SSH登录提示Permission denied (publickey)问题求助

问题场景 #

执行ssh root@mail登录远程主机时，返回错误：

root@mail: Permission denied (publickey)

本地与远程主机的~/.ssh目录均存在id_rsa和id_rsa.pub文件，其中私钥id_rsa两端一致，但公钥id_rsa.pub内容不匹配，导致认证失败。debug日志如下：

OpenSSH_8.9p1 Ubuntu-3ubuntu0.5, OpenSSL 3.0.2 15 Mar 2022
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 mail [100.73.xx.yy] port 22.
debug1: Connection established.
debug1: identity file /root/.ssh/id_rsa type 0
debug1: identity file /root/.ssh/id_rsa-cert type -1
debug1: identity file /root/.ssh/id_ecdsa type -1
debug1: identity file /root/.ssh/id_ecdsa-cert type -1
debug1: identity file /root/.ssh/id_ecdsa_sk type -1
debug1: identity file /root/.ssh/id_ecdsa_sk-cert type -1
debug1: identity file /root/.ssh/id_ed25519 type -1
debug1: identity file /root/.ssh/id_ed25519-cert type -1
debug1: identity file /root/.ssh/id_ed25519_sk type -1
debug1: identity file /root/.ssh/id_ed25519_sk-cert type -1
debug1: identity file /root/.ssh/id_xmss type -1
debug1: identity file /root/.ssh/id_xmss-cert type -1
debug1: identity file /root/.ssh/id_dsa type -1
debug1: identity file /root/.ssh/id_dsa-cert type -1
debug1: Local version string SSH-2.0-OpenSSH_8.9p1 Ubuntu-3ubuntu0.5
debug1: Remote protocol version 2.0, remote software version OpenSSH_8.9p1 Ubuntu-3ubuntu0.6
debug1: compat_banner: match: OpenSSH_8.9p1 Ubuntu-3ubuntu0.6 pat OpenSSH* compat 0x04000000
debug1: Authenticating to mail:22 as 'root'
debug1: load_hostkeys: fopen /root/.ssh/known_hosts2: No such file or directory
debug1: load_hostkeys: fopen /etc/ssh/ssh_known_hosts: No such file or directory
debug1: load_hostkeys: fopen /etc/ssh/ssh_known_hosts2: No such file or directory
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: Server host key: ssh-ed25519 SHA256:xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
debug1: load_hostkeys: fopen /root/.ssh/known_hosts2: No such file or directory
debug1: load_hostkeys: fopen /etc/ssh/ssh_known_hosts: No such file or directory
debug1: load_hostkeys: fopen /etc/ssh/ssh_known_hosts2: No such file or directory
debug1: Host 'mail' is known and matches the ED25519 host key.
debug1: Found key in /root/.ssh/known_hosts:1
debug1: ssh_packet_send2_wrapped: resetting send seqnr 3
debug1: rekey out after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: ssh_packet_read_poll2: resetting read seqnr 3
debug1: SSH2_MSG_NEWKEYS received
debug1: rekey in after 134217728 blocks
debug1: Will attempt key: /root/.ssh/id_rsa RSA SHA256:xxxxxxxxxxxxxxxxxxxxxxx
debug1: Will attempt key: /root/.ssh/id_ecdsa
debug1: Will attempt key: /root/.ssh/id_ecdsa_sk
debug1: Will attempt key: /root/.ssh/id_ed25519
debug1: Will attempt key: /root/.ssh/id_ed25519_sk
debug1: Will attempt key: /root/.ssh/id_xmss
debug1: Will attempt key: /root/.ssh/id_dsa
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: kex_input_ext_info: publickey-hostbound@openssh.com=<0>
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey
debug1: Next authentication method: publickey
   debug1: Next authentication method: publickey
debug1: Offering public key: /root/.ssh/id_rsa RSA SHA256:xxxxxxxxxxxxxxxxxxxxxxxx
debug1: Authentications that can continue: publickey
debug1: Trying private key: /root/.ssh/id_ecdsa
debug1: Trying private key: /root/.ssh/id_ecdsa_sk
debug1: Trying private key: /root/.ssh/id_ed25519
debug1: Trying private key: /root/.ssh/id_ed25519_sk
debug1: Trying private key: /root/.ssh/id_xmss
debug1: Trying private key: /root/.ssh/id_dsa
debug1: No more authentication methods to try.
root@mail: Permission denied (publickey)

编辑：经确认该问题并非Tailscale专属，已从标题和标签中移除“tailscale”字样。

解决流程 #

1. 同步公钥到远程主机 #

SSH公钥认证依赖本地公钥与远程主机authorized_keys中的公钥匹配，而非远程主机自身的id_rsa.pub。操作如下：

• 查看本地公钥内容：

  cat ~/.ssh/id_rsa.pub
  

• 通过其他方式（如密码登录、控制台登录）进入远程主机，将上述公钥内容追加到~/.ssh/authorized_keys文件末尾：

  echo "本地公钥完整内容" >> ~/.ssh/authorized_keys
  

• 若远程主机的id_rsa.pub是冗余文件，可直接替换为本地公钥：

  echo "本地公钥完整内容" > ~/.ssh/id_rsa.pub
  

2. 修正文件权限 #

SSH对密钥相关文件权限有严格限制，权限过宽会导致认证失败，执行以下命令修正：

• 设置~/.ssh目录权限为700：

  chmod 700 ~/.ssh
  

• 设置authorized_keys权限为600：

  chmod 600 ~/.ssh/authorized_keys
  

• 设置私钥id_rsa权限为600，公钥id_rsa.pub权限为644：

  chmod 600 ~/.ssh/id_rsa
  chmod 644 ~/.ssh/id_rsa.pub
  

3. 验证登录 #

重新执行ssh root@mail测试登录，若仍失败，可开启debug模式进一步排查：

ssh -v root@mail

内容的提问来源于stack exchange，提问作者Krischu