Is it possible to remotely force a reboot on Ubuntu 20.04.3?

[Robert Heller]

At Mon, 21 Feb 2022 20:16:37 +0100 bo.berglund at gmail.com, "Ubuntu user technical support,? not for general discussions" <ubuntu-users at lists.ubuntu.com> wrote:

> 
> On Mon, 21 Feb 2022 13:49:03 -0500 (EST), Robert Heller <heller at deepsoft.com>
> wrote:
> 
> >This isn't the Ubuntu machine.  It is a Raspberry Pi.  And for some reason it 
> >is mapping the bosse user to the pi user...
> 
> The target (aspomint) is an Ubuntu Mint machine with IP 192.168.117.251
> 
> 
> The machine I used to issue the commands from is an RPi4, which still runs fine
> and I can use for testing. It has IP 192.168.117.131
> 
> On the RPi4:
> 
> $ ping aspomint
> PING aspomint (192.168.117.251) 56(84) bytes of data.
> 64 bytes from aspomint (192.168.117.251): icmp_seq=1 ttl=64 time=0.304 ms
> 
> THOUGHTS....
> ------------
> I am kicking myself for not covering this lockup case, though!
> 
> When I taveled there on Feb 9 to set it up I decommisioned a TLink MR600 Mobile
> broadband router, which has been used before the fiber was installed.
> 
> It was powered via a timer set to cut power at night for 1 minute because I had
> experienced it locking up on the mobile net sometimes and this had solved the
> connectivity problem.
> I took the timer home as well...
> 
> What I *should* have done is powering the Ubuntu machine off the timer, because
> then I would be certain that if a lockup happened it would be solved within 24
> hours...

Power cycling a Ubuntu machine can be pretty rough on the file systems.

You need to find out what is happening with sshd.

Is there a firewall?  Is fail2ban running?

If a firewall is running, check its configuration.  If fail2ban is running, 
check its configuration.

Telneting to the machine on port 22, should *immediately* return a banner like 
this:

sauron% telnet localhost 22
Trying ::1...
Connected to localhost.
Escape character is '^]'.
SSH-2.0-OpenSSH_7.6p1 Ubuntu-4ubuntu0.5
^]
telnet> quit
Connection closed.

The fact that instead aspomint connects and then immediately closes the 
connection suggests that *something* is listening, but not a working instance 
of sshd. If nothing was listening (eg sshd had simply crashed), then you would 
have got:

sauron% telnet phone 22
Trying 192.168.250.40...
telnet: Unable to connect to remote host: Connection refused

("phone" is a cell phone, not running sshd)

> 
> 

-- 
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