我怎样才能让 sshd 告诉我为什么它的公钥认证失败？

Question

我使用 OpenSSH 6.9p1（在 Lubuntu 上）作为我的 SSH 服务器。当尝试连接到它时（在 Cygwin 中使用 SSH 客户端），尽管我正确生成了我的密钥，将它们放在服务器上的授权密钥文件中，检查权限等，但我仍然被恢复为密码身份验证。

所以，我看看/var/log/auth.log服务器说了什么。我发现这个：

Nov  1 09:50:10 er-thinkpad sshd[16148]: Accepted password for joeuser from 192.168.2.6 port 53325 ssh2
Nov  1 09:50:10 er-thinkpad sshd[16148]: pam_unix(sshd:session): session opened for user joeuser by (uid=0)
Nov  1 09:50:10 er-thinkpad systemd-logind[590]: New session 497 of user joeuser.

...在第一行之前没有关于公钥认证失败的内容。好的，让我们增加详细程度吧。所以我LogLevel从INFO改为VERBOSE并再试一次。现在我得到：

Nov  1 09:53:12 er-thinkpad sshd[16269]: Connection from 192.168.2.6 port 53349 on 192.168.2.2 port 22
Nov  1 09:53:12 er-thinkpad sshd[16269]: Failed publickey for joeuser from 192.168.2.6 port 53349 ssh2: RSA SHA256:removedthis
Nov  1 09:53:12 er-thinkpad sshd[16269]: Failed publickey for joeuser from 192.168.2.6 port 53349 ssh2: ECDSA SHA256:removedthis
Nov  1 09:53:15 er-thinkpad sshd[16269]: Accepted password for joeuser from 192.168.2.6 port 53349 ssh2
Nov  1 09:53:15 er-thinkpad sshd[16269]: pam_unix(sshd:session): session opened for user joeuser by (uid=0)
Nov  1 09:53:15 er-thinkpad systemd-logind[590]: New session 499 of user joeuser.
Nov  1 09:53:15 er-thinkpad sshd[16269]: User child is on pid 16271
Nov  1 09:53:15 er-thinkpad sshd[16271]: Starting session: shell on pts/5 for joeuser from 192.168.2.6 port 53349

太好了，它失败了，但为什么会失败？我怎样才能让 sshd 告诉我呢？

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PS - 只是让你知道，这是客户看到的：

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/joeuser/.ssh/id_rsa
debug1: Authentications that can continue: publickey,password
debug1: Skipping ssh-dss key /home/joeuser/.ssh/id_dsa for not in PubkeyAcceptedKeyTypes
debug1: Offering ECDSA public key: /home/joeuser/.ssh/id_ecdsa
debug1: Authentications that can continue: publickey,password
debug1: Trying private key: /home/joeuser/.ssh/id_ed25519
debug1: Next authentication method: password

Answer 1

在服务器端，将日志级别设置为DEBUG3. 在客户端，使用-vvv选项连接（它也为您DEBUG3提供客户端）。