The "Too many authentication failures for user" error is a relatively common issue that CentOS 7 users may encounter when attempting to log in via SSH (Secure Shell). This error indicates that the maximum allowed number of authentication attempts has been exceeded. The error is often caused by misconfiguration on either the client or server side, or potentially by a security breach. In the following steps, we'll describe how to effectively identify and resolve this problem.
Causes of the Error
- Too Many Keys Offered by the Client: The SSH client may offer all keys stored in the ssh agent during login attempts, which can exceed the maximum allowed authentication attempts on the server.
- Incorrect Server Configuration: The server may have a too low limit set for the maximum number of authentication attempts.
Resolving the Issue
1. Check and Adjust SSH Client Configuration
On the client side, you can specify which key you want to use for authentication, thereby reducing the number of authentication attempts. In the ~/.ssh/config file, add the following configuration for the specific host:
Host myserver.com
HostName myserver.com
IdentityFile ~/.ssh/my_key_rsa
IdentitiesOnly yes
This way, you ensure that the SSH client only offers the specified key, avoiding the error caused by too many authentication attempts.
2. Increase the Limit for Authentication Attempts on the Server Side
If you have access to the server, you can increase the limit for the maximum number of unsuccessful authentication attempts. Modify the SSH daemon configuration file /etc/ssh/sshd_config and increase the value of MaxAuthTries. For example:
MaxAuthTries 6
After modifying the configuration, don't forget to restart the SSH daemon service:
sudo systemctl restart sshd
3. Security Check
It's also essential to verify whether these unsuccessful attempts are not due to unauthorized access attempts. To check, review the SSH login logs /var/log/secure and identify any suspicious activity.
The "Too many authentication failures for user" error can be addressed by properly configuring both the SSH client and server and by increasing awareness of security aspects. It's also crucial to regularly monitor logs and respond to any anomalies that may indicate unauthorized access attempts.
