AWS - Disconnected : No supported authentication m

Question

SSH to my AWS server just broke for both Putty and Filezilla. I'm making some effort for this post to be a comprehensive troubleshooting list, so if you share links to other stack overflow pages, I'll edit them into the question.

Disconnected : No supported authentication methods available (server sent :publickey)

The error is familiar from when I set up the connection almost a year ago. If you're setting up AWS SSH for the first time, these address the most common problems:

• Wrong username: Disconnected : No supported authentication methods available (server sent :publickey)
• Incorrect .ppk file: Unable to connect to amazon server using putty

However, the only thing I could think that would impact a previously working system is:

• Wrong IP: Restarting an AWS instance (or creating an image) is not guaranteed to keep the same IP address. This would obviously have to be updated in putty.

What other possibilities are there?

Solution to this one (per the accepted post below) is that for AWS EC2 all 3 of these need to have proper permissions (777 not ok for any of these). Here's one example that works:

/home/ec2-user/ - 700
/home/ec2-user/.ssh/ - 600
/home/ec2-user/.ssh/authorized_keys - 600

/var/log/secure will tell you which one is throwing an error, consult this video tutorial to get access if you're completely locked out: http://d2930476l2fsmh.cloudfront.net/LostKeypairRecoveryOfLinuxInstance.mp4

Answer 1

in most cases, got no authentication method error when using the wrong username for logging in. But I do find something else if you still struggle with connection issue and you have tried all the options above.

I created couple Linux VM and try to reproduce such connection issue, one thing I found is, when AWS asked you name your key pair, DO NOT user blank space (" ") and dot (".") in key pair name, even AWS actually allow you to do so.

ex. when I named the key pair as "AWS.FREE.LINUX", connection always be refused. When I named as "AWS_FREE_LINUX", everything works fine.

Hope this will help a little bit.

Answer 2

Comprehensive answer is here: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/putty.html

Your problem can be related to incorrect login which varies depending on AMIs. Use following logins on following AMIs:

• ubuntu or root on ubuntu AMIs
• ec2-user on Amazon Linux AMI
• centos on Centos AMI
• debian or root on Debian AMIs
• ec2-user or fedora on Fedora
• ec2-user or root on: RHEL AMI, SUSE AMI, other ones.

If you are using OS:

• Windows - get PEM key from AWS website and generate PPK file using PuttyGen. Then use Putty to use the PPK (select it using left-column: Connection->SSH->Auth: Private key for authorization)
• Linux - run: ssh -i your-ssh-key.pem login@IP-or-DNS

Good luck.

Answer 3

During ssh session my connection broke, since then I cannot ssh my SRV, I had started a new instance, and I'm able to ssh the new instance (with the same key).

I mounted the old volume to the new machine, and check the .ssh/authorized_key and couldn't find any problem with permission or content.