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I successfully used

ssh -q -i pubkey root@ 'halt'

for years now to halt a FreeBSD system (FreeNAS) from a linux box.

Suddenly, from out of nothing this stopped working: ssh hangs forever with this command. Since this is used in a backup script this is a desaster.

What could have happened that this suddenly happens? Is the problem more likely on the server side (FreeBSD) or client (Linux). How can I fix it (on the client side)?

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What has changes on the server / client side when it stopped working? – mpy Jul 2 '14 at 16:25
Nothing that I know ;-) Otherwise I would have reverted it and tried ... – divB Jul 2 '14 at 17:40
Try running ssh without the -q flag. – Roland Smith Jul 6 '14 at 13:00
up vote 0 down vote accepted

Check your SSH client config. TCPKeepAlive should not be set to no for the client.

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Have you tried to ssh in manually?

ssh -i pubkey root@

My only guess is for whatever reason the client's known_hosts got changed, deleted, etc. Or the entry in it doesn't match anymore which is possible. If openssl got changed (upgraded?) on the server side, then the known_hosts entry won't match.

And so when you ssh, even with a pubkey, you will get this if the known_hosts doesn't exist:

The authenticity of host ' (' can't be established. RSA key fingerprint is fa:7c:54:45:70:c2:70:f9:f2:3c:c9:75:4d:83:10:5b. Are you sure you want to continue connecting (yes/no)?

And so it is waiting for you to accept

Or you will get this if it doesn't match

test:~/.ssh # ssh @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @ @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY! Someone could be eavesdropping on you right now (man-in-the-middle attack)! It is also possible that the RSA host key has just been changed. The fingerprint for the RSA key sent by the remote host is fa:7c:54:45:70:c2:70:f9:f2:3c:c9:75:4d:83:10:5b. Please contact your system administrator. Add correct host key in /root/.ssh/known_hosts to get rid of this message. Offending key in /root/.ssh/known_hosts:1 RSA host key for has changed and you have requested strict checking. Host key verification failed. test:~/.ssh #

So try it manually. If it doesn't exist, you will need to accept it and then the known_hosts entry will be created and then the next time you ssh it should be fine

If it doesn't match, then edit your ~/.ssh/known_hosts and delete the entry for that host. Then when you ssh in again manually, accept it and recreate the known_hosts entry.

Only thing I can think of off the top of my head. Hope that's it!

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Unfortunately not. It also happens when I do it manually. I even can't kill the SSH session then with CTRL+C. I can only use CTRL+K in my screen session to kill the complete window. And login etc. is definitely successful. I can successfully issue the 'halt' command. So it seems the machine is indeed halted (I can't really verify because it's a remote box) but there is no timeout for SSH or so... – divB Jul 2 '14 at 21:50
So the machine is halting but you want your ssh session to exit? That's interesting. I would think that all along it might do this. Are you okay with running halt in the background? Maybe I misunderstand the issue. So the command you run is 'halt &' ? – ben Jul 2 '14 at 22:23
I just want to halt the system via SSH, yes. (and it always worked so far). Sure, running in background would be find but '&' doesn't help I think because it receives a HUP anyway. – divB Jul 3 '14 at 1:13

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