Why is my SSH public key authentication not working?

I just found the following entry in the auth.log file for each failure:

Apr 20 18:57:16 sshd[4021]: reverse mapping checking getaddrinfo for [] failed - POSSIBLE BREAK-IN ATTEMPT!

I cannot find much relivant, just old posts that don't count any more as the "UseDNS" option does not exit in /etc/ssh/sshd_config

Are you sure you set up the keys correctly? Did you copy the idrsa.pub file to your user directory on the server and save it as ".ssh/authorizedkeys"? Is the private key in your local .ssh folder?

@u4ia:

Are you sure you set up the keys correctly?
Yes
@u4ia:

Did you copy the idrsa.pub file to your user directory on the server and save it as ".ssh/authorizedkeys"?
Yes
@u4ia:

Is the private key in your local .ssh folder?
Yes - path /home//.ssh/

Can you provide the output of the following:

ls -la /home//.ssh # run this on the Linode

ls -la /home//.ssh # run this on your local machine

ssh @ -v # run this from your local machine, towards your Linode's user/IP

tail -n20 /var/log/auth.log # And run that on the Linode after the above

• Les

Hi Les,

The info is below… thanks for your help on this mate… I appreciate it.

@akerl:

ls -la /home//.ssh # run this on the Linode

drwxr-xr-x 2 <user><user>4096 Apr 20 18:54 .
drwxr-xr-x 4 <user><user>4096 Apr 20 18:12 ..
-rw-r--r-- 1 <user><user>393 Apr 20 18:54 authorized_keys</user></user></user></user></user></user> 

@akerl:

ls -la /home//.ssh # run this on your local machine

drwx------   2 <user><user>4096 Jun 20  2011 .
drwxr-xr-x 107 <user><user>28672 Apr 20 17:41 ..
-rwx------   1 <user><user>1679 Apr 20 18:30 id_rsa
-rwx------   1 <user><user>393 Apr 20 18:30 id_rsa.pub
-rwx------   1 <user><user>5907 Apr 20 17:37 known_hosts</user></user></user></user></user></user></user></user></user></user> 

ssh @ -v # run this from your local machine, towards your Linode's user/IP

OpenSSH_6.0p1 Debian-3ubuntu1, OpenSSL 1.0.1c 10 May 2012
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug1: Connecting to <linode_ip>[<linode_ip>] port 22.
debug1: Connection established.
debug1: identity file /home/<username>/.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/<username>/.ssh/id_rsa-cert type -1
debug1: identity file /home/<username>/.ssh/id_dsa type -1
debug1: identity file /home/<username>/.ssh/id_dsa-cert type -1
debug1: identity file /home/<username>/.ssh/id_ecdsa type -1
debug1: identity file /home/<username>/.ssh/id_ecdsa-cert type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_5.9p1 Debian-5ubuntu1.1
debug1: match: OpenSSH_5.9p1 Debian-5ubuntu1.1 pat OpenSSH_5*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_6.0p1 Debian-3ubuntu1
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: sending SSH2_MSG_KEX_ECDH_INIT
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ECDSA <host_key_stuff>debug1: Host '<linode_ip>' is known and matches the ECDSA host key.
debug1: Found key in /home/<username>/.ssh/known_hosts:16
debug1: ssh_ecdsa_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,password
debug1: Next authentication method: publickey
debug1: Offering RSA public key: /home/<username>/.ssh/id_rsa
debug1: Server accepts key: pkalg ssh-rsa blen 279
Agent admitted failure to sign using the key.
debug1: Trying private key: /home/<username>/.ssh/id_dsa
debug1: Trying private key: /home/<username>/.ssh/id_ecdsa
debug1: Next authentication method: password</username></username></username></username></linode_ip></host_key_stuff></username></username></username></username></username></username></linode_ip></linode_ip> 

