Why do I get “Permission denied (publickey)” when trying to SSH from local Ubuntu to a Amazon EC2 server?

Question

I have an instance of an application running in the cloud on Amazon EC2 instance, and I need to connect it from my local Ubuntu. It works fine on one of local ubuntu and also laptop. I got message "Permission denied (publickey)" when trying to access SSH to EC2 on another local Ubuntu. It's so strange to me.

I'm thinking some sort of problems with security settings on the Amazon EC2 which has limited IPs access to one instance or certificate may need to regenerate.

Does anyone know a solution?

Answer 1

The first thing to do in this situation is to use the -v option to ssh, so you can see what types of authentication is tried and what the result is. Does that help enlighten the situation?

In your update to your question, you mention "on another local Ubuntu". Have you copied over the ssh private key to the other machine?

Answer 2

i received this error, because i forgot to add -l option. my local username was not the same as on the remote system.

this does not answer your question, but i got here looking for my problem ;]

Answer 3

As it hasn't been explicitly mentioned, sshd is by default very strict on premissions on for the authorized_keys files. So, if authorized_keys is writable for anybody other than the user or can be made writable by anybody other than the user, it'll refuse to authenticate (unless sshd is configured with StrictModes no)

This will not show up with ssh -v, it'll show up in the logs emitted by sshd (typically put in /var/log/secure or /var/log/auth.log, depends on distro and syslogd configuration).

From man sshd(8):

 ~/.ssh/authorized_keys
         Lists the public keys (RSA/DSA) that can be used for logging in
         as this user.  The format of this file is described above.  The
         content of the file is not highly sensitive, but the recommended
         permissions are read/write for the user, and not accessible by
         others.

         If this file, the ~/.ssh directory, or the user's home directory
         are writable by other users, then the file could be modified or
         replaced by unauthorized users.  In this case, sshd will not
         allow it to be used unless the StrictModes option has been set to
         “no”.

Answer 4

I got this message on a new instance based off the Ubuntu AMI. I was using the -i option to provide the PEM but it was still showing the "Permission denied (publickey)".

My problem was that I wasn't using the correct user. By running the ssh with ubuntu@ec2... it worked like normal.

Answer 5

Greg's answer explains how to trouble shoot it better, however the actual issue is that you have an ssh key set on one side of the transaction (the client), which is attempting public key authentication rather than password based authentication. As you don't have the corresponding public key on the EC2 instance, this won't work.

Answer 6

Check your */etc/ssh/sshd_config* file. There, find the line which says

PasswordAuthentication no

That line needs to be modified to say yes instead of no. Also, restart the sshd server afterwards.

sudo /etc/init.d/ssh restart

Answer 7

Something that's easier to read than ssh -i (in my opinion of course), is tail -f /var/logs/auth.log. That should be run on the server you are trying to connect to, while attempting to connect, and will show errors in plain text.

This helped me solve my issue:

User [username] from xx.yy.com not allowed because none of user's groups are listed in AllowGroups

Answer 8

Strangely, my problem turned out to be that the server had been restarted and it was issued a new DNS name. I was using the old DNS name. I know this sounds stupid but it took me a while to figure this out.

Answer 9

Perhaps not relevant to the current poster, but might help others who find this when searching for answers to similar situations. Instead of letting Amazon generate the ssh keypair, I recommend uploading your own, standard, default public ssh key to Amazon and specifying that when you run an EC2 instance.

This lets you drop the "-i" type syntax in ssh, use rsync with standard options, and also lets you use the same ssh key across all EC2 regions.

I wrote an article about this process here:

Uploading Personal ssh Keys to Amazon EC2
http://alestic.com/2010/10/ec2-ssh-keys

Answer 10

If you're trying to connect to a CyanogenMod phone running Dropbear, you should run the following lines to make sure everything is all permission'd right:

chmod 600 /data/dropbear/.ssh/authorized_keys
chmod 755 /data/dropbear/ /data/dropbear/.ssh

This fixed it for me, otherwise nothing can connect.

Answer 11

I was having the same problem even though I was supposedly following all the steps including

$ ec2-authorize default -p 22

However, I had started my instance in us-west-1 region. So the above command should also specify that.

$ ec2-authorize default -p 22 --region us-west-1

After this command I was able to ssh into the instance. I spent a little while before I realized the issue and hope this post helps others.

Answer 12

I had the same problem, and after trying tons of solutions which failed to work i opened the SSH port on my router's firewall (my router's firewall control panel is a mess, so it's hard to tell what's going on). Anyway, that fixed it :)

Super bloody annoying that the error you get is Permission Denied, implying that there was some kind of connection made, grr.

Answer 13

If you're using CentOS 5, you may want to set "StrictModes no" in /etc/ssh/sshd_config. I'm sharing /home directory using NIS/NFS, and I set all the permissions correctly, but it always prompted me with the password. After I set "StrictModes no", the problem disappeared!