After you determine when to troubleshoot an issue instead of migrating or redeploying, you can identify and resolve specific SSH errors based on which phase of a successful SSH connection you need to debug.
Once the connection is established and the protocol is initiated to communicate securely, the system can then verify the user connecting to the system. A wide variety of authentication mechanisms are supported. This walkthrough will cover the two most common: password and private/public key pair.
To troubleshoot SSH issues, you will need to make sure your Droplet is responding normally from the Droplet console with a working network configuration. Before troubleshooting SSH, you should always check your cloud panel for ongoing issues in the region impacting your Droplet, the hypervisor status, and the state of the Droplet through the Droplet console.
Below are some common SSH authentication errors you might encounter.
Note: If you assigned an SSH key when creating your Droplet,
PasswordAuthentication is disabled for your Droplet, and you will need to use your SSH key to login.
You might see these errors in both PuTTY and OpenSSH clients when attempting to log in to a Droplet with a password:
email@example.com's password: Permission denied (publickey,password).
firstname.lastname@example.org's password: Access denied Server sent disconnect message type 2 (protocol error): "Too many authentication failures for root"
This indicates that authentication has failed and can be caused by a number of issues. Here are some steps you can take to troubleshoot this issue:
This login method uses cryptographic keys to authenticate a user. You can learn more about how SSH keys work in our SSH Essentials tutorial.
This is the only authentication method supported when you create a Droplet using SSH keys. You can enable password authentication in the SSH service configuration file once you successfully login with your SSH key.
You might see an error like this:
Permission denied (publickey).
Disconnected: No supported authentication methods available (server sent: publickey)
Many of the most common issues regarding key-based authentication are caused by incorrect file permissions or ownership. Here are some steps you can take to troubleshoot this issue:
authorized_keysfile and the private key itself have the correct permissions and ownership.
authorized_keysfile contains the matching public key. You will want to check that your public key is added to the Droplet.
If you are not able to recover access to the console, this could indicate issues with the file system that impact the authentication mechanism or configuration issues within the PAM subsystem. This would also impact attempts to reset the root password for the Droplet and log in through the console.
From the console, you’ll see this login prompt:
Ubuntu 14.04.4 LTS server tty1 server Login: Password:
But when you enter the correct password, you might get this error:
After a password reset, you’ll receive a prompt like this:
You are required to change your password immediately (root enforced) Changing password for root. (Current) UNIX Password:
You must re-enter the current password. If your connection closes immediately, then you may have made a mistake re-entering the current password, so try again.
On success, you will then be prompted to enter the new password twice:
Enter new UNIX password: Retype new UNIX password:
However, if after entering the same new password twice your session restarts (i.e., you’re sent back to the prompt for login again) or you see an error, it typically means that there’s a problem with one of the critical files used in managing your authentication data.
In this scenario, you will want to consider using the recovery environment to prepare your data for re-deployment or attempt to resolve the issues with the PAM configuration or file system.
Below are some troubleshooting methods and solutions to common SSH authentication errors.
If you use verbose SSH client output or logging, check that the message outlining authentication methods includes
publickey in the list:
debug1: Authentications that can continue: publickey,password
If the message doesn’t include the authentication method you want to use, take a look at the
/etc/ssh/sshd_config configuration file. It’s a common error to accidentally set the
PasswordAuthentication value to
without-password when logging in as root.
Ensure that the appropriate configuration for your login method is set, then restart the service.
The OpenSSH server and client require strict permissions on the key files used.
Both the host and the client should have the following permissions and owners:
~./sshpermissions should be
~./sshshould be owned by your account
~/.ssh/authorized_keyspermissions should be
~/.ssh/authorized_keysshould be owned by your account
Client environments should additionally have the following permissions and owners:
~/.ssh/configpermissions should be
~/.ssh/id_*permissions should be
These changes may need to be made through the Droplet console.
If you forget which private key matches which public key, OpenSSH tools and the PuTTY suite of applications provide a way to generate a public key from a private key. You can use that to compare the contents of the
~/.ssh/authorized_keys file on your Droplets.
To get a public key from a private key in an OpenSSH environment, use the
ssh-keygen command as follows, specifying the path of the private key. By default, it’s
ssh-keygen -y -f ~/.ssh/id_rsa
This will generate a public key, like this:
In PuTTY environments, the
PuTTYgen.exe command will load a GUI where you can use the Load action to import the private key file. In PuTTY, this is normally stored in
.ppk format, and you need to know the location of the file.
Once you import the key, the window will contain a Public key for pasting into OpenSSH authorized_keys file section with a similar-looking sequence. If you select that text and paste it into a file, it will collapse the
+ characters that it shows, and produce the public key.
ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQCfBiMwCU1xoVVp0VbSYV3gTDV/jB57IHdILQ8kJ2622//Lmi4gDPlxA6HXVKq8odkGD/5MjqUw85X2rwEbhoBul74+LCToYJvvvBaDPCgg5z1icCKIJ1m/LJBrGNqPKCgqFWu0EH4/EFP2XIQqWqX1BZtJu/2YWrTr+xFOE/umoYmOd+t3dzQqMsv/2Aw+WmA/x/B9h+41WrobDgCExYNLPYcD0PO7fpsa8CcrZCo+TUWCe7MgQQCSM6WD4+PuYFpUWGw3ILTT51bOxoUhAo19U8B2QqxbMwZomzL1vIBhbUlbzyP/xgePTUhEXROTiTFx8W9yetDYLkfrQI8Q05+f imported-openssh-key
You can ignore the comment following the public key (which is
imported-openssh-key) as it may differ from your generated key comment.
In both cases, make sure this public key is included as a line in your
~/.ssh/authorized_keys file on the server, and add it if not.
On systems with with OpenSSH 7 (FreeBSD and CoreOS, by default), any older DSA-based keys will not be supported for authentication. The
ssh-dss key is considered weak and using more modern key algorithms is strongly recommended.
Consequently, the best solution is to generate more modern keys and update your existing hosts to allow the new keys. However, as a workaround, you can set the
PubkeyAcceptedKeyTypes directive to
+ssh-dss in your
For steps on successfully setting up key based authentication, the following guides are great references:
If you need further help authenticating via SSH, you can open a support ticket. Make sure to include:
Including all the above diagnostic information and clarifying where you are encountering the issue when trying to connect can help us quickly get up to speed with where your need on the issue is.