– ENTERED PASSWORD

debug1: Authentication succeeded (password).
Authenticated to <linode_ip>([<linode_ip>]:22).
debug1: channel 0: new [client-session]
debug1: Requesting no-more-sessions@openssh.com
debug1: Entering interactive session.
debug1: Sending environment.
debug1: Sending env LC_MESSAGES = en_US.UTF-8
debug1: Sending env LC_COLLATE = en_US.UTF-8
debug1: Sending env LANG = en_US.UTF-8
debug1: Sending env LC_CTYPE = en_US.UTF-8</linode_ip></linode_ip> 

tail -n20 /var/log/auth.log # And run that on the Linode after the above

Apr 20 21:08:45 <hostname>sshd[7991]: Server listening on :: port 22.
Apr 20 21:08:49 <hostname>sshd[7871]: Received disconnect from <my_ip_address>: 11: disconnected by user
Apr 20 21:08:49 <hostname>sshd[7739]: pam_unix(sshd:session): session closed for user <username>Apr 20 21:08:52 <hostname>sshd[7993]: reverse mapping checking getaddrinfo for <reverse_ip>[<my_ip_address>] failed - POSSIBLE BREAK-IN ATTEMPT!
Apr 20 21:08:55 <hostname>sshd[7993]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost= <my_ip_address>user= <username>Apr 20 21:08:57 <hostname>sshd[7993]: Failed password for <username>from <my_ip_address>port 33801 ssh2
Apr 20 21:09:00 <hostname>sshd[7993]: Accepted password for <username>from <my_ip_address>port 33801 ssh2
Apr 20 21:09:00 <hostname>sshd[7993]: pam_unix(sshd:session): session opened for user <username>by (uid=0)
Apr 20 21:09:20 <hostname>sshd[8125]: Received disconnect from <my_ip_address>: 11: disconnected by user
Apr 20 21:09:20 <hostname>sshd[7993]: pam_unix(sshd:session): session closed for user <username>Apr 20 21:09:26 <hostname>sshd[8225]: reverse mapping checking getaddrinfo for <reverse_ip>[<my_ip_address>] failed - POSSIBLE BREAK-IN ATTEMPT!
Apr 20 21:09:30 <hostname>sshd[8225]: Accepted password for <username>from <my_ip_address>port 33820 ssh2
Apr 20 21:09:30 <hostname>sshd[8225]: pam_unix(sshd:session): session opened for user <username>by (uid=0)
Apr 20 21:11:02 <hostname>sshd[8357]: Received disconnect from <my_ip_address>: 11: disconnected by user
Apr 20 21:11:02 <hostname>sshd[8225]: pam_unix(sshd:session): session closed for user <username>Apr 20 21:11:19 <hostname>sshd[8457]: reverse mapping checking getaddrinfo for <reverse_ip>[<my_ip_address>] failed - POSSIBLE BREAK-IN ATTEMPT!
Apr 20 21:11:59 <hostname>sshd[8457]: Accepted password for <username>from <my_ip_address>port 33831 ssh2
Apr 20 21:11:59 <hostname>sshd[8457]: pam_unix(sshd:session): session opened for user <user>by (uid=0)
Apr 20 21:13:18 <hostname>sudo:     <username>: TTY=pts/0 ; PWD=/home/ <username>; USER=root ; COMMAND=/usr/bin/tail -n20 /var/log/auth.log
Apr 20 21:13:18 <hostname>sudo: pam_unix(sudo:session): session opened for user root by <username>(uid=1000)</username></hostname></username></username></hostname></user></hostname></my_ip_address></username></hostname></my_ip_address></reverse_ip></hostname></username></hostname></my_ip_address></hostname></username></hostname></my_ip_address></username></hostname></my_ip_address></reverse_ip></hostname></username></hostname></my_ip_address></hostname></username></hostname></my_ip_address></username></hostname></my_ip_address></username></hostname></username></my_ip_address></hostname></my_ip_address></reverse_ip></hostname></username></hostname></my_ip_address></hostname></hostname> 

The troublesome line:

Agent admitted failure to sign using the key.

It sounds like your SSH agent doesn't know about your key and for some reason isn't adding it. I'd recommend running 'ssh-add' on your local machine and trying again.

Thanks for that mate… ssh-add did the trick! Appreciate the help