Deal with the too many authentication failures error when initiating SSH connection.
This is related to the MaxAuthTries OpenSSH server option which defines the maximum number of authentication attempts permitted per connection.
By default there are 6 authentication attempts permitted. This is a sane value, so I would vote against increasing or decreasing it, and focus solely on the client configuration.
Too many authentication failures error from the client side.
$ ssh 10.10.1.14
Received disconnect from 10.10.1.14 port 22:2: Too many authentication failures Disconnected from 10.10.1.14 port 22
Too many authentication failures error from the server side.
$ sudo tail -f /var/log/auth.log
[...] Sep 29 22:40:44 debian sshd[727]: error: maximum authentication attempts exceeded for milosz from 10.10.10.254 port 37552 ssh2 [preauth] Sep 29 22:40:44 debian sshd[727]: Disconnecting authenticating user milosz 10.10.10.254 port 37552: Too many authentication failures [preauth] [...]
Sample debug output that clearly indicates that the client tries too many keys.
$ ssh -v 10.10.1.14
OpenSSH_8.4p1 Ubuntu-5ubuntu1.1, OpenSSL 1.1.1j 16 Feb 2021 debug1: Reading configuration data /home/milosz/.ssh/config debug1: Reading configuration data /etc/ssh/ssh_config debug1: /etc/ssh/ssh_config line 19: include /etc/ssh/ssh_config.d/*.conf matched no files debug1: /etc/ssh/ssh_config line 21: Applying options for * debug1: Connecting to 10.10.1.14 [10.10.1.14] port 22. debug1: Connection established. debug1: identity file /home/milosz/.ssh/milosz type 0 debug1: identity file /home/milosz/.ssh/milosz-cert type -1 debug1: Local version string SSH-2.0-OpenSSH_8.4p1 Ubuntu-5ubuntu1.1 debug1: Remote protocol version 2.0, remote software version OpenSSH_8.4p1 Debian-5 debug1: match: OpenSSH_8.4p1 Debian-5 pat OpenSSH* compat 0x04000000 debug1: Authenticating to 10.10.1.14:22 as 'milosz' debug1: SSH2_MSG_KEXINIT sent debug1: SSH2_MSG_KEXINIT received debug1: kex: algorithm: curve25519-sha256 debug1: kex: host key algorithm: ecdsa-sha2-nistp256 debug1: kex: server->client cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none debug1: kex: client->server cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none debug1: expecting SSH2_MSG_KEX_ECDH_REPLY debug1: Server host key: ecdsa-sha2-nistp256 SHA256:FGh6ztmZt2EDte4gOCs7gmso2wSd/wcgOmXpTCtPDlA debug1: Host '10.10.1.14' is known and matches the ECDSA host key. debug1: Found key in /home/milosz/.ssh/known_hosts:185 debug1: rekey out after 134217728 blocks debug1: SSH2_MSG_NEWKEYS sent debug1: expecting SSH2_MSG_NEWKEYS debug1: SSH2_MSG_NEWKEYS received debug1: rekey in after 134217728 blocks debug1: Will attempt key: /home/milosz/.ssh/milosz RSA SHA256:CaC957nx9z3P1vjOuRf8KaVV9enB/aypMYaaCyS5OZE explicit agent debug1: Will attempt key: milosz@milosz-XPS-13-9343 RSA SHA256:W4DzgWYdMqTCKDBG89iNeeyEoqKlexEO3c/TMnWQDLU agent debug1: Will attempt key: milosz@milosz-XPS-13-9343 RSA SHA256:pDpy9cQVs2rY3l2TmQyG+xXjqKWUhYUUhdvNLyu5rWo agent debug1: Will attempt key: milosz@milosz-XPS-13-9343 RSA SHA256:MqT9esnWPypAIAvl/A6AQG7oTx+xbeROJt70vixP+oc agent debug1: Will attempt key: milosz@milosz-XPS-13-9343 RSA SHA256:dEmW5AUt7AEHPLwwsjW+iogUDAF7p0/5tBXILQfqd98 agent debug1: Will attempt key: milosz@desktop RSA SHA256:b4vN4p13EvBznlWSduSMS8iJAZqycrYKkGKvXDDCVdY agent debug1: SSH2_MSG_EXT_INFO received debug1: kex_input_ext_info: server-sig-algs=<ssh-ed25519,sk-ssh-ed25519@openssh.com,ssh-rsa,rsa-sha2-256,rsa-sha2-512,ssh-dss,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384, ecdsa-sha2-nistp521,sk-ecdsa-sha2-nistp256@openssh.com,webauthn-sk-ecdsa-sha2-nistp256@openssh.com> debug1: SSH2_MSG_SERVICE_ACCEPT received debug1: Authentications that can continue: publickey,password debug1: Next authentication method: publickey debug1: Offering public key: /home/milosz/.ssh/milosz RSA SHA256:CaC957nx9z3P1vjOuRf8KaVV9enB/aypMYaaCyS5OZE explicit agent debug1: Authentications that can continue: publickey,password debug1: Offering public key: milosz@milosz-XPS-13-9343 RSA SHA256:W4DzgWYdMqTCKDBG89iNeeyEoqKlexEO3c/TMnWQDLU agent debug1: Authentications that can continue: publickey,password debug1: Offering public key: milosz@milosz-XPS-13-9343 RSA SHA256:pDpy9cQVs2rY3l2TmQyG+xXjqKWUhYUUhdvNLyu5rWo agent debug1: Authentications that can continue: publickey,password debug1: Offering public key: milosz@milosz-XPS-13-9343 RSA SHA256:MqT9esnWPypAIAvl/A6AQG7oTx+xbeROJt70vixP+oc agent debug1: Authentications that can continue: publickey,password debug1: Offering public key: milosz@milosz-XPS-13-9343 RSA SHA256:dEmW5AUt7AEHPLwwsjW+iogUDAF7p0/5tBXILQfqd98 agent debug1: Authentications that can continue: publickey,password debug1: Offering public key: milosz@desktop RSA SHA256:b4vN4p13EvBznlWSduSMS8iJAZqycrYKkGKvXDDCVdY agent Received disconnect from 10.10.1.14 port 22:2: Too many authentication failures Disconnected from 10.10.1.14 port 22
The issue is on the client side, so create a ~/.ssh/config SSH configuration to use specific key.
