在身份验证可以继续之前 ssh 变慢

Question

我已经在谷歌上搜索这个问题一段时间了，但我还没有找到有效的解决方案。
问题是 SSH 登录到我的服务器突然变得很慢。我可以看到身份验证需要大约 10 秒才能继续，这是我的 ssh 详细日志:

OpenSSH_7.3p1, LibreSSL 2.4.1
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 20: Applying options for *
debug1: Connecting to 54.86.29.78 [54.86.29.78] port 22.
debug1: Connection established.
debug1: key_load_public: No such file or directory
debug1: identity file .ssh/id_rsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file .ssh/id_rsa-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_7.3
debug1: Remote protocol version 2.0, remote software version OpenSSH_6.6.1p1 Ubuntu-2ubuntu2.4
debug1: match: OpenSSH_6.6.1p1 Ubuntu-2ubuntu2.4 pat OpenSSH_6.6.1* compat 0x04000000
debug1: Authenticating to 54.86.29.78:22 as 'perfeyhe'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: algorithm: curve25519-sha256@libssh.org
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:g/REeuiZutP7YHv6WJR/vhm4kROJQ+9e0ODdd1Tuvpc
debug1: Host '54.86.29.78' is known and matches the ECDSA host key.
debug1: Found key in /Users/admin/.ssh/known_hosts:3
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS received
debug1: SSH2_MSG_SERVICE_ACCEPT received
----------------------------------
takes about 10s
----------------------------------
debug1: Authentications that can continue: publickey,password,keyboard-interactive
debug1: Next authentication method: publickey
debug1: Trying private key: .ssh/id_rsa
debug1: Authentication succeeded (publickey).
Authenticated to 54.86.29.78 ([54.86.29.78]:22).
debug1: channel 0: new [client-session]
debug1: Requesting no-more-sessions@openssh.com
debug1: Entering interactive session.
debug1: pledge: network
debug1: Sending environment.
debug1: Sending env LANG = zh_CN.UTF-8
Welcome to Ubuntu 14.04.3 LTS (GNU/Linux 3.13.0-74-generic x86_64)

附件是我从wireshark看到的:
enter image description here

Answer 1

延迟发生在服务器上，因此您在客户端日志和客户端 Wireshark 转储中都看不到任何重要内容。

有几种可能会导致这种情况，但很可能在服务器 UseDNS 中启用了 sshd_config 。尝试禁用它(将 UseDNS no 写入 /etc/ssh/sshd_config )，重新启动 sshd 服务( service sshd restart )并重试。

如果它没有帮助，请在同一文件中设置 DEBUG3 LogLevel，重新启动并查看服务器日志“挂起”的位置以及它在等待什么。