Linux – PubKey Authentication not Working

centoslinuxmacssh

I tried setting up PubKey authentication between my Mac and CentOS dedi server, but something is up…

Here's the steps I took:

  ssh-keygen -t rsa

Then

  chmod 700 .ssh/ && chmod 600 .ssh/*

Then

  scp id_rsa.pub root@dedi:~/.ssh/authorized_keys

Then (sorry about all these "Then"'s)

  ssh root@dedi

And what do you know? I get prompted for my password.

Any ideas? Thanks!

EDIT: Here's the output of ssh -v root@dedi:

  SH_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 dedi
  debug1: Connecting to dediserversdomain.com.au.co.net.org.bz [198.100.145.168] port 22.
  debug1: Connection established.
  debug1: identity file /Users/someone/.ssh/id_rsa,~/.ssh/id_dsa type -1
  debug1: identity file /Users/someone/.ssh/id_rsa,~/.ssh/id_dsa-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_5.3
  debug1: match: OpenSSH_5.3 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 (my rsa key)
  debug1: Host 'dediserversdomain.com.au.co.net.org.bz' is known and matches the RSA host key.
  debug1: Found key in /Users/someone/.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,gssapi-keyex,gssapi-with-mic,password
  debug1: Next authentication method: publickey
  debug1: Trying private key: /Users/someone/.ssh/id_rsa,~/.ssh/id_dsa
  debug1: Next authentication method: password
  root@dediserversdomain.com.au.co.net.org.bz's password:

EDIT: Output of stat .ssh and stat .ssh/* from within my dedi:

  File: `.ssh'
  Size: 4096        Blocks: 8          IO Block: 4096   directory
  Device: 801h/2049d    Inode: 1175048     Links: 2
  Access: (0700/drwx------)  Uid: (    0/    root)   Gid: (    0/    root)
  Access: 2014-09-21 11:21:43.000000000 -0400
  Modify: 2014-09-21 10:52:26.000000000 -0400
  Change: 2014-09-21 11:21:49.000000000 -0400

  File: `.ssh/authorized_keys'
  Size: 411         Blocks: 8          IO Block: 4096   regular file
  Device: 801h/2049d    Inode: 1175045     Links: 1
  Access: (0600/-rw-------)  Uid: (    0/    root)   Gid: (    0/    root)
  Access: 2014-09-21 10:52:26.000000000 -0400
  Modify: 2014-09-21 10:52:26.000000000 -0400
  Change: 2014-09-21 11:21:43.000000000 -0400

EDIT: Here's the output of /usr/sbin/sshd -d

  debug1: sshd version OpenSSH_5.3p1
  debug1: read PEM private key done: type RSA
  debug1: private host key: #0 type 1 RSA
  debug1: read PEM private key done: type DSA
  debug1: private host key: #1 type 2 DSA
  debug1: rexec_argv[0]='/usr/sbin/sshd'
  debug1: rexec_argv[1]='-d'
  Set /proc/self/oom_score_adj from 0 to -1000
  debug1: Bind to port 22 on 0.0.0.0.
  Bind to port 22 on 0.0.0.0 failed: Address already in use.
  debug1: Bind to port 22 on ::.
  Bind to port 22 on :: failed: Address already in use.
  Cannot bind any address.

EDIT: Here's the output of grep 'sshd' /var/log/*:
Binary file /var/log/btmp matches
Binary file /var/log/btmp-20140901 matches
/var/log/dovecot-info.log:Aug 08 09:10:03 pop3-login: Info: Disconnected (auth failed, 1 attempts): user=, method=PLAIN, rip=211.43.207.112, lip=198.100.145.168
/var/log/install_rtm.log:rtm hINFO_TCP_LISTEN_IP-0-0-0-0_PORT-22_procname|sshd
/var/log/install_rtm.log:rtm hINFO_TCP_LISTEN_IP-0-0-0-0_PORT-22_cmdline|/usr/sbin/sshd
/var/log/install_rtm.log:rtm hINFO_TCP_LISTEN_IP-0-0-0-0_PORT-22_exe|/usr/sbin/sshd
/var/log/install_rtm.log:rtm hINFO_TCP_LISTEN_IP-0_PORT-22_procname|sshd
/var/log/install_rtm.log:rtm hINFO_TCP_LISTEN_IP-0_PORT-22_cmdline|/usr/sbin/sshd
/var/log/install_rtm.log:rtm hINFO_TCP_LISTEN_IP-0_PORT-22_exe|/usr/sbin/sshd

Best Answer

In /etc/ssh/sshd_config, set LogLevel to DEBUG3, then service sshd restart

tail -F /var/log/secure > /root/tmp.txt: this is a useful way of getting only the logs relating to the test; although you'll get a few old lines beforehand. It will appear to hang (you can put it in the background if you like)

Attempt to auth again (presumably it will fail). Kill the tail -F ... job you started earlier. The reason for the failure will very likely be seen in /root/tmp.txt.

Most of the time its due to a poorly formatted (or line-wrapped) entry in your /root/.ssh/authorized_keys (mind the American English spelling).

Other common reasons:

  • AllowRoot is set to no;
  • PubKeyAuthentication is set to no (mind also RSAAuthentication, which is for SSH version 1 (which should be disabled)

You might also be on the lookout for a Limit stanza which might treat you differently.

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