diagnostic cap deploy permission denied public key

Problem:

xxxxx@xxxxx:~/RubyProjects/xxxxx$ bundle exec cap xxxxx deploy:migrations
/usr/local/rvm/gems/ree-1.8.7-2012.02@global/gems/bundler-1.1.4/lib/bundler/runtime.rb:211: warning: Insecure world writable dir /usr/local/rvm/gems in PATH, mode 042777
/usr/local/rvm/gems/ree-1.8.7-2012.02@global/gems/bundler-1.1.4/lib/bundler/runtime.rb:211: warning: Insecure world writable dir /usr/local/rvm/gems in PATH, mode 042777
  * executing `xxxxx'
    triggering start callbacks for `deploy:migrations'
  * executing `multistage:ensure'
  * executing `eighties_bands:ensure'
  * executing `deploy:migrations'
  * executing `deploy:update_code'
    updating the cached checkout on all servers
    executing locally: "git ls-remote git@xxxxx.unfuddle.com:xxx/xxxxx.git xxxxx-4"
    command finished in 4746ms
  * executing "if [ -d /home/xxxxx/deploy/shared/cached-copy ]; then cd /home/xxxxx/deploy/shared/cached-copy && git fetch -q origin && git reset -q --hard b40a43e351c2107de5c6bc8dae0c70de86465305 && git clean -q -d -x -f; else git clone -q  git@xxx.unfuddle.com:xxx/xxxxx.git /home/xxxxx/deploy/shared/cached-copy && cd /home/xxxxx/deploy/shared/cached-copy && git checkout -q -b deploy b40a43e351c2107de5c6bc8dae0c70de86465305; fi"
    servers: ["115.160.152.28"]
    [115.160.152.28] executing command
 ** [115.160.152.28 :: err] Permission denied (publickey).
 ** [115.160.152.28 :: err] fatal: The remote end hung up unexpectedly
    command finished in 13024ms
failed: "sh -c 'if [ -d /home/xxxxx/deploy/shared/cached-copy ]; then cd /home/xxxxx/deploy/shared/cached-copy && git fetch -q origin && git reset -q --hard b40a43e351c2107de5c6bc8dae0c70de86465305 && git clean -q -d -x -f; else git clone -q  git@xxx.unfuddle.com:xxx/xxxxx.git /home/xxxxx/deploy/shared/cached-copy && cd /home/xxxxx/deploy/shared/cached-copy && git checkout -q -b deploy b40a43e351c2107de5c6bc8dae0c70de86465305; fi'" on 115.160.152.28

Reason:
  git login failed on target machine.

Checkings:
ssh -v git@xxx.unfuddle.com

• Check this on deployment machine and target server
• If success, should see this: Authentication succeded (publickey).
• If denied, will see this: debug1: Authentications that can continue: publickey
  • This means the connection to git server is denied.

Solution:
On deployment machine,

• ForwardAgent yes (.ssh/config)
• Check if ssh-agent is running
• ps aux | grep ssh
• Add key to ssh:
• ssh-add ~/.ssh/id_rsa
• Check key:
• ssh-add -l
• Done