[git] Specify an SSH key for git push for a given domain

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.)

One Unix based systems (Linux, BSD, Mac OS X), the default identity is stored in the directory $HOME/.ssh, in 2 files: private key: $HOME/.ssh/id_rsa public key: $HOME/.ssh/id_rsa.pub When you use ssh without option -i, it uses the default private key to authenticate with remote system.

If you have another private key you want to use, for example $HOME/.ssh/deploy_key, you have to use ssh -i ~/.ssh/deploy_key ...

It is annoying. You can add the following lines in to your $HOME/.bash_profile : ssh-add ~/.ssh/deploy_key ssh-add ~/.ssh/id_rsa

So each time you use ssh or git or scp (basically ssh too), you don't have to use option -i anymore.

You can add as many keys as you like in the file $HOME/.bash_profile.

I am using Git Bash on Win7. The following worked for me.

Create a config file at ~/.ssh/config or c:/users/[your_user_name]/.ssh/config. In the file enter:

Host your_host.com
     IdentityFile [absolute_path_to_your_.ssh]\id_rsa

I guess the host has to be a URL and not just a "name" or ref for your host. For example,

Host github.com
     IdentityFile c:/users/[user_name]/.ssh/id_rsa

The path can also be written in /c/users/[user_name]/.... format

The solution provided by Giordano Scalzo is great too. https://stackoverflow.com/a/9149518/1738546

Configure your repository using git config. For example:

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

You might need to remove (or comment out) default Host configuration

To use a specific key on the fly:

GIT_SSH_COMMAND='ssh -i $HOME/.ssh/id_ed25519 -o IdentitiesOnly=yes -F /dev/null' git push origin c13_training_network

Explanation:

• local ENV var before doing the push
• -i specifies key
• -F forces an empty config so your global one doesn't overwrite this temporary command

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/

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:

• 1

• 2

If using Git's version of ssh on windows, the identity file line in the ssh config looks like

IdentityFile /c/Users/Whoever/.ssh/id_rsa.alice

where /c is for c:

To check, in git's bash do

cd ~/.ssh
pwd 

you most specified in the file config key ssh:

# Default GitHub user
Host one
 HostName gitlab.com
 User git
 PreferredAuthentications publickey
 IdentityFile ~/.ssh/key-one
 IdentitiesOnly yes

#two user
Host two
 HostName gitlab.com
 User git
 PreferredAuthentications publickey
 IdentityFile ~/.ssh/key-two
 IdentitiesOnly yes

As someone else mentioned, core.sshCommand config can be used to override SSH key and other parameters.

Here is an exmaple where you have an alternate key named ~/.ssh/workrsa and want to use it for all repositories cloned under ~/work.

1. Create a new .gitconfig file under ~/work:

[core]
  sshCommand = "ssh -i ~/.ssh/workrsa"

2. In your global git config ~/.gitconfig, add:

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

Another alternative is to use ssh-ident, to manage your ssh identities.

It automatically loads and uses different keys based on your current working directory, ssh options, and so on... which means you can easily have a work/ directory and private/ directory that transparently end up using different keys and identities with ssh.

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.

One possibility to use ~/.ssh/config is to use the Match restriction instead of the Host restriction. In particular Match Exec calls a shell command to decide whether to apply the declarations or not. In bash you could use the following command:

[ [email protected]:gitolite-admin = $(git config --get remote.origin.url)'' ]

This uses the bash [ command to verify if two strings are equal. In this case it is testing if the string [email protected]:gitolite-admin matches the output that is obtained from the $(git config --get remote.origin.url)'' command.

You can use any other command that identifies the repository that the shell is on. For this to work it is important to have the $SHELL variable defined to your shell, in my case /bin/bash. The full example would then be the following ~/.ssh/config:

Match Exec "[ [email protected]:gitolite-admin = $(git config --get remote.origin.url)'' ]"
  IdentityFile ~/.ssh/gitolite-admin
  IdentitiesOnly yes
  ForwardAgent no
  ForwardX11 no
  ForwardX11Trusted no

Match Exec "[ [email protected]:some_repo = $(git config --get remote.origin.url)'' ]"
  IdentityFile ~/.ssh/yourOwnPrivateKey
  IdentitiesOnly yes
  ForwardAgent no
  ForwardX11 no
  ForwardX11Trusted no

In this example I assumed that ~/.ssh/yourOwnPrivateKey contains your own private key and that ~/.ssh/gitolite-admin contains the private key of the user gitolite-admin. I included the IdentitiesOnly yes declaration to make sure that only one key is offered to the git server, mentioned by Mark Longair. The other declarations are just standard ssh options for git.

You can add this configuration if you have several some_repo that you want to use with different keys. If you have several repositories at [email protected] and most of them use the ~/.ssh/yourOwnPrivateKey it makes more sense to include this key as default for the host. In this case the ~/.ssh/config would be:

Match Exec "[ [email protected]:gitolite-admin = $(git config --get remote.origin.url)'' ]"
  IdentityFile ~/.ssh/gitolite-admin
  IdentitiesOnly yes

Host git.company.com
  IdentityFile ~/.ssh/yourOwnPrivateKey
  IdentitiesOnly yes
  ForwardAgent no
  ForwardX11 no
  ForwardX11Trusted no

Note that the order matters and the Host git.company.com restriction should appear after the Match Exec one or ones.

From git 2.10 upwards it is also possible to use the gitconfig sshCommand setting. Docs state :

If this variable is set, git fetch and git push will use the specified command instead of ssh when they need to connect to a remote system. The command is in the same form as the GIT_SSH_COMMAND environment variable and is overridden when the environment variable is set.

An usage example would be: git config core.sshCommand "ssh -i ~/.ssh/[insert_your_keyname]

In some cases this doesn't work because ssh_config overriding the command, in this case try ssh -i ~/.ssh/[insert_your_keyname] -F /dev/null to not use the ssh_config.