ssh-agent – SSH Key Manager

The ssh-agent command is a program that helps you manage your SSH keys. SSH keys are used to authenticate secure connections between two computers, and they are often used by system administrators and developers to log in to remote servers. The ssh-agent command is used to manage your SSH keys, allowing you to add, remove, and list keys, as well as providing a secure way to store and use your keys.

Overview

The ssh-agent command is used to start a new instance of the SSH agent. Once started, the agent can be used to add SSH keys to the agent’s cache so that they can be used for authentication without having to enter the key’s passphrase each time. The agent can also be used to remove keys from the cache, list the keys that are currently in the cache, and to kill the agent.

To start the agent, simply run the ssh-agent command:

ssh-agent

This will start the agent and output some environment variables that need to be set:

SSH_AUTH_SOCK=/tmp/ssh-XXXXXXXXXX/agent.XXXXXX; export SSH_AUTH_SOCK;
SSH_AGENT_PID=XXXXX; export SSH_AGENT_PID;
echo Agent pid XXXXX;

You need to copy and paste these environment variables into your shell to use the agent. You can do this by running the following command:

eval $(ssh-agent)

Now that the agent is running, you can add your SSH key to the agent’s cache by running the following command:

ssh-add /path/to/ssh/key

This will add the key to the agent’s cache and prompt you for the key’s passphrase. Once the key is added, you can use it to authenticate with remote servers without having to enter the passphrase each time.

To list the keys that are currently in the agent’s cache, run the following command:

ssh-add -l

This will list the fingerprints of the keys that are currently in the cache.

To remove a key from the agent’s cache, run the following command:

ssh-add -d /path/to/ssh/key

This will remove the key from the agent’s cache.

To kill the agent, run the following command:

ssh-agent -k

This will kill the agent and remove all keys from the cache.

Options

The following options are available for the ssh-agent command:

Option Description
-a Bind the agent to the specified socket.
-c Generate a PKCS #11 URI for the agent.
-D Debug mode.
-k Kill the agent.
-s Output Bourne shell commands to set the environment variables.

Troubleshooting Tips

If you are having trouble using the ssh-agent command, here are some tips that may help:

  • Make sure that the agent is running by running the eval $(ssh-agent) command.
  • Make sure that your SSH key is added to the agent’s cache by running the ssh-add command.
  • Make sure that the agent’s environment variables are set correctly in your shell.
  • If you are having trouble connecting to a remote server, make sure that your SSH key is authorized on the remote server.

Notes

  • The ssh-agent command is often used in conjunction with the ssh command to provide secure authentication for remote connections.
  • The agent’s cache is stored in memory, so keys will be lost if the agent is killed or if the computer is restarted.
  • The agent can be started automatically when you log in to your computer by adding the eval $(ssh-agent) command to your shell’s startup script.