Why password authentication is not allowed?

Question

My ssh seems only accept public key authentication now. Even if I'm sure that "PasswordAuthentication" is yes in my /etc/ssh/ssh_config. Here is my ssh log. I wanna know why the password authentication is not allowed in my ssh? P.S: I can force ssh to use password authentication by adding "-o PubkeyAuthentication=no" in the command line.

markz@markz-hp6200:~$ ssh -l lab 10.19.170.114 -v
OpenSSH_5.9p1 Debian-5ubuntu1, OpenSSL 1.0.1 14 Mar 2012
debug1: Reading configuration data /home/markz/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug1: Connecting to 10.19.170.114 [10.19.170.114] port 22.
debug1: Connection established.
debug1: identity file /home/markz/.ssh/id_rsa type -1
debug1: identity file /home/markz/.ssh/id_rsa-cert type -1
debug1: identity file /home/markz/.ssh/id_dsa type -1
debug1: identity file /home/markz/.ssh/id_dsa-cert type -1
debug1: identity file /home/markz/.ssh/id_ecdsa type -1
debug1: identity file /home/markz/.ssh/id_ecdsa-cert type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_5.9p1 Debian-5ubuntu1
debug1: match: OpenSSH_5.9p1 Debian-5ubuntu1 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.9p1 Debian-5ubuntu1
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 d5:c0:00:1b:bf:54:56:a0:c6:68:6f:62:a4:1a:e3:e1
debug1: Host '10.19.170.114' is known and matches the ECDSA host key.
debug1: Found key in /home/markz/.ssh/known_hosts:10
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: markz@markz-hp6200
debug1: Authentications that can continue: publickey,password
debug1: Offering RSA public key: markz@markz-hp6200
debug1: Authentications that can continue: publickey,password
debug1: Offering RSA public key: markz@markz-hp6200
debug1: Authentications that can continue: publickey,password
debug1: Offering RSA public key: markz@markz-hp6200
debug1: Authentications that can continue: publickey,password
debug1: Offering RSA public key: markz@markz-desktop
debug1: Authentications that can continue: publickey,password
debug1: Offering RSA public key: markz@markz-desktop
Received disconnect from 10.19.170.114: 2: Too many authentication failures for lab

Srini

Answer 1

The SSH client doesn't have a change to even try password authentication because all authentication attempts are used for your public keys.

Removed unused public keys, add something like

Host * PubkeyAuthentication=no

to ~/.ssh/config or actually use public key authentication by adding a public key to ~/.ssh/authorized_keys on the server side.

Headdress

Thanks. Yes, I have some public keys in my ~/.ssh directory, but according to my understanding, ssh should not use them to try to authenticate except id_rsa.pub. But anyway, I think your suggestion is right, I'll try that. – Srini

By adding "Host * PubkeyAuthentication=no", I can login into server which requires password authentication but can't login server which requires pubkey. :( – Srini

Alright, I figured it out. Need to add "PubkeyAuthentication yes" for every site which requires pubkey authentication. – Srini

Which you by the way can also do in ~/.ssh/config with the Host directive (could not derive whether you did that or whether you would just add it as an option to the command line every time). – Headdress

Answer 2

I am afraid you have too many keys available in your ~/.ssh.

ssh seems to try to use first every key available, but the target machine will only accept 5 authentication requests, so there is no chance to attempt a password authentication.

Move or remove some unused keys so that you have less than 5 keys in your "ssh-add -l".

Topdrawer

Answer 3

I also found out that this error pops up when you don't have the same host name set up as the server reports itself, even though your account is valid and ssh public key's permissions are correctly set up.

So for e.g. you have overridden the hostname in your /etc/hosts locally, giving an alias which is different to what the actual hostname is of the remote SSH server.

XX.XX.YY.YY   host.correct.domain   hostalias

If you are trying to ssh using the hostname as hostalias, the remote SSH server refuses public key authentication, because its hostname is host.correct.domain . This happens on OpenSSH v4.3 server version.

Hope this helps.

Ariannearianrhod

Answer 4

I had this issue but without too many public keys. The server never offered password authentication, also not on the first try. I had set PasswordAuthentication yes on the server and restarted ssh.service.

The problem was that the 24.04 Ubuntu Server for Raspberry Pi includes a second configuration file with 1 line, precisely the thing you need to enable in order to use ssh-copy-id (typing the 16-character random password into the physical console and comparing the ssh fingerprint is annoying enough without also having to type over an ssh public key before being able to remotely access it):

$ cat /etc/ssh/sshd_config.d/50-cloud-init.conf
PasswordAuthentication no

Why this linux distribution can't just use the regular /etc/ssh/sshd_config for its defaults is unclear to me but changing this extra file worked.

Blazonry