title: SSH to EC2 but get Permission denied (publickey)
body: <p>I generated the key-pair by EC2-Console, and then store it in ~/.ssh/iForests_ABetADay.pem.<br>
  After that, chmod 400 iForests_ABetADay.pem, and ssh -i iForests_ABetADay.pem ubuntu@46.51.244.48 -v.<br>
  I did login yesterday, but now the error message I got is:<br>
  (Google a lot, but still can not find out a way to solve it...)<br></p>
  
  <pre><code>OpenSSH_5.6p1, OpenSSL 0.9.8r 8 Feb 2011
  debug1: Reading configuration data /etc/ssh_config
  debug1: Applying options for *
  debug1: Connecting to 46.51.244.48 [46.51.244.48] port 22.
  debug1: Connection established.
  debug1: identity file iForests_ABetADay.pem type -1
  debug1: identity file iForests_ABetADay.pem-cert type -1
  debug1: Remote protocol version 2.0, remote software version OpenSSH_5.8p1 Debian-1ubuntu3
  debug1: match: OpenSSH_5.8p1 Debian-1ubuntu3 pat OpenSSH*
  debug1: Enabling compatibility mode for protocol 2.0
  debug1: Local version string SSH-2.0-OpenSSH_5.6
  debug1: SSH2_MSG_KEXINIT sent
  debug1: SSH2_MSG_KEXINIT received
  debug1: kex: server-&gt;client aes128-ctr hmac-md5 none
  debug1: kex: client-&gt;server aes128-ctr hmac-md5 none
  debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024&lt;1024&lt;8192) sent
  debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
  debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
  debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
  debug1: Host '46.51.244.48' is known and matches the RSA host key.
  debug1: Found key in /Users/iforests/.ssh/known_hosts:17
  debug1: ssh_rsa_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: iForests_ABetADay.pem
  debug1: read PEM private key done: type RSA
  debug1: Authentications that can continue: publickey
  debug1: No more authentication methods to try.
  Permission denied (publickey).
  </code></pre>