[CentOS] systemctl reboot -- server not accessible after reboot

Sat Oct 14 22:24:03 UTC 2017
Jonathan Billings <billings at negate.org>

On Oct 14, 2017, at 1:54 PM, Mike <1100100 at gmail.com> wrote:
> Server disconnects my ssh connection and never comes back up.
> Go to the server and the power is on but the server is not accessible by ssh.
> When I connect a monitor and keyboard --- non-responsive.  It's like
> it's in suspend mode.
> I push and hold the power button until the server fully powers down.
> Push power again and everything boots, goes to prompt, and all is well.

When you say that the monitor is plugged in, and the server is unresponsive, does that mean that the monitor doesn’t even come active?  That sounds like it might have crashed the kernel in a way that the display isn’t showing.

You could set up kdump to catch that.  You could also set up a persistent journal (create /var/log/journal) and try again, then when you manually power it up, check to see if anything was logged in the journal.

If the system’s keyboard is plugged in, you could try using the magic sysrq keys to get it to do something.  (see https://en.wikipedia.org/wiki/Magic_SysRq_key )
Try ‘c’ to initiate a crashdump to force kdump to record a kernel dump, then you can examine the active processes.  ‘k’ or ‘g’ might clean up the display if it’s bad.  

Also, remote syslog is always helpful for these kinds of situations, although if the network is down when it crashes then it won’t be as helpful, which is why I suggest looking at the journal.

Jonathan Billings <billings at negate.org>