PuTTY: No supported authentication methods available

Today I got again this error message when trying to connect PuTTY to my VM: “No supported authentication methods available”:

This time I decided to write down exactly what I do to get rid of it. Here it is:

  • call puttygen, generate a public/private key pair:

  • copy the blue part to the clipboard using CTRL_C

  • save the private key as private.ppk, the public one as key.pub.

  • Log in to your VM one last time without putty. In my case, I click on “SSH” in the browser:

  • a shell opens up. Note the user name. Look at this shell:
Last login: Mon Jun  6 09:10:40 2022 from
  • in the above example, the user name is thorsten
  • add the key to authorized_keys:
thorsten@guacamole-2:~$ cd .ssh
thorsten@guacamole-2:~/.ssh$ cat >>authorized_keys
  • You still have the key copied to the clipboard, right? Right-click into the console to paste it. Type CTRL_D to end the input. Use vi to change rsa-key-220604 to your user name.
  • Now start putty, enter as session thorsten@my-domain, (my-domain as example for your hostname and domain) and select connection -> SSH -> Auth, add the private key file for authentication, then click open:

Now putty opens without the need to enter a password :)

Next step: Automation

This step only works if you have set os_login=false. You can have Google add your public keys to the VMs' authorized_keys files. To do this, search Metadata and click on it:

Then, select SSH keys and paste the ssh key from clipboard into a line.

Click on Save and watch that the keys got added (to /home/thorsten/.ssh/authorized_keys in this example).


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