Docs feedback: Test of ssh key configuration
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### Problem to solve
On the documentation page https://docs.gitlab.com/ee/ssh/ , paragraph "Testing that everything is set up correctly", the suggested command "ssh -T git@gitlab.cern.ch" did not work for me. Even in the verbose mode, it stopped at "debug1: Connecting to gitlab.cern.ch [188.185.68.13] port 22". However, I could clone without problem a repository from git@gitlab.cern.ch.
I had to do "ssh -v -v git@gitlab.cern.ch -p 7999" to make it work.
I was troubled by this, and I think the documentation should be adapted.
I work on a Dell Precision, Ubuntu 18.04, if that makes any difference.
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