El Capitan seemed faster and more reliable on my laptop, so i took the plunge and upgraded my server. As expected, everything was a tad more responsive, and I was happy – until i tried to update git from my windows machine. Every push, pull and hair pull ended with the same : Server unexpectedly closed connection error.
Thankfully google eventually led me to https://blog.nytsoi.net/2015/07/13/putty-kex-error . It seems SourceTree (my git client), uses putty to access SSH based git systems – which mine is. And the putty in the current version of SourceTree, has a bug in the DH group key exchange that makes it not play well with a patched OpenSSL now in El Capitan.
Fortunately, as you can see from the website above, the patch is fast and painless – and sourcetree and I are happy once again.
“The fix was the following: In PuTTY, go to “Connection → SSH → Kex”. There, select “Diffie-Hellman group exchange” and move it to the bottom of the list, so it is not used. The connection should start working as normal again.”