Cannot connect using keys with Ruby and net/ssh

I'm having trouble connecting via ssh from ruby using the 'net-ssh' gem, getting Net::SSH::AuthenticationFailed. The code is below

require 'net/ssh'
keys = ["path_to_private_key"]
Net::SSH.start('host', 'user',:keys => keys, :verbose => :debug) do |ssh|
  #ssh code

end

Using ssh directly from the command line works:

ssh -i <path_to_private_key> user@host

Do I have the the ssh API wrong? I have tried both 'user@host' and just 'user' as the username with the same result.

Here is the debugging output:

D, [2011-07-26T19:42:00.135148 #3511] DEBUG -- net.ssh.transport.session[140b040]: establishing connection to host:22
D, [2011-07-26T19:42:00.164190 #3511] DEBUG -- net.ssh.transport.session[140b040]: connection established
I, [2011-07-26T19:42:00.164344 #3511]  INFO -- net.ssh.transport.server_version[140a3fc]: negotiating protocol version
D, [2011-07-26T19:42:00.192092 #3511] DEBUG -- net.ssh.transport.server_version[140a3fc]: remote is `SSH-2.0-OpenSSH_5.3p1 Debian-3ubuntu3'
D, [2011-07-26T19:42:00.192177 #3511] DEBUG -- net.ssh.transport.server_version[140a3fc]: local is `SSH-2.0-Ruby/Net::SSH_2.1.4 x86_64-linux'
D, [2011-07-26T19:42:00.212348 #3511] DEBUG -- tcpsocket[140aaf0]: read 784 bytes
D, [2011-07-26T19:42:00.212461 #3511] DEBUG -- tcpsocket[140aaf0]: received packet nr 0 type 20 len 780
I, [2011-07-26T19:42:00.212515 #3511]  INFO -- net.ssh.transport.algorithms[13e9058]: got KEXINIT from server
I, [2011-07-26T19:42:00.212604 #3511]  INFO -- net.ssh.transport.algorithms[13e9058]: sending KEXINIT
D, [2011-07-26T19:42:00.212698 #3511] DEBUG -- tcpsocket[140aaf0]: queueing packet nr 0 type 20 len 556
D, [2011-07-26T19:42:00.212741 #3511] DEBUG -- tcpsocket[140aaf0]: sent 560 bytes
I, [2011-07-26T19:42:00.212771 #3511]  INFO -- net.ssh.transport.algorithms[13e9058]: negotiating algorithms
D, [2011-07-26T19:42:00.212859 #3511] DEBUG -- net.ssh.transport.algorithms[13e9058]: negotiated:
* kex: diffie-hellman-group-exchange-sha1
* host_key: ssh-rsa
* encryption_server: aes128-cbc
* encryption_client: aes128-cbc
* hmac_client: hmac-sha1
* hmac_server: hmac-sha1
* compression_client: none
* compression_server: none
* language_client: 
* language_server: 
D, [2011-07-26T19:42:00.212889 #3511] DEBUG -- net.ssh.transport.algorithms[13e9058]: exchanging keys
D, [2011-07-26T19:42:00.212998 #3511] DEBUG -- tcpsocket[140aaf0]: queueing packet nr 1 type 34 len 20
D, [2011-07-26T19:42:00.213033 #3511] DEBUG -- tcpsocket[140aaf0]: sent 24 bytes
D, [2011-07-26T19:42:00.292238 #3511] DEBUG -- tcpsocket[140aaf0]: read 152 bytes
D, [2011-07-26T19:42:00.292389 #3511] DEBUG -- tcpsocket[140aaf0]: received packet nr 1 type 31 len 148
D, [2011-07-26T19:42:00.297526 #3511] DEBUG -- tcpsocket[140aaf0]: queueing packet nr 2 type 32 len 140
