SSH 経由で初めて EC2 にログインします。秘密鍵ファイルを開くことができません。そのため、chmod を 700 に変更しましたが、それでも同じエラーがスローされます。どうすれば修正できるか提案してください。
Macs-MacBook-Pro:~ Macbook$ ssh -v -i ~/.ssh/aug1981.pem ubuntu@ec2-54-200-94-18.us-west-2.compute.amazonaws.com
OpenSSH_6.2p2, OSSLShim 0.9.8r 8 Dec 2011
debug1: Reading configuration data /etc/ssh_config
debug1: /etc/ssh_config line 20: Applying options for *
debug1: Connecting to ec2-54-200-94-18.us-west-2.compute.amazonaws.com [54.200.94.18] port 22.
debug1: Connection established.
debug1: identity file /Users/Macbook/.ssh/aug1981.pem type -1
debug1: identity file /Users/Macbook/.ssh/aug1981.pem-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_6.2
debug1: Remote protocol version 2.0, remote software version OpenSSH_5.9p1 Debian-5ubuntu1
debug1: match: OpenSSH_5.9p1 Debian-5ubuntu1 pat OpenSSH_5*
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-ctr hmac-md5 none
debug1: kex: client->server aes128-ctr hmac-md5 none
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<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: Server host key: RSA 8d:e2:20:42:95:c5:bc:14:42:10:a5:cf:40:d8:d9:fa
debug1: Host 'ec2-54-200-94-18.us-west-2.compute.amazonaws.com' is known and matches the RSA host key.
debug1: Found key in /Users/Macbook/.ssh/known_hosts:2
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: /Users/Macbook/.ssh/aug1981.pem
debug1: could not open key file '/Users/Macbook/.ssh/aug1981.pem': Permission denied
debug1: No more authentication methods to try.
Permission denied (publickey).