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Problem is exactly as reported in

But it is not the "ssh_exchange_identification:" error, i.e., it's different than the ssh server: reasons for sudden "Connection closed by remote host" one.

I'm getting it while doing ssh -T:

$ ssh -T [email protected] Connection to github.com closed by remote host.

The following message is generated when using ssh -vvv

debug2: channel 0: request shell confirm 1 debug3: send packet: type 98 debug2: channel_input_open_confirmation: channel 0: callback done debug2: channel 0: open confirm rwindow 32000 rmax 35000 debug3: send packet: type 1 debug1: channel 0: free: client-session, nchannels 1 debug3: channel 0: status: The following connections are open: #0 client-session (t4 r43 i0/0 o0/0 fd 5/6 cc -1) Connection to github.com closed by remote host.

I've put the the full log (and diff with normal) to: https://www.diffchecker.com/LF2ZEb8j

For ssh -vvT [email protected], I've put the the log diff to:
https://www.diffchecker.com/WjmA7P0c
from which there isn't much revealing.

Once again, the above problem is from (connecting from) my remote server, of version 1:7.6p1-4ubuntu0.7, which has been working for years, but have now broken for a few weeks. Testing/connecting from my home machine (ver: 1:8.4p1-5) always OK.

Comments?
Is it that my openssh-client 1:7.6p1-4ubuntu0.7 is too old for github.com?

$ apt-cache policy openssh-client openssh-client: Installed: 1:7.6p1-4ubuntu0.7 Candidate: 1:7.6p1-4ubuntu0.7 Version table: *** 1:7.6p1-4ubuntu0.7 500 500 http://azure.archive.ubuntu.com/ubuntu bionic-updates/main amd64 Packages 100 /var/lib/dpkg/status 1:7.6p1-4ubuntu0.5 500 500 http://security.ubuntu.com/ubuntu bionic-security/main amd64 Packages 1:7.6p1-4 500 500 http://azure.archive.ubuntu.com/ubuntu bionic/main amd64 Packages
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3
  • Probably. Try upgrading ssh. If you can't find a PPA with an updated ssh client for Ubuntu "Bionic Beaver" 18.04, download the packaged source (not the upstream source but the source package for ubuntu's ssh package) from "Jammy Jellyfish" 22.04 or "Kinetic Kudu" 22.10 and rebuild it on your bionic system (check the dependencies carefully, this may also require upgrading libssl and//or other packages). Alternatively, upgrade the entire system to the latest ubuntu LTS ("Jammy Jellyfish", 22.04) - bionic is from 2018, two LTS releases behind the current LTS release. Commented Sep 17, 2022 at 5:54
  • GitHub doesn't have a problem with old SSH versions. I can connect to GitHub just fine with openssh-client 1:7.6p1-4ubuntu0.5 on Ubuntu 18.04 or even with openssh-client 1:1.9.1-1ubuntu0.10 0 on Ubuntu 14.04. It's possible that your machine is behind a firewall that blocks certain connections, and either changing the SSH version or changing certain options might make that firewall happy. Commented Sep 17, 2022 at 8:20
  • No @Gilles'SO-stopbeingevil', not a firewall issue -- my remote server is a normal Azure VM that I created myself, and it has been working for years, until recently. Besides, take a look of my answer -- same everything except openssh-client version will work. IMHO, it rules out anything except openssh-client version. Commented Sep 18, 2022 at 3:02

2 Answers 2

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3

This worked for me

Enabling SSH connections over HTTPS

If you are able to SSH into [email protected] over port 443, you can override your SSH settings to force any connection to GitHub.com to run through that server and port.

To set this in your SSH configuration file, edit the file at ~/.ssh/config, and add this section:

Host github.com Hostname ssh.github.com Port 443 User git

You can test that this works by connecting once more to GitHub.com:

$ ssh -T [email protected] > Hi USERNAME! You've successfully authenticated, but GitHub does not > provide shell access.

Using SSH over the HTTPS port

git clone ssh://[email protected]:443/USER_NAME/REPO_NAME.git
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Is it that my openssh-client 1:7.6p1-4ubuntu0.7 is too old for github.com?

I had an idea to verify right after I posted my question, and It turns out that the answer is YES!

Here is how I tested/proved it

  • Install debian:latest docker image
  • Do ssh -T [email protected] within the debian:latest docker image

So all else are the same except for the openssh-client version, and it works within the debian:latest docker container.

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