D, [2011-07-26T19:42:00.297627 #3511] DEBUG -- tcpsocket[140aaf0开发者_运维百科]: sent 144 bytes
D, [2011-07-26T19:42:00.321754 #3511] DEBUG -- tcpsocket[140aaf0]: read 720 bytes
D, [2011-07-26T19:42:00.321909 #3511] DEBUG -- tcpsocket[140aaf0]: received packet nr 2 type 33 len 700
D, [2011-07-26T19:42:00.326688 #3511] DEBUG -- tcpsocket[140aaf0]: queueing packet nr 3 type 21 len 20
D, [2011-07-26T19:42:00.326793 #3511] DEBUG -- tcpsocket[140aaf0]: sent 24 bytes
D, [2011-07-26T19:42:00.326927 #3511] DEBUG -- tcpsocket[140aaf0]: received packet nr 3 type 21 len 12
D, [2011-07-26T19:42:00.327325 #3511] DEBUG -- net.ssh.authentication.session[1475c10]: beginning authentication of `user@host'
D, [2011-07-26T19:42:00.327519 #3511] DEBUG -- tcpsocket[140aaf0]: queueing packet nr 4 type 5 len 28
D, [2011-07-26T19:42:00.327604 #3511] DEBUG -- tcpsocket[140aaf0]: sent 52 bytes
D, [2011-07-26T19:42:00.461124 #3511] DEBUG -- tcpsocket[140aaf0]: read 52 bytes
D, [2011-07-26T19:42:00.461199 #3511] DEBUG -- tcpsocket[140aaf0]: received packet nr 4 type 6 len 28
D, [2011-07-26T19:42:00.461260 #3511] DEBUG -- net.ssh.authentication.session[1475c10]: trying publickey
D, [2011-07-26T19:42:00.461370 #3511] DEBUG -- net.ssh.authentication.agent[1470800]: connecting to ssh-agent
E, [2011-07-26T19:42:00.461423 #3511] ERROR -- net.ssh.authentication.agent[1470800]: could not connect to ssh-agent
D, [2011-07-26T19:42:00.461521 #3511] DEBUG -- net.ssh.authentication.methods.publickey[1470bfc]: trying publickey (d7:62:48:07:23:1d:c0:de:80:0d:27:a3:ab:92:72:be)
D, [2011-07-26T19:42:00.461610 #3511] DEBUG -- tcpsocket[140aaf0]: queueing packet nr 5 type 50 len 364
D, [2011-07-26T19:42:00.461648 #3511] DEBUG -- tcpsocket[140aaf0]: sent 388 bytes
D, [2011-07-26T19:42:00.486881 #3511] DEBUG -- tcpsocket[140aaf0]: read 68 bytes
D, [2011-07-26T19:42:00.487057 #3511] DEBUG -- tcpsocket[140aaf0]: received packet nr 5 type 51 len 44
D, [2011-07-26T19:42:00.487186 #3511] DEBUG -- net.ssh.authentication.session[1475c10]: allowed methods: publickey,password
D, [2011-07-26T19:42:00.487261 #3511] DEBUG -- net.ssh.authentication.session[1475c10]: trying password
E, [2011-07-26T19:42:00.487346 #3511] ERROR -- net.ssh.authentication.session[1475c10]: all authorization methods failed (tried publickey, password)

Thanks

$ ssh-keygen -t rsa    
$ ssh-copy-id -i ~/.ssh/id_dsa.pub user@machine
$ ssh user@machine

require 'net/ssh'
require 'logger'

Net::SSH.start(
  'host', 'user',
  :host_key => "ssh-rsa",
  :encryption => "blowfish-cbc",
  :keys => [ "~/.ssh/id_rsa.pub" ],
   :compression => "zlib"
 ) do |session|
   ...
end

That must help you!

Please see your error message

 E, [2011-07-26T19:42:00.461423 #3511] ERROR -- net.ssh.authentication.agent[1470800]: could not connect to ssh-agent

 could not connect to ssh-agent

Notice the E denoting the error.