How to fix Agent admitted failure to sign using the key in SSH

SSHINTERMEDIATEHIGHUpdated Jan 4, 2026· 183 views

SSH authentication fails when the SSH agent cannot sign your key. This typically occurs when your SSH key isn't loaded in the agent or the agent has configuration issues, preventing authentication to GitHub or other SSH servers.

Quick fix

Fixes Agent admitted failure to sign using the key

eval "$(ssh-agent -s)"
ssh-add
  1. Check if ssh-agent is running and load your key
  2. Add your SSH key if it has a non-standard path or filename
  3. Diagnose GNOME Keyring issues (Ubuntu)
  4. Bypass the agent temporarily to test
ssh — error
eval "$(ssh-agent -s)"
ssh-add
Agent admitted failure to sign using the key

What this error means

This error means your SSH agent was unable to use your private key to authenticate your identity. When you attempt an SSH connection, the server asks your client to prove it owns a specific key. The SSH agent is responsible for this signing process, but something is preventing it from working—either the key isn't loaded, the agent is misconfigured, or there's a compatibility issue with your key type or agent implementation.

Typical symptoms

  • SSH connections fail with 'Permission denied (publickey)' after the agent failure message
  • Git push/pull operations fail when using SSH URLs
  • SSH works with some key types but not others (e.g., ed25519 fails but RSA works)
  • Verbose SSH output shows 'No more authentication methods to try' after the agent failure
  • SSH works fine after rebooting or logging back in

Common causes

  1. Your SSH key is not loaded in the SSH agent—the most common cause
  2. GNOME Keyring (on Ubuntu) is intercepting SSH key requests and failing to handle your key format
  3. Incompatibility between your key type (ed25519, ECDSA, etc.) and the SSH agent implementation
  4. The SSH agent process crashed or became unresponsive
  5. SSH agent environment variable SSH_AUTH_SOCK is pointing to a broken socket

How to fix "Agent admitted failure to sign using the key"

1Check if ssh-agent is running and load your key

First, verify your SSH agent is running and load your key:

bash
eval "$(ssh-agent -s)"
ssh-add

This starts the SSH agent in the background and adds your default SSH key (~/.ssh/id_rsa). Test your connection:

bash
ssh -vT git@github.com

If you see "Hi username! You've successfully authenticated," the issue is resolved.

2Add your SSH key if it has a non-standard path or filename

If your key isn't in the default location, explicitly add it:

bash
eval "$(ssh-agent -s)"
ssh-add ~/.ssh/my_custom_key

Replace my_custom_key with your actual key filename. You can add multiple keys:

bash
ssh-add ~/.ssh/id_rsa
ssh-add ~/.ssh/id_ed25519
ssh-add ~/.ssh/github_personal_key

Verify all loaded keys with:

bash
ssh-add -l
3Diagnose GNOME Keyring issues (Ubuntu)

On Ubuntu, GNOME Keyring sometimes intercepts SSH requests but fails to handle certain key formats. Test if it's the problem:

bash
SSH_AUTH_SOCK=0 ssh -vT git@github.com

If this works, GNOME Keyring is likely the culprit. To permanently fix this on Ubuntu:

1. Reboot your system
2. Open Unity's Dash (or Activities menu)
3. Search for and open "Startup Applications"
4. Uncheck "SSH Key Agent"
5. Reboot again

After reboot, run eval "$(ssh-agent -s)" and ssh-add to use the standard SSH agent instead.

4Bypass the agent temporarily to test

To quickly test if the agent is the problem without making changes:

bash
ssh -o IdentityAgent=none -vT git@github.com

This bypasses the SSH agent entirely. If this works, the issue is definitely with your agent configuration. You can make this permanent by adding it to ~/.ssh/config:

bash
Host github.com
  IdentityAgent none

However, this is a workaround—investigate and fix the actual agent issue for better security and flexibility.

5Add SSH agent startup to your shell profile

To ensure the SSH agent runs every time you open a terminal, add this to your ~/.bashrc or ~/.zshrc:

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

This checks if an agent is already running before starting a new one, preventing multiple agent processes. Reload your shell:

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

Now your SSH keys will be automatically loaded when you open a new terminal.

Advanced notes

On macOS, the ssh-agent is managed by Keychain and typically works correctly. If you see this error on macOS, check if you're using a third-party SSH agent that's incompatible. On Linux, some desktop environments (GNOME, KDE) try to manage SSH keys automatically, but may have bugs or compatibility issues—using the standard SSH agent often resolves problems.

For ed25519 keys, there are rare edge cases where certain SSH agent implementations don't fully support this key type. If ed25519 keys fail but RSA keys work, try using RSA instead or updating your SSH client and agent to the latest versions.

If you're connecting through a firewall, VPN, or bastion host, the problem may not be the agent—test direct SSH connectivity first.

Frequently asked questions

What does "Agent admitted failure to sign using the key" mean?
This error means your SSH agent was unable to use your private key to authenticate your identity. When you attempt an SSH connection, the server asks your client to prove it owns a specific key. The SSH agent is responsible for this signing process, but something is preventing it from working—either the key isn't loaded, the agent is misconfigured, or there's a compatibility issue with your key type or agent implementation.
How do I fix "Agent admitted failure to sign using the key"?
SSH authentication fails when the SSH agent cannot sign your key. This typically occurs when your SSH key isn't loaded in the agent or the agent has configuration issues, preventing authentication to GitHub or other SSH servers.
What causes "Agent admitted failure to sign using the key"?
Your SSH key is not loaded in the SSH agent—the most common cause GNOME Keyring (on Ubuntu) is intercepting SSH key requests and failing to handle your key format Incompatibility between your key type (ed25519, ECDSA, etc.) and the SSH agent implementation
Is the "Agent admitted failure to sign using the key" error serious?
Yes. This is a high-severity error that usually blocks work until it is fixed, but the steps above resolve it.

Official resources & further reading