title: Reboot and poweroff 'destructive' on Ubuntu 16.04
body: <p>When I try to reboot or turn off my laptop, it doesn't work. After investigating a little further:</p>
  
  <pre><code>$ systemctl status reboot.target
  ● reboot.target - Reboot
     Loaded: loaded (/lib/systemd/system/reboot.target; disabled; vendor preset: disabled)
     Active: inactive (dead)
       Docs: man:systemd.special(7)
  </code></pre>
  
  <p>reboot is disabled. However, trying to enable it with <code>systemctl enable reboot.target</code> results in this output:
  <code>Failed to execute operation: File exists</code></p>
  
  <p>After running <code>reboot</code>, I get the following error:</p>
  
  <pre><code>Failed to start reboot.target: Transaction is destructive.
  See system logs and 'systemctl status reboot.target' for details.
  </code></pre>
  
  <p>I have no idea what to do; for now I'll just force poweroff, but I'd like to be able to use the reboot and shutdown functionality without cutting power every time I want to turn it off.</p>