How to fix ssh-add: Could not add identity: communication with agent failed in SSH

First, verify whether ssh-agent is actually running in your current session.

On Linux/macOS:

ps aux | grep ssh-agent

Look for a line that shows ssh-agent (not grep). If you don't see it, the agent is not running.

Alternatively, check the environment variables:

echo $SSH_AUTH_SOCK
echo $SSH_AGENT_PID

Both should be set. If they're empty, the agent is not initialized.

On Windows (PowerShell):

Get-Service ssh-agent | Select-Object Status

Should show Running. If it shows Stopped, proceed to Step 2.

If ssh-agent is not running, start it with:

eval "$(ssh-agent -s)"

This command:
- Starts ssh-agent in the background
- Sets SSH_AUTH_SOCK and SSH_AGENT_PID environment variables
- Makes them available to all subsequent commands in that shell

You should see output like:

Agent pid 1234

Now try ssh-add again:

ssh-add ~/.ssh/id_rsa

It should work. Verify with:

ssh-add -l

This lists all identities currently managed by the agent.

If you're on Windows and the ssh-agent service is stopped, start it.

As a one-time fix (for current session):

Start-Service ssh-agent

Then try ssh-add:

ssh-add C:\Users\YourUsername\.ssh\id_rsa

To make it automatic (recommended):

Set-Service -Name ssh-agent -StartupType Automatic
Start-Service ssh-agent

This sets ssh-agent to start automatically on every reboot, so you won't encounter this issue again.

To avoid this error in future terminal sessions, add the agent initialization to your shell startup file.

For Bash, add this to ~/.bashrc:

if [ -z "$SSH_AUTH_SOCK" ]; then
   eval "$(ssh-agent -s)"
fi

For Zsh, add this to ~/.zshrc:

if [ -z "$SSH_AUTH_SOCK" ]; then
   eval "$(ssh-agent -s)"
fi

Then reload your shell:

source ~/.bashrc    # or source ~/.zshrc

Now every time you open a new terminal, SSH agent will be automatically started if it's not already running.

If the agent is running but ssh-add still fails, check the socket file permissions.

ls -la $SSH_AUTH_SOCK

The socket should be owned by your user with restrictive permissions:

srwx------ 1 youruser staff 0 Jan  4 10:30 /tmp/ssh-XXXXXXXXXX/agent.12345

If permissions are wrong, fix them:

chmod 700 $(dirname $SSH_AUTH_SOCK)
chmod 600 $SSH_AUTH_SOCK

If the socket file doesn't exist, restart the agent:

eval "$(ssh-agent -s)"

On GNOME Desktop (Ubuntu, Fedora), the display manager may set SSH_AUTH_SOCK to GNOME Keyring instead of ssh-agent, causing conflicts.

Check which agent is active:

echo $SSH_AUTH_SOCK
file $SSH_AUTH_SOCK

If it shows a GNOME Keyring path instead of /tmp/ssh-*/agent.*, that's the problem.

Solution: Start SSH agent in your shell configuration AFTER login. Add to ~/.bashrc or ~/.zshrc:

if [ -S "$SSH_AUTH_SOCK" ]; then
  # Check if current SSH_AUTH_SOCK is GNOME Keyring
  if file "$SSH_AUTH_SOCK" | grep -q "socket"; then
    # It's a real socket, keep it
    true
  else
    # Start our own ssh-agent
    eval "$(ssh-agent -s)"
  fi
else
  eval "$(ssh-agent -s)"
fi

Then open a new shell (important: use a shell command, not a GUI shortcut) and test:

ssh-add ~/.ssh/id_rsa

Once SSH agent is running, add your private keys.

Basic usage:

ssh-add ~/.ssh/id_rsa

If your key has a passphrase, you'll be prompted to enter it once. The agent caches it in memory for the session.

Add all keys in ~/.ssh:

ssh-add ~/.ssh/id_*

Verify keys are loaded:

ssh-add -l

Should list your keys with their fingerprints.

Remove a key from agent (optional):

ssh-add -d ~/.ssh/id_rsa

Remove all keys from agent (optional):

ssh-add -D