Specify an SSH key for git push for a given domain

Question

I have the following use case: I would like to be able to push to [email protected]:gitolite-admin using the private key of user gitolite-admin, while I want to push to [email protected]:some_repo using 'my own' private key. AFAIK, I can't solve this using ~/.ssh/config, because the user name and server name are identical in both cases. As I mostly use my own private key, I have that defined in ~/.ssh/config for [email protected]. Does anyone know of a way to override the key that is used for a single git invocation?

(Aside: gitolite distinguishes who is doing the pushing based on the key, so it's not a problem, in terms of access, ownership and auditing, that the user@server string is identical for different users.)

Solution 1

Even if the user and host are the same, they can still be distinguished in ~/.ssh/config. For example, if your configuration looks like this:

Host gitolite-as-alice
  HostName git.company.com
  User git
  IdentityFile /home/whoever/.ssh/id_rsa.alice
  IdentitiesOnly yes

Host gitolite-as-bob
  HostName git.company.com
  User git
  IdentityFile /home/whoever/.ssh/id_dsa.bob
  IdentitiesOnly yes

Then you just use gitolite-as-alice and gitolite-as-bob instead of the hostname in your URL:

git remote add alice git@gitolite-as-alice:whatever.git
git remote add bob git@gitolite-as-bob:whatever.git

Note

You want to include the option IdentitiesOnly yes to prevent the use of default ids. Otherwise, if you also have id files matching the default names, they will get tried first because unlike other config options (which abide by "first in wins") the IdentityFile option appends to the list of identities to try. See: https://serverfault.com/questions/450796/how-could-i-stop-ssh-offering-a-wrong-key/450807#450807

Solution 2

You can utilize git environment variable GIT_SSH_COMMAND. Run this in your terminal under your git repository:

GIT_SSH_COMMAND='ssh -i ~/.ssh/your_private_key' git submodule update --init

Replace ~/.ssh/your_private_key with the path of ssh private key you wanna use. And you can change the subsequent git command (in the example is git submodule update --init) to others like git pull, git fetch, etc.

Solution 3

An alternative approach to the one offered above by Mark Longair is to use an alias that will run any git command, on any remote, with an alternative SSH key. The idea is basically to switch your SSH identity when running the git commands.

Advantages relative to the host alias approach in the other answer:

• Will work with any git commands or aliases, even if you can't specify the remote explicitly.
• Easier to work with many repositories because you only need to set it up once per client machine, not once per repository on each client machine.

I use a few small scripts and a git alias admin. That way I can do, for example:

git admin push 

To push to the default remote using the alternative ("admin") SSH key. Again, you could use any command (not just push) with this alias. You could even do git admin clone ... to clone a repository that you would only have access to using your "admin" key.

Step 1: Create the alternative SSH keys, optionally set a passphrase in case you're doing this on someone else's machine.

Step 2: Create a script called “ssh-as.sh” that runs stuff that uses SSH, but uses a given SSH key rather than the default:

#!/bin/bash
exec ssh ${SSH_KEYFILE+-i "$SSH_KEYFILE"} "$@"

Step 3: Create a script called “git-as.sh” that runs git commands using the given SSH key.

#!/bin/bash
SSH_KEYFILE=$1 GIT_SSH=${BASH_SOURCE%/*}/ssh-as.sh exec git "${@:2}"

Step 4: Add an alias (using something appropriate for “PATH_TO_SCRIPTS_DIR” below):

# Run git commands as the SSH identity provided by the keyfile ~/.ssh/admin
git config --global alias.admin \!"PATH_TO_SCRIPTS_DIR/git-as.sh ~/.ssh/admin"

More details at: http://noamlewis.wordpress.com/2013/01/24/git-admin-an-alias-for-running-git-commands-as-a-privileged-ssh-identity/

Solution 4

Configure your repository using git config

git config --add --local core.sshCommand 'ssh -i <<<PATH_TO_SSH_KEY>>>'

This applies to your local repository only.

Solution 5

I've cribbed together and tested with github the following approach, based on reading other answers, which combines a few techniques:

• correct SSH config
• git URL re-writing

The advantage of this approach is, once set up, it doesn't require any additional work to get it right - for example, you don't need to change remote URLs or remember to clone things differently - the URL rewriting makes it all work.

~/.ssh/config

# Personal GitHub
Host github.com
  HostName github.com
  User git
  AddKeysToAgent yes
  UseKeychain yes
  IdentityFile ~/.ssh/github_id_rsa

# Work GitHub
Host github-work
  HostName github.com
  User git
  AddKeysToAgent yes
  UseKeychain yes
  IdentityFile ~/.ssh/work_github_id_rsa

Host *
  IdentitiesOnly yes

~/.gitconfig

[user]
    name = My Name
    email = [email protected]

[includeIf "gitdir:~/dev/work/"]
    path = ~/dev/work/.gitconfig

[url "github-work:work-github-org/"]
    insteadOf = [email protected]:work-github-org/

~/dev/work/.gitconfig

[user]
    email = [email protected]

As long as you keep all your work repos under ~/dev/work and personal stuff elsewhere, git will use the correct SSH key when doing pulls/clones/pushes to the server, and it will also attach the correct email address to all of your commits.

References:

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