[Bug 1584393] Re: systemctl restart networking hangs reloading ssh.service

[Dan Watkins]

I've reproduced this on GCE also.  Here's what ssh.service looks like
during the hang (and it looks like the reload hasn't affected it):

$ sudo systemctl status ssh.service
● ssh.service - OpenBSD Secure Shell server
   Loaded: loaded (/lib/systemd/system/ssh.service; enabled; vendor preset: enabled)
   Active: active (running) since Thu 2016-06-23 08:32:11 UTC; 6min ago
  Process: 2702 ExecReload=/bin/kill -HUP $MAINPID (code=exited, status=0/SUCCESS)
 Main PID: 1643 (sshd)
    Tasks: 1
   Memory: 3.8M
      CPU: 108ms
   CGroup: /system.slice/ssh.service
           └─1643 /usr/sbin/sshd -D

Jun 23 08:32:11 xenial-160623-0931 systemd[1]: Started OpenBSD Secure Shell server.
Jun 23 08:32:17 xenial-160623-0931 sshd[1747]: Accepted publickey for ubuntu from 86.179.225.58 port 46404 ssh2: RSA SHA256:HRlolnELGM4aMQXejVDjc0kWktid481/BsLIHtc7Tv0
Jun 23 08:32:17 xenial-160623-0931 sshd[1747]: pam_unix(sshd:session): session opened for user ubuntu by (uid=0)
Jun 23 08:37:17 xenial-160623-0931 systemd[1]: Reloading OpenBSD Secure Shell server.
Jun 23 08:37:17 xenial-160623-0931 sshd[1643]: Received SIGHUP; restarting.
Jun 23 08:37:17 xenial-160623-0931 systemd[1]: Reloaded OpenBSD Secure Shell server.
Jun 23 08:37:17 xenial-160623-0931 sshd[1643]: Server listening on 0.0.0.0 port 22.
Jun 23 08:37:17 xenial-160623-0931 sshd[1643]: Server listening on :: port 22.
Jun 23 08:37:22 xenial-160623-0931 sshd[3134]: Accepted publickey for ubuntu from 86.179.225.58 port 46520 ssh2: RSA SHA256:HRlolnELGM4aMQXejVDjc0kWktid481/BsLIHtc7Tv0
Jun 23 08:37:22 xenial-160623-0931 sshd[3134]: pam_unix(sshd:session): session opened for user ubuntu by (uid=0)

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https://bugs.launchpad.net/bugs/1584393

Title:
  systemctl restart networking hangs reloading ssh.service

Status in ifupdown package in Ubuntu:
  Confirmed

Bug description:
  Issues "systemctl restart networking" never exits. It hangs during a
  call to "systemctl reload ssh.service":

  ● networking.service - Raise network interfaces
     Loaded: loaded (/lib/systemd/system/networking.service; enabled; vendor preset: enabled)
    Drop-In: /run/systemd/generator/networking.service.d
             └─50-insserv.conf-$network.conf
     Active: activating (start) since Sat 2016-05-21 21:41:58 UTC; 18s ago
       Docs: man:interfaces(5)
    Process: 1288 ExecStop=/sbin/ifdown -a --read-environment (code=exited, status=0/SUCCESS)
    Process: 1376 ExecStartPre=/bin/sh -c [ "$CONFIGURE_INTERFACES" != "no" ] && [ -n "$(ifquery --read-environment --list --exclude=lo)" ] &
   Main PID: 1383 (ifup)
      Tasks: 7 (limit: 512)
     Memory: 1.8M
        CPU: 111ms
     CGroup: /system.slice/networking.service
             ├─1383 /sbin/ifup -a --read-environment
             ├─1479 /sbin/dhclient -1 -v -pf /run/dhclient.enp0s3.pid -lf /var/lib/dhcp/dhclient.enp0s3.leases -I -df /var/lib/dhcp/dhclient6
             ├─1480 /bin/sh -c /bin/run-parts --exit-on-error /etc/network/if-up.d
             ├─1481 /bin/run-parts --exit-on-error /etc/network/if-up.d
             ├─1504 /bin/sh /etc/network/if-up.d/openssh-server
             ├─1507 /bin/sh /usr/sbin/invoke-rc.d ssh reload
             └─1527 systemctl reload ssh.service

  Then issuing the same command from another terminal causes the first
  to exit successfully (the second also exists successfully).

  On the official vagrant image, I get this problem independently of
  whether the command is issued through and ssh session. I've gotten the
  same behavior on the official xenial AMIs.

  ProblemType: Bug
  DistroRelease: Ubuntu 16.04
  Package: ifupdown 0.8.10ubuntu1
  ProcVersionSignature: Ubuntu 4.4.0-22.40-generic 4.4.8
  Uname: Linux 4.4.0-22-generic x86_64
  ApportVersion: 2.20.1-0ubuntu2
  Architecture: amd64
  Date: Sat May 21 21:35:08 2016
  ProcEnviron:
   TERM=xterm
   PATH=(custom, no user)
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  SourcePackage: ifupdown
  UpgradeStatus: No upgrade log present (probably fresh install)

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