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Linux is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is typically packaged in a Linux distribution (or distro for short).

Distributions include the Linux kernel and supporting system software and libraries, many of which are provided by the GNU Project. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses the name GNU/Linux to emphasize the importance of GNU software, causing some controversy.

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SSH login without user name? (docs.gitlab.com)

submitted 6 months ago by Aarkon@feddit.de to c/linux@lemmy.ml

23 comments fedilink hide all child comments

I was reading GitLab's documentation (see link) on how to write to a repository from within the CI pipeline and noticed something: The described Docker executor is able to authenticate e.g. against the Git repository with only a private SSH key, being told absolutely nothing about the user's name it is associated with.
If I'm correct, that would mean that technically, I could authenticate to an SSH server without supplying my name if I use a private key?

I know that when I don't supply a user explicitly like ssh user@server or via .ssh/config, the active environment's user is used automatically, that's not what I'm asking.

The public key contains a user name/email address string, I'm aware, is the same information also encoded into the private key as well? If yes, I don't see the need to hand that info to an SSH call. If no, how does the SSH server know which public key it's supposed to use to challenge my private key ownership? It would have to iterate over all saved keys, which sounds rather inefficient to me and potentially unsafe (timing attacks etc.).

I hope I'm somewhat clear, for some reason I find it really hard to phrase this question.

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[–] bizdelnick@lemmy.ml 18 points 6 months ago (8 children)

Technically, you always use a username, however in case of Gitlab that SSH username is always git. When an SSH client connects to server, it offers an authentication method. Gitlab accepts that method only if it is a publickey and the fingerprint of the offered key maps to the known Gitlab user.

[–] Michal@programming.dev 4 points 6 months ago (7 children)

It's a blessing and a curse. I have two gitlab accounts on the same server - private and work. I can't use the same key for both as the key is used to distinguish git users, and git doesn't make it easy to select which key you want to use to pull or clone particular repo.

[–] bizdelnick@lemmy.ml 8 points 6 months ago (1 children)

git config core.sshCommand 'ssh -i <path to desired key>'

[–] ReversalHatchery@beehaw.org 3 points 6 months ago (1 children)

Hmm, with a similar technique one could even create git command aliases for running git with specific ssh private keys

[–] vvv@programming.dev 5 points 6 months ago

Better than that, git config supports conditional includes, based on a repo URL or path on disk. So you can have a gitconfig per organization or whatever, which specifies an sshCommand and thus an ssh key.

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