Secure Shell (SSH) is a secure protocol used in networking to connect to and communicate with remote servers. It uses a pair of cryptographic keys, namely a private key and a public key, which form the basis for the identity of a client or a server. However, you may sometimes encounter the following error while working with SSH: “Load key ‘~/.ssh/id_rsa.pub’: invalid format”. This typically signifies an issue with the format of the SSH key pair, specifically the public key.
This article aims to provide a comprehensive guide to troubleshooting this error, discussing its probable causes and proposing solutions to fix it.
Causes for the Error
- Incorrect Key Format: The main cause of this error is typically an issue with the public key’s format. An SSH key must follow a specific format to be recognized and used by the SSH protocol. If the format is not correct, an invalid format error is triggered.
- Mismatch of Key Pair: This error can also occur if there is a mismatch between the private key and the public key. The keys work in pairs, so if you generate a new key, you must replace both the private and public keys.
- Incorrect File Permissions: SSH requires specific file permissions for your keys to work correctly. If these permissions are not correct, this could lead to the invalid format error.
1. Verify Key Format
Check your SSH public key to ensure it’s correctly formatted. A properly formatted SSH key will start with “ssh-rsa”, “ssh-ed25519”, or similar depending on the algorithm used, followed by a space, then the key content (a long string of characters), and optionally ending with a comment.
If your key is not correctly formatted, the simplest solution is to generate a new one using the ssh-keygen command:
ssh-keygen -t rsa -b 4096 -C "[email protected]"
This command generates a new SSH key using RSA algorithm with a key size of 4096 bits.
2. Check Key Pair Consistency
Make sure that the public key (id_rsa.pub) and the private key (id_rsa) match. If you’ve regenerated your SSH keys and only replaced one, you may experience the invalid format error.
To solve this, ensure that you replace both keys whenever you generate a new key pair. Alternatively, you could generate a public key from the existing private key using the following command:
ssh-keygen -y -f ~/.ssh/id_rsa > ~/.ssh/id_rsa.pub
This command generates a new public key based on the existing private key.
3. Check File Permissions
SSH requires that your private keys are only accessible by you. If the permissions are set incorrectly, you may face the invalid format error. You can fix this by setting the correct permissions using the chmod command:
chmod 700 ~/.ssh
chmod 600 ~/.ssh/id_rsa
These commands set the ~/.ssh directory to be accessible only by your user and makes the private key readable and writable only by your user, which is the required permission setting for SSH keys.
Troubleshooting the “Load key ‘~/.ssh/id_rsa.pub’: Invalid Format” error involves checking the key format, ensuring that the key pair is consistent, and verifying the file permissions. By following the suggested steps, you should be able to resolve the issue and continue with your SSH operations. If the problem persists after following these steps, it may be an indication of a more complex issue, and reaching out to your network administrator or support community may be necessary.