AWS SSH connection error: Permission denied (publickey)

Question

Im trying to connect to my EC2 instance with SSH and Iḿ getting crazy. I have read this post and tried all user combinations:

AWS ssh access 'Permission denied (publickey)' issue

Its still not working for me. Any idea what am I missing?

  roberto@ubuntu:~/keys$ ssh -v -i ec2-key-pair.pem [email protected]
OpenSSH_6.6, OpenSSL 1.0.1f 6 Jan 2014
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug1: Connecting to ec2-54-72-242-0.eu-west-1.compute.amazonaws.com [54.72.242.0] port 22.
debug1: Connection established.
debug1: identity file ec2-key-pair.pem type -1
debug1: identity file ec2-key-pair.pem-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_6.6p1 Ubuntu-2ubuntu1
debug1: Remote protocol version 2.0, remote software version OpenSSH_6.2
debug1: match: OpenSSH_6.2 pat OpenSSH* compat 0x04000000
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-ctr [email protected] none
debug1: kex: client->server aes128-ctr [email protected] none
debug1: sending SSH2_MSG_KEX_ECDH_INIT
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ECDSA e4:06:ee:a5:a5:d2:97:5f:0f:b7:06:5e:f2:b3:da:26
debug1: Host 'ec2-54-72-242-0.eu-west-1.compute.amazonaws.com' is known and matches the ECDSA host key.
debug1: Found key in /home/roberto/.ssh/known_hosts:3
debug1: ssh_ecdsa_verify: signature correct
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: Roaming not allowed by server
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey
debug1: Next authentication method: publickey
debug1: Trying private key: ec2-key-pair.pem
debug1: key_parse_private2: missing begin marker
debug1: read PEM private key done: type RSA
debug1: Authentications that can continue: publickey
debug1: No more authentication methods to try.
Permission denied (publickey).

UPDATE: 

According to @aldanux suggestions:

    roberto@ubuntu:~/keys$ ssh-keygen -R 54.72.242.0
# Host 54.72.242.0 found: line 4 type ECDSA
/home/roberto/.ssh/known_hosts updated.
Original contents retained as /home/roberto/.ssh/known_hosts.old
roberto@ubuntu:~/keys$ ssh -i ec2-key-pair.pem [email protected]
Warning: Permanently added the ECDSA host key for IP address '54.72.242.0' to the list of known hosts.
Permission denied (publickey).

Answer 1

You are probably logging in as the wrong user. If it's a Ubuntu instance the command would be:

ssh -v -i ec2-key-pair.pem [email protected]

Answer 2

While not specific to AWS, this unhelpful error message

debug1: key_parse_private2: missing begin marker

will occur under a handful of obscure scenarios, such as when the ownership (or the permissions) on the SSH user's home directory are incorrect on the remote machine.

The best way to troubleshoot this and similar obscure messages is to examine the authorization log on the remote machine, provided you have access, as it will usually pinpoint the problem. On Debian and Ubuntu systems, this is most easily accomplished with tail (use sudo as appropriate):

tail -f -n 80 /var/log/auth.log

In my particular case, I found

Authentication refused: bad ownership or modes for directory /var/www

Perfectly accurate and concise: the owner:group was set to daemon:daemon when it should have been www-data:www-data (this was on a Ubuntu machine that must have had some other web-server installed in the past).