The output from this command should indicate that AllowAgentForwarding is set. You can check that agent forwarding is permitted by SSHing into the server and running sshd_config. Your server must allow SSH agent forwarding on inbound connectionsĪgent forwarding may also be blocked on your server. Deleting this line from the file should get agent forwarding working once more. In this example, our /etc/ssh_config file specifically says ForwardAgent no, which is a way to block agent forwarding. We can inspect that file to see if it's overriding our options by running the following commands: $ cat /etc/ssh_config # Print out the /etc/ssh_config file > Host * > SendEnv LANG LC_* > ForwardAgent no In the example above, the file ~/.ssh/config is loaded first, then /etc/ssh_config is read. You can check if a system configuration file is being used by entering the following command in the terminal: $ ssh -v URL # Connect to the specified URL with verbose debug output > OpenSSH_8.1p1, LibreSSL 2.7.3 > debug1: Reading configuration data /Users/YOU/.ssh/config > debug1: Applying options for > debug1: Reading configuration data /etc/ssh_config > debug1: Applying options for * $ exit # Returns to your local command prompt Sometimes, system configurations disallow SSH agent forwarding. Your system must allow SSH agent forwarding Our guide on generating SSH keys can help you set up your SSH keys locally. Url = +refs/heads/*:refs/remotes/origin/*īefore you can make your keys work through agent forwarding, they must work locally first. git/config file on your server and ensure the URL is an SSH-style URL like below: SSH forwarding only works with SSH URLs, not HTTP(s) URLs. You must be using an SSH URL to check out code Here are some things to look out for when troubleshooting SSH agent forwarding. If the variable is not set, it means that agent forwarding is not working: $ echo " $SSH_AUTH_SOCK" # Print out the SSH_AUTH_SOCK variable > $ ssh -T # Try to SSH to github > Permission denied (publickey). If you're unsure if your local key is being used, you can also inspect the SSH_AUTH_SOCK variable on your server: $ echo " $SSH_AUTH_SOCK" # Print out the SSH_AUTH_SOCK variable > /tmp/ssh-4hNGMk8AZX/agent.79453 If all is well, you'll get back the same prompt as you did locally. To test that agent forwarding is working with your server, you can SSH into your server and run ssh -T once more. You should only add servers you trust and that you intend to use with agent forwarding. They won't have direct access to the keys, but they will be able to use them as you while the connection is established. That's not really a good idea, as you'd be sharing your local SSH keys with every server you SSH into. Warning: You may be tempted to use a wildcard like Host * to just apply this setting to all SSH connections. If this file doesn't exist, you can create it by entering touch ~/.ssh/config in the terminal.Įnter the following text into the file, replacing with your server's domain name or IP: Host Using your favorite text editor, open up the file at ~/.ssh/config. Let's set up SSH to allow agent forwarding to your server. You can test that your local key works by entering ssh -T in the terminal: $ ssh -T # Attempt to SSH in to github > Hi USERNAME! You 've successfully authenticated, but GitHub does not provide > shell access. You can use our guide on generating SSH keys if you've not done this yet. Setting up SSH agent forwardingĮnsure that your own SSH key is set up and working. This is sort of like asking a friend to enter their password so that you can use their computer.Ĭheck out Steve Friedl's Tech Tips guide for a more detailed explanation of SSH agent forwarding. The nifty thing is, you can choose to let servers access your local ssh-agent as if they were already running on the server. It's a program that runs in the background and keeps your key loaded into memory, so that you don't need to enter your passphrase every time you need to use the key. If you've already set up an SSH key to interact with GitHub, you're probably familiar with ssh-agent. It allows you to use your local SSH keys instead of leaving keys (without passphrases!) sitting on your server. SSH agent forwarding can be used to make deploying to a server simple.
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