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I want to use multiple private keys to connect to different servers or different portions of the same server (my uses are system administration of server, administration of Git, and normal Git usage within the same server). I tried simply stacking the keys in the id_rsa files to no avail.

Apparently a straightforward way to do this is to use the command

ssh -i <key location> login@server.example.com 

That is quite cumbersome.

Any suggestions as to how to go about doing this a bit easier?

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From my .ssh/config:

Host myshortname realname.example.com
    HostName realname.example.com
    IdentityFile ~/.ssh/realname_rsa # private key for realname
    User remoteusername

Host myother realname2.example.org
    HostName realname2.example.org
    IdentityFile ~/.ssh/realname2_rsa  # different private key for realname2
    User remoteusername

Then you can use the following to connect:

ssh myshortname

ssh myother

And so on.

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You can instruct ssh to try multiple keys in succession when connecting. Here's how:

$ cat ~/.ssh/config
IdentityFile ~/.ssh/id_rsa
IdentityFile ~/.ssh/id_rsa_old
IdentityFile ~/.ssh/id_ed25519
# ... and so on

$ ssh server.example.com -v
....
debug1: Next authentication method: publickey
debug1: Trying private key: /home/example/.ssh/id_rsa
debug1: read PEM private key done: type RSA
debug1: Authentications that can continue: publickey
debug1: Trying private key: /home/example/.ssh/id_rsa_old
debug1: read PEM private key done: type RSA
....
[server ~]$

This way you don't have to specify what key works with which server. It'll just use the first working key.

Also you would only enter a passphrase if a given server is willing to accept the key. As seen above ssh didn't try to ask for a password for .ssh/id_rsa even if it had one.

Surely it doesn't outbeat a per-server configuration as in other answers, but at least you won't have to add a configuration for all and every server you connect to!

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The answer from Randal Schwartz almost helped me all the way. I have a different username on the server, so I had to add the User keyword to my file:

Host           friendly-name
HostName       long.and.cumbersome.server.name
IdentityFile   ~/.ssh/private_ssh_file
User           username-on-remote-machine

Now you can connect using the friendly-name:

ssh friendly-name

More keywords can be found on the OpenSSH man page. NOTE: Some of the keywords listed might already be present in your /etc/ssh/ssh_config file.

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The previous answers have properly explained the way to create a configuration file to manage multiple ssh keys. I think, the important thing that also needs to be explained is the replacement of a host name with an alias name while cloning the repository.

Suppose, your company's GitHub account's username is abc1234. And suppose your personal GitHub account's username is jack1234

And, suppose you have created two RSA keys, namely id_rsa_company and id_rsa_personal. So, your configuration file will look like below:

# Company account
Host company
HostName github.com
PreferredAuthentications publickey
IdentityFile ~/.ssh/id_rsa_company

# Personal account
Host personal
HostName github.com
PreferredAuthentications publickey
IdentityFile ~/.ssh/id_rsa_personal

Now, when you are cloning the repository (named demo) from the company's GitHub account, the repository URL will be something like:

Repo URL: git@github.com:abc1234/demo.git

Now, while doing git clone, you should modify the above repository URL as:

git@company:abc1234/demo.git

Notice how github.com is now replaced with the alias "company" as we have defined in the configuration file.

Similary, you have to modify the clone URL of the repository in the personal account depending upon the alias provided in the configuration file.

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ssh-add ~/.ssh/xxx_id_rsa

Make sure you test it before adding with:

ssh -i ~/.ssh/xxx_id_rsa username@example.com

If you have any problems with errors sometimes changing the security of the file helps:

chmod 0600 ~/.ssh/xxx_id_rsa

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1. Generate an SSH key:

    $ ssh-keygen -t rsa -C <email1@example.com>
   

2. Generate another SSH key:

    $ ssh-keygen -t rsa -f ~/.ssh/accountB -C <email2@example.com>
   

   Now, two public keys (id_rsa.pub, accountB.pub) should be exists in the ~/.ssh/ directory.

