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

[Gustavo Lopes]

When networking is hung, stopping ssh.service will also resolve the
hang, but reloading or restating ssh.service will hang as well. There
are no problems restarting or reloading ssh.service in other
circumstances.

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Title:
  systemctl restart networking hangs reloading ssh.service

Status in ifupdown package in Ubuntu:
  New

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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