尝试通过 SSH 连接到系统时出现延迟答案

【问题标题】：Delay when attempting to SSH to a system尝试通过 SSH 连接到系统时出现延迟
【发布时间】：2013-11-21 11:49:59
【问题描述】：

当我尝试从我的系统 ssh 到朋友的系统时，我面临大约 5-6 秒的延迟。这是命令的详细输出：

zeus@athena:~$ ssh -v ashwin@192.168.40.211
OpenSSH_5.3p1 Debian-3ubuntu7, OpenSSL 0.9.8k 25 Mar 2009
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug1: Connecting to 192.168.40.211 [192.168.40.211] port 22.
debug1: Connection established.
debug1: identity file /home/zeus/.ssh/identity type -1
debug1: identity file /home/zeus/.ssh/id_rsa type 1
debug1: Checking blacklist file /usr/share/ssh/blacklist.RSA-2048
debug1: Checking blacklist file /etc/ssh/blacklist.RSA-2048
debug1: identity file /home/zeus/.ssh/id_dsa type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_6.0p1 Debian-3ubuntu1
debug1: match: OpenSSH_6.0p1 Debian-3ubuntu1 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.3p1 Debian-3ubuntu7
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: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<8192) sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
debug1: Host '192.168.40.211' is known and matches the RSA host key.
debug1: Found key in /home/zeus/.ssh/known_hosts:71
debug1: ssh_rsa_verify: signature correct
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received

<---- delay 4-5 seconds------>


debug1: Authentications that can continue: publickey,password
debug1: Next authentication method: publickey
debug1: Trying private key: /home/zeus/.ssh/identity