    $ ls -l ~/.ssh     # see the files of '~/.ssh/' directory
   

3. Create configuration file ~/.ssh/config with the following contents:

    $ nano ~/.ssh/config
   
    Host bitbucket.org
        User git
        Hostname bitbucket.org
        PreferredAuthentications publickey
        IdentityFile ~/.ssh/id_rsa
   
    Host bitbucket-accountB
        User git
        Hostname bitbucket.org
        PreferredAuthentications publickey
        IdentitiesOnly yes
        IdentityFile ~/.ssh/accountB
   

4. Clone from default account.

    $ git clone git@bitbucket.org:username/project.git
   

5. Clone from the accountB account.

    $ git clone git@bitbucket-accountB:username/project.git
   

Note: Because of the User git directive, you can omit the git@ portion of the repo URL, shortening your clone command like so:

    $ git clone bitbucket-accountB:username/project.git

This is the only purpose of that directive. If you don't need it (e.g. you always copy-paste the git clone command from the website), you can leave it out of the config.

See More Here

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I would agree with Tuomas about using ssh-agent. I also wanted to add a second private key for work and this tutorial worked like a charm for me.

Steps are as below:

1. $ ssh-agent bash
2. $ ssh-add /path.to/private/key e.g ssh-add ~/.ssh/id_rsa
3. Verify by $ ssh-add -l
4. Test it with $ssh -v <host url> e.g ssh -v git@assembla.com

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Now, with the recent version of Git, we can specify sshCommand in the repository-specific Git configuration file:

  [core]
      repositoryformatversion = 0
      filemode = true
      bare = false
      logallrefupdates = true
      sshCommand = ssh -i ~/.ssh/id_rsa_user
   [remote "origin"]
      url = git@bitbucket.org:user/repo.git
      fetch = +refs/heads/*:refs/remotes/origin/*

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I had run into this issue a while back, when I had two Bitbucket accounts and wanted to had to store separate SSH keys for both. This is what worked for me.

I created two separate ssh configurations as follows.

Host personal.bitbucket.org
    HostName bitbucket.org
    User git
    IdentityFile /Users/username/.ssh/personal
Host work.bitbucket.org
    HostName bitbucket.org
    User git
    IdentityFile /Users/username/.ssh/work

Now when I had to clone a repository from my work account - the command was as follows.

git clone git@bitbucket.org:teamname/project.git

I had to modify this command to:

git clone git@**work**.bitbucket.org:teamname/project.git

Similarly the clone command from my personal account had to be modified to

git clone git@personal.bitbucket.org:name/personalproject.git

Refer this link for more information.

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For me on MacOs, the only working solution was to simply add this in file ~/.ssh/config:

Host *
  IdentityFile ~/.ssh/your_ssh_key
  IdentityFile ~/.ssh/your_ssh_key2
  IdentityFile ~/.ssh/your_ssh_key3
  AddKeysToAgent yes

your_ssh_key is without any extension. Don't use .pub.

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Use ssh-agent for your keys.

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Here is the solution that I used inspired from the answer of sajib-khan. The default configuration is not set; it's my personal account on GitLab and the other specified is my company account. Here is what I did:

Generate the SSH key

ssh-keygen -t rsa -f ~/.ssh/company -C "name.surname@company.com"

Edit the SSH configuration

nano ~/.ssh/config

    Host company.gitlab.com
    HostName gitlab.com
    PreferredAuthentications publickey
    IdentityFile ~/.ssh/company

Delete the cached SSH key(s)

ssh-add -D

Test it!

ssh -T git@company.gitlab.com

Welcome to GitLab, @hugo.sohm!

ssh -T git@gitlab.com

Welcome to GitLab, @HugoSohm!

Use it!

Company account

git clone git@company.gitlab.com:group/project.git

Personal/default account

git clone git@gitlab.com:username/project.git

Here is the source that I used.

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For those who are working with aws I would highly recommend working with EC2 Instance Connect.

Amazon EC2 Instance Connect provides a simple and secure way to connect to your instances using Secure Shell (SSH).

With EC2 Instance Connect, you use AWS Identity and Access Management (IAM) policies and principles to control SSH access to your instances, removing the need to share and manage SSH keys.

After installing the relevant packages (pip install ec2instanceconnectcli or cloning the repo directly) you can connect very easy to multiple EC2 instances by just changing the instance id:

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What is happening behind the scenes?

When you connect to an instance using EC2 Instance Connect, the Instance Connect API pushes a one-time-use SSH public key to the instance metadata where it remains for 60 seconds. An IAM policy attached to your IAM user authorizes your IAM user to push the public key to the instance metadata.

The SSH daemon uses AuthorizedKeysCommand and AuthorizedKeysCommandUser, which are configured when Instance Connect is installed, to look up the public key from the instance metadata for authentication, and connects you to the instance.

