Permission denied public key with Cap, but I can ssh into github - deployment

Question

So I've been wrestling with Capistrano a lot, and I think I've always got it to deploy.
The issue I'm having now is that doing a cap deploy gives me:
Chintan at mbp in ~/Documents/Work/faxattach on master!
± cap deploy
/Users/Chintan/.rvm/gems/ruby-1.9.3-p0/gems/bundler-1.2.3/lib/bundler/runtime.rb:197: warning: Insecure world writable dir /usr/local/bin in PATH, mode 040777
triggering load callbacks
* 2013-07-03 16:13:56 executing `staging'
triggering start callbacks for `deploy'
* 2013-07-03 16:13:56 executing `multistage:ensure'
* 2013-07-03 16:13:56 executing `deploy'
* 2013-07-03 16:13:56 executing `deploy:update'
** transaction: start
* 2013-07-03 16:13:56 executing `deploy:update_code'
executing locally: "git ls-remote git#github.com:chintanparikh/faxattach.git HEAD"
command finished in 611ms
* executing "git clone -q git#github.com:chintanparikh/faxattach.git /srv/www/faxattach/releases/20130703201357 && cd /srv/www/faxattach/releases/20130703201357 && git checkout -q -b deploy a237b155f1fe4acef23ad4b594749c567a213117 && (echo a237b155f1fe4acef23ad4b594749c567a213117 > /srv/www/faxattach/releases/20130703201357/REVISION)"
servers: ["faxattach-staging-new"]
[faxattach-staging-new] executing command
** [faxattach-staging-new :: out] Permission denied (publickey).
** [faxattach-staging-new :: out] fatal: The remote end hung up unexpectedly
command finished in 1286ms
*** [deploy:update_code] rolling back
* executing "rm -rf /srv/www/faxattach/releases/20130703201357; true"
servers: ["faxattach-staging-new"]
[faxattach-staging-new] executing command
command finished in 572ms
failed: "rvm_path=/usr/local/rvm /usr/local/rvm/bin/rvm-shell 'ruby-1.9.3-p327#faxattach' -c 'git clone -q git#github.com:chintanparikh/faxattach.git /srv/www/faxattach/releases/20130703201357 && cd /srv/www/faxattach/releases/20130703201357 && git checkout -q -b deploy a237b155f1fe4acef23ad4b594749c567a213117 && (echo a237b155f1fe4acef23ad4b594749c567a213117 > /srv/www/faxattach/releases/20130703201357/REVISION)'" on faxattach-staging-new
However, if I manually ssh into my server and then do a ssh -vT git#github.com, it works fine:
faxattach at ip-10-164-71-243 in ~
○ ssh -vT git#github.com
OpenSSH_5.9p1 Debian-5ubuntu1.1, OpenSSL 1.0.1 14 Mar 2012
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug1: Connecting to github.com [204.232.175.90] port 22.
debug1: Connection established.
debug1: identity file /home/faxattach/.ssh/id_rsa type 1
debug1: Checking blacklist file /usr/share/ssh/blacklist.RSA-2048
debug1: Checking blacklist file /etc/ssh/blacklist.RSA-2048
debug1: identity file /home/faxattach/.ssh/id_rsa-cert type -1
debug1: identity file /home/faxattach/.ssh/id_dsa type -1
debug1: identity file /home/faxattach/.ssh/id_dsa-cert type -1
debug1: identity file /home/faxattach/.ssh/id_ecdsa type -1
debug1: identity file /home/faxattach/.ssh/id_ecdsa-cert type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_5.5p1 Debian-6+squeeze1+github12
debug1: match: OpenSSH_5.5p1 Debian-6+squeeze1+github12 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.9p1 Debian-5ubuntu1.1
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 16:27:ac:a5:76:28:2d:36:63:1b:56:4d:eb:df:a6:48
debug1: Host 'github.com' is known and matches the RSA host key.
debug1: Found key in /home/faxattach/.ssh/known_hosts:1
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: Offering RSA public key: /home/faxattach/.ssh/id_rsa
debug1: Server accepts key: pkalg ssh-rsa blen 279
debug1: Authentication succeeded (publickey).
Authenticated to github.com ([204.232.175.90]:22).
debug1: channel 0: new [client-session]
debug1: Requesting no-more-sessions#openssh.com
debug1: Entering interactive session.
debug1: Remote: Forced command: gerve chintanparikh c3:ff:25:e1:30:be:c7:37:51:b5:87:7c:46:dc:c0:c7
debug1: Remote: Port forwarding disabled.
debug1: Remote: X11 forwarding disabled.
debug1: Remote: Agent forwarding disabled.
debug1: Remote: Pty allocation disabled.
debug1: Remote: Forced command: gerve chintanparikh c3:ff:25:e1:30:be:c7:37:51:b5:87:7c:46:dc:c0:c7
debug1: Remote: Port forwarding disabled.
debug1: Remote: X11 forwarding disabled.
debug1: Remote: Agent forwarding disabled.
debug1: Remote: Pty allocation disabled.
debug1: Sending environment.
debug1: Sending env LANG = en_US.UTF-8
debug1: Sending env LC_CTYPE = en_US.UTF-8
debug1: client_input_channel_req: channel 0 rtype exit-status reply 0
debug1: client_input_channel_req: channel 0 rtype eow#openssh.com reply 0
Hi chintanparikh! You've successfully authenticated, but GitHub does not provide shell access.
debug1: channel 0: free: client-session, nchannels 1
Transferred: sent 2816, received 2984 bytes, in 0.1 seconds
Bytes per second: sent 33714.5, received 35725.9
debug1: Exit status 1
Any ideas?

Answer 1

Add this to your config/deploy.rb
set :ssh_options, { :forward_agent => true }
If you're using your own private keys for git, you want to tell Capistrano to use agent forwarding with this command. Agent forwarding can make key management much simpler as it uses your local keys instead of keys installed on the server.
Source: Agent Forwarding Topic.
and make sure the user is not sudo in config/deploy.rb:
set :use_sudo, false
as in the logs you have attached, you are logged in as faxattach ( which is perhaps not sudo).

Answer 2

The ssh connection that fails is made to the server, not to github.
You should check if you can get on the server with this key.
If not you should add the public key to the servers .ssh/authorized_keys.
Also check if the user for the server is correct and exists.