title: sshd preauth child terminated by signal 31
body: <p>I upgraded to ubuntu 18.04 the other day, and since then I can't ssh to my machine again. The auth.log tells me this:</p>
  
  <pre><code>Jan 15 08:41:15 pc207 sshd[5358]: Accepted publickey for oscar from 10.60.0.15 port 42004 ssh2: RSA SHA256:59dtkmxMKMJG22+SQEoo7D55JSr+xlFjRyLMclLY210
  Jan 15 08:41:15 pc207 sshd[5358]: debug1: monitor_child_preauth: oscar has been authenticated by privileged process
  Jan 15 08:41:16 pc207 sshd[5358]: debug1: monitor_read_log: child log fd closed
  Jan 15 08:41:16 pc207 sshd[5358]: fatal: privsep_preauth: preauth child terminated by signal 31
  </code></pre>
  
  <p>While <code>ssh -vvv localhost</code> tells me this:</p>
  
  <pre><code>debug1: Authentication succeeded (publickey).
  Authenticated to localhost ([127.0.0.1]:22).
  debug1: channel 0: new [client-session]
  debug3: ssh_session2_open: channel_new: 0
  debug2: channel 0: send open
  debug3: send packet: type 90
  debug1: Requesting no-more-sessions@openssh.com
  debug3: send packet: type 80
  debug1: Entering interactive session.
  debug1: pledge: network
  debug3: send packet: type 1
  packet_write_wait: Connection to 127.0.0.1 port 22: Broken pipe
  </code></pre>
  
  <p>Google tells me to set <code>UsePrivilegeSeparation</code> to either <code>yes</code>, <code>no</code> or <code>sandbox</code>, but it does nothing. My <code>/etc/ssh/sshd</code> is unmodified.</p>
  
  <p><strong>EDIT:</strong> I upgraded my personal laptop to 18.04 as well (HP Elitebook 8570w, totally unrelated to above stationary Dell) and the exact same error is occurring when I try to ssh to my laptop; preauth child terminated by signal 31.</p>