(*) Amazon Linux 2 2.0.20190618 or later and Ubuntu 20.04 or later comes preconfigured with EC2 Instance Connect. For other supported Linux distributions, you must set up Instance Connect for every instance that will support using Instance Connect. This is a one-time requirement for each instance.

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Links:

Set up EC2 Instance Connect
Connect using EC2 Instance Connect
Securing your bastion hosts with Amazon EC2 Instance Connect

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You can create a configuration file named config in your ~/.ssh folder. It can contain:

Host aws
    HostName *yourip*
    User *youruser*
    IdentityFile *idFile*

This will allow you to connect to machines like this

 ssh aws

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As mentioned on a Atlassian blog page, generate a config file within the .ssh folder, including the following text:

#user1 account
 Host bitbucket.org-user1
     HostName bitbucket.org
     User git
     IdentityFile ~/.ssh/user1
     IdentitiesOnly yes

 #user2 account
 Host bitbucket.org-user2
     HostName bitbucket.org
     User git
     IdentityFile ~/.ssh/user2
     IdentitiesOnly yes

Then you can simply checkout with the suffix domain and within the projects you can configure the author names, etc. locally.

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Multiple key pairs on GitHub

1.0 SSH configuration file

1.1 Create ~/.ssh/config

1.2 chmod 600 ~/.ssh/config (must)

1.3 Input the following into the file:

Host pizza

HostName github.com

PreferredAuthentications publickey # optional

IdentityFile ~/.ssh/privatekey1

Case A: Fresh new Git clone

Use this command to Git clone:

$ git clone git@pizza:yourgitusername/pizzahut_repo.git

Note: If you want to change the host name “pizza” of .ssh/config in the future, go into the Git cloned folder, edit .git/config file URL line (see case B)

Case B: Already have Git clone folder

2.1 Go to the cloned folder, and then go into the .git folder

2.2 Edit configuration file

2.3 Update the URL from *old to new:

(Old) URL = git@github.com:yourgitusername/pizzahut_repo.git

(New) URL = git@pizza:yourgitusername/pizzahut_repo.git

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IMPORTANT: You must start ssh-agent

You must start ssh-agent (if it is not running already) before using ssh-add as follows:

eval `ssh-agent -s` # start the agent

ssh-add id_rsa_2 # Where id_rsa_2 is your new private key file

Note that the eval command starts the agent on Git Bash on Windows. Other environments may use a variant to start the SSH agent.

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On Ubuntu 18.04 (Bionic Beaver) there is nothing to do.

After having created an second SSH key successfully the system will try to find a matching SSH key for each connection.

Just to be clear you can create a new key with these commands:

# Generate key make sure you give it a new name (id_rsa_server2)
ssh-keygen

# Make sure ssh agent is running
eval `ssh-agent`

# Add the new key
ssh-add ~/.ssh/id_rsa_server2

# Get the public key to add it to a remote system for authentication
cat ~/.ssh/id_rsa_server2.pub

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I love the approach to set the following in file ~/.ssh/config:

# Configuration for GitHub to support multiple GitHub  keys
Host  github.com
  HostName github.com
  User git

# UseKeychain adds each keys passphrase to the keychain so you
# don't have to enter the passphrase each time.
  UseKeychain yes

# AddKeysToAgent would add the key to the agent whenever it is
# used, which might lead to debugging confusion since then
# sometimes the one repository works and sometimes the
# other depending on which key is used first.
#  AddKeysToAgent yes

# I only use my private id file so all private
# repositories don't need the environment variable
# `GIT_SSH_COMMAND="ssh -i ~/.ssh/id_rsa"` to be set.
  IdentityFile ~/.ssh/id_rsa

Then in your repository you can create a .env file which contains the ssh command to be used:

GIT_SSH_COMMAND="ssh -i ~/.ssh/your_ssh_key"

If you then use e.g. dotenv the environment environment variable is exported automatically and whoop whoop, you can specify the key you want per project/directory. The passphrase is asked for only once since it is added to the keychain.

This solution works perfectly with Git and is designed to work on a Mac (due to UseKeychain).

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On CentOS 6.5 running OpenSSH_5.3p1 and OpenSSL 1.0.1e-fips, I solved the problem by renaming my key files so that none of them had the default name.

My .ssh directory contains id_rsa_foo and id_rsa_bar, but no id_rsa, etc.

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You can try this sshmulti npm package for maintaining multiple SSH keys.