SSH "connection closed" instantly

Question

SSH "connection closed" instantly

Alright, I have a feeling this is my own doing as a few months ago I was experimenting with public/private key authentication. Now I can't SSH into one of my work computers. That is, no machine can SSH into it and it can't SSH into itself.

When I run the command

ssh [myusername]@localhost

from the machine in question, I get:

Connection closed by ::1

Now, when I run

ssh -vv [myusername]@localhost

I get:

OpenSSH_5.2p1, OpenSSL 0.9.8l 5 Nov 2009
debug1: Reading configuration data /etc/ssh_config
debug2: ssh_connect: needpriv 0
debug1: Connecting to localhost [::1] port 22.
debug1: Connection established.
debug1: identity file /Users/pro01/.ssh/identity type -1
debug1: identity file /Users/pro01/.ssh/id_rsa type -1
debug1: identity file /Users/pro01/.ssh/id_dsa type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_5.2
debug1: match: OpenSSH_5.2 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.2
debug2: fd 3 setting O_NONBLOCK
debug1: SSH2_MSG_KEXINIT sent
Connection closed by ::1

I've tried searching around but haven't had any luck. Anyone have any ideas as to how I can fix this and get my SSH working again?

Mac OS X (10.6.7)

Posted on Apr 20, 2011 8:53 AM

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Answer 1

Jan 24, 2017 4:55 AM in response to JeffMurchison

Unfortunately, this did NOT work for me. I found that permissions of 600 on the ssh_host_rsa_key were adequate for OS X Yosemite 10.10.5, but that on some other machines (running Mac OS X El Capitan 10.11.6) this solution did not work.

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Answer 2

etresoft

Level 8

46,972 points

Apr 20, 2011 9:05 AM in response to JeffMurchison

What model/make/version are you connecting from and to?

Can you connect to a different account on that machine? If so, the problem may be in the one accout's .ssh directory. If ssh doesn't work for any account, then you need to restore working /etc/ssh_config and /etc/sshd_config files.

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Answer 3

Apr 20, 2011 9:11 AM in response to etresoft

Mac Pro / 10.6.6 (realized that I put 10.6.7 in my post, oops).

It's all accounts. What's the best way to restore them? I just tried using copies from another working machine but no dice.

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Answer 4

etresoft

Level 8

46,972 points

Apr 20, 2011 11:58 AM in response to JeffMurchison

You should be able to copy in versions from known good machines. You will have to restart sshd. While there are elegant ways to do this, an inelegant restart works well too.

If that doesn't do it, try running ssh -vv from two good machines and comparing the result with the same command on the broken one.

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Answer 5

Apr 20, 2011 12:09 PM in response to etresoft

Like I mentioned, I tried copying versions from another machine (working, obviously) and it does not work.

Comparing the two, things start to differentiate at:

debug1: SSH2_MSG_KEXINIT sent

On other working machines it will be followed by:

debug1: SSH2_MSG_KEXINIT received

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Answer 6

BobHarris

Level 9

53,417 points

Apr 20, 2011 12:41 PM in response to JeffMurchison

It would appear the server is killing your connection.

Is the Firewall enabled? try disabling it.

Look in /var/log/secure.log to see if sshd is issuing any useful information.

You can change the sshd debugging level into /var/log/secure.log using

/etc/sshd_config

adding

LogLevel DEBUG3

Then stop/start System Preferences -> Sharing -> Remote Login

What might be helpful in analyzing the DEBUG3 output is to do the same thing to a working system, and then compare the /var/log/secure.log output and see where the login sessions differ.

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Answer 7

Jan 9, 2012 5:25 PM in response to JeffMurchison

Alright, so funny enough I stumbled upon this thread when I encountered the same issue on another computer. This thread was the top result on Google.

I did a bit of poking and prodding, looking at the console and logs and verbose output and I figured it out. I figured I would add the answer here in case anyone else has the same issue.

The problem was permissions on the file

/etc/ssh_host_dsa_key

were set to 777 when they should have been set to 700.

Running the following command fixed the issue:

sudo chmod 700 /etc/ssh_host_dsa_key

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Answer 8

Jun 8, 2012 3:26 PM in response to JeffMurchison

Jeff's solution instantly fixed the problem I've been having ever since upgrading to OS X 10.7. THANK YOU!!

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Answer 9

Oct 4, 2012 10:21 AM in response to JeffMurchison

This also worked perfectly with an upgrade to 10.8 as well. Thanks

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Answer 10

Jan 30, 2015 10:41 PM in response to JeffMurchison

thank you Jeff! that worked!

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