$ cat ~/.ssh/config
Host 10.10.1.14 PreferredAuthentications publickey PubkeyAuthentication yes IdentitiesOnly yes IdentityFile ~/.ssh/devel
$ ssh -v 10.10.1.14
OpenSSH_8.4p1 Ubuntu-5ubuntu1.1, OpenSSL 1.1.1j 16 Feb 2021 debug1: Reading configuration data /home/milosz/.ssh/config debug1: /home/milosz/.ssh/config line 119: Applying options for 10.10.1.14 debug1: Reading configuration data /etc/ssh/ssh_config debug1: /etc/ssh/ssh_config line 19: include /etc/ssh/ssh_config.d/*.conf matched no files debug1: /etc/ssh/ssh_config line 21: Applying options for * debug1: Connecting to 10.10.1.14 [10.10.1.14] port 22. debug1: Connection established. debug1: identity file /home/milosz/.ssh/devel type 0 debug1: identity file /home/milosz/.ssh/devel-cert type -1 debug1: Local version string SSH-2.0-OpenSSH_8.4p1 Ubuntu-5ubuntu1.1 debug1: Remote protocol version 2.0, remote software version OpenSSH_8.4p1 Debian-5 debug1: match: OpenSSH_8.4p1 Debian-5 pat OpenSSH* compat 0x04000000 debug1: Authenticating to 10.10.1.14:22 as 'milosz' debug1: SSH2_MSG_KEXINIT sent debug1: SSH2_MSG_KEXINIT received debug1: kex: algorithm: curve25519-sha256 debug1: kex: host key algorithm: ecdsa-sha2-nistp256 debug1: kex: server->client cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none debug1: kex: client->server cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none debug1: expecting SSH2_MSG_KEX_ECDH_REPLY debug1: Server host key: ecdsa-sha2-nistp256 SHA256:FGh6ztmZt2EDte4gOCs7gmso2wSd/wcgOmXpTCtPDlA debug1: Host '10.10.1.14' is known and matches the ECDSA host key. debug1: Found key in /home/milosz/.ssh/known_hosts:185 debug1: rekey out after 134217728 blocks debug1: SSH2_MSG_NEWKEYS sent debug1: expecting SSH2_MSG_NEWKEYS debug1: SSH2_MSG_NEWKEYS received debug1: rekey in after 134217728 blocks debug1: Will attempt key: /home/milosz/.ssh/devel RSA SHA256:dAacBlWywkT34TufNIT3stEXSN6GGQL/MieneG2buG8 explicit agent debug1: SSH2_MSG_EXT_INFO received debug1: kex_input_ext_info: server-sig-algs=<ssh-ed25519,sk-ssh-ed25519@openssh.com,ssh-rsa,rsa-sha2-256,rsa-sha2-512,ssh-dss,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384, ecdsa-sha2-nistp521,sk-ecdsa-sha2-nistp256@openssh.com,webauthn-sk-ecdsa-sha2-nistp256@openssh.com> debug1: SSH2_MSG_SERVICE_ACCEPT received debug1: Authentications that can continue: publickey,password debug1: Next authentication method: publickey debug1: Offering public key: /home/milosz/.ssh/devel RSA SHA256:dAacBlWywkT34TufNIT3stEXSN6GGQL/MieneG2buG8 explicit agent debug1: Server accepts key: /home/milosz/.ssh/devel RSA SHA256:dAacBlWywkT34TufNIT3stEXSN6GGQL/MieneG2buG8 explicit agent debug1: Authentication succeeded (publickey). Authenticated to 10.10.1.14 ([10.10.1.14]:22). debug1: channel 0: new [client-session] debug1: Requesting no-more-sessions@openssh.com debug1: Entering interactive session. debug1: client_input_global_request: rtype hostkeys-00@openssh.com want_reply 0 debug1: Remote: /home/milosz/.ssh/authorized_keys:1: key options: agent-forwarding port-forwarding pty user-rc x11-forwarding debug1: Remote: /home/milosz/.ssh/authorized_keys:1: key options: agent-forwarding port-forwarding pty user-rc x11-forwarding debug1: Sending environment. debug1: Sending env LANG = en_US.UTF-8 debug1: Sending env LC_ADDRESS = pl_PL.UTF-8 debug1: Sending env LC_IDENTIFICATION = pl_PL.UTF-8 debug1: Sending env LC_MEASUREMENT = pl_PL.UTF-8 debug1: Sending env LC_MONETARY = pl_PL.UTF-8 debug1: Sending env LC_NAME = pl_PL.UTF-8 debug1: Sending env LC_NUMERIC = pl_PL.UTF-8 debug1: Sending env LC_PAPER = pl_PL.UTF-8 debug1: Sending env LC_TELEPHONE = pl_PL.UTF-8 debug1: Sending env LC_TIME = pl_PL.UTF-8 Linux debian 5.10.0-8-amd64 #1 SMP Debian 5.10.46-5 (2021-09-23) x86_64 The programs included with the Debian GNU/Linux system are free software; the exact distribution terms for each program are described in the individual files in /usr/share/doc/*/copyright. Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent permitted by applicable law. Last login: Wed Sep 29 23:10:13 2021 from 10.10.10.254 milosz@debian:~$