Amazon EC2 SSH server sent: ( publickey, gssapi-keyex,gssapi-with-mic) - ssh

Question

I get this error message when trying to connect with ssh.
Disconnected: No supported authentication methods available (server sent: publickey,gssapi-keyex,gssapi-with-mic)
I create a instances(cent os), generated my webserver.pem, puttygen imported that and output a ppk
I have seen that it may be a permissions issue with the ~/.ssh on the server but how can i change the permissions on the server without ssh access to the server? Is there another way to connect that i am not aware of? I am quite new to the amazon ec2 stuff.
I am on a windows system right now using putty.

Answer 1

My security groups were incorrect. I remade the instance with the correct security groups

Answer 2

The below steps worked for me.
Edit sshd_config file sudo vi /etc/ssh/sshd_config.
Search for PasswordAuthentication
If it is no, change it to yes. For me it was commented. If so, uncomment it.
Restart sshd service sudo systemctl restart sshd.service
Done.

Answer 3

These are the basic steps generally when working with a public cloud, trying to create a Virtual Machine and connect to it.
Create a Virtual Cloud Network/ Virtual Private Cloud
Create an Internet Gateway and ensure the Route Table for the VCN has the entry to route internet bound traffic (destination 0.0.0.0/0) to the internet gateway
Create a Virtual Machine (Linux in this case), ensure it has a public IP ( VM be created in public subnet ), download the key pair (for example was in PEM format)
Create a Security Group and ensure ingress rule from source : 0.0.0.0/0, protocol: TCP, destination port: 22
Associate the VM with the Security Group at VNIC level at the time of creating the VM or post creation.
From Oracle Cloud documentation -
Just having an internet gateway alone does not expose the instances in
the VCN's subnets directly to the internet. The following requirements
must also be met:
The internet gateway must be enabled (by default, the internet gateway
is enabled upon creation). The subnet must be public. The subnet
must have a route rule that directs traffic to the internet gateway.
The subnet must have security list rules that allow the traffic (and
each instance's firewall must allow the traffic). The instance must >
have a public IP address.
Now connecting to VM using putty, basically you are doing a :
ssh user#ip_address —i private_key
a. Use puttygen and load the private PEM key that you downloaded. Once successfully imported, save the private key (optionally with a passphrase) as PPK in your local machine ( for example "your_pvt_key_name.ppk" )
b. Use putty to connect to the VM's public IP. Ensure in putty when connecting to the VM that private key is provided for authentication. In the section Connection->SSH->Auth, browse for the "your_pvt_key_name.ppk" and then go back to the Session and "Open" the VM. If the VM is on public subnet with correct route table entry, you should see the login screen. In case the VM is not available on internet, it wont connect !
c. Once you see the login screen most important and which is the probable cause of the above error, login with correct user name, such as "ec2-user" in AWS or "opc" in OCI. Using an incorrect user name results in this error.
No supported authentication methods available (server sent: publickey,gssapi-keyex,gssapi-with-mic)