ssh-add returns with: "Error connecting to agent: No such file or directory"

Question

ssh-add alone is not working:

Error connecting to agent: No such file or directory

How should I use that tool?

Answer 1

The client tool ssh-add wants to communicate with the background process ssh-agent. You need to start the ssh-agent process first. On Linux, an Shell uses the environment variables SSH_AUTH_SOCK and SSH_AGENT_PID to identify the correct process to talk to.

You can start ssh-agent in multiple ways. Either by starting a new shell

ssh-agent bash

or by evaluating the script returned by ssh-agent in your current shell.

eval "$(ssh-agent)"

I suggest using the second method, because you keep all your history and variables.

Answer 2

In Windows PowerShell (run as admin):

1. Check the current status of ssh-agent:

   Get-Service | ?{$_.Name -like '*ssh-agent*'} | select -Property Name, StartType, Status

2. Enable the Service if it is disabled:

   Set-Service -Name ssh-agent -StartupType Manual

3. Start the Service:

   Start-Service ssh-agent

4. Add your key as before:

   ssh-add <path to the key>

Answer 3

The SSH agent is not running, or the environment variables that it sets are not available in the current environment (most importantly SSH_AUTH_SOCK), or they are set incorrectly (pointing to a dead agent).

You could start the agent in the current shell session using

eval "$(ssh-agent)"

or start a new shell session through the agent using

ssh-agent fish

(replace fish with whatever shell you are using). But since you say that you used to be able to use ssh-add without this, it leads me to believe that you've accidentally killed the agent (or it has terminated due to some other reason). The error message makes me think that the SSH_AUTH_SOCK environment variable is actually set, but that ssh-add can't find a valid communication socket at that path.

It would not surprise me if your usual way of doing things would work again if you completely logged out and logged in again, or rebooted the machine.

Answer 4

MacOS

Big Sur

In my edge case, the problem was I had somehow turned off the service, or it was trying to use bash instead of zsh. Not really sure, but this did the trick:

ssh-agent zsh

Answer 5

What I just stumbled uppon is that I couldn't add the key no matter what I tried. Reinstall openssh, start it in systemd, stop, restart, start ssh-agent, kill all ssh-agent processess running and try with a fresh one... I would always end up with that file or directory not found. In the end I removed all SSH keys that I had in my ~/.ssh, created a fresh one that I custom named, and it still didn't work. What did work is when I renamed that key to id_rsa. For some reason the agent picked that up automatically without the need to add the key to it and started working. Happened on Arch.