddress options are migrated on a one-time basis at
  package upgrade time, and afterwards users get the surprising behavior
  that Port/ListenAddress settings added to sshd_config are ignored.

  A systemd generator could be used to change the ssh socket unit
  configuration on boot, and on each change of /etc/ssh/sshd_config.
  Sample implementation from Dimitri:

  ssh.socket:
  [Unit]
  Wants=sshd-config.path

  #
  # Note the below defaults are cleared and overriden by
  #    /lib/systemd/system-generators/sshd-generator
  # based on the sshd config from the sshd -T output
  #
  ListenStream=[::]:22
  ListenStream=0.0.0.0:22

  diff --git a/systemd/sshd-config.path b/systemd/sshd-config.path
  new file mode 100644
  index 000000000..cfa9674a3
  --- /dev/null
  +++ b/systemd/sshd-config.path
  @@ -0,0 +1,4 @@
  +[Unit]
  +ConditionPathExists=!/etc/ssh/sshd_not_to_be_run
  +[Path]
  +PathChanged=/etc/ssh/sshd_config
  diff --git a/systemd/sshd-config.service b/systemd/sshd-config.service
  new file mode 100644
  index 000000000..b009ea52c
  --- /dev/null
  +++ b/systemd/sshd-config.service
  @@ -0,0 +1,5 @@
  +[Unit]
  +Description=Regenerate ssh.socket.d/ssh-listen.conf drop-in
  +
  +[Service]
  +ExecStart=/bin/systemctl daemon-reload
  diff --git a/systemd/sshd-generator b/systemd/sshd-generator
  new file mode 100755
  index 000000000..72c6aac04
  --- /dev/null
  +++ b/systemd/sshd-generator
  @@ -0,0 +1,10 @@
  +#!/bin/sh
  +set -eu
  +mkdir -p /run/sshd
  +sshd -t
  +mkdir -p $1/ssh.socket.d
  +target="$1/ssh.socket.d/ssh-listen.conf"
  +echo '[Socket]' > $target
  +echo 'ListenStream=' >> $target
  +sshd -T | sed -n 's/^listenaddress /ListenStream=/p' >> $target
  +rmdir --ignore-fail-on-non-empty /run/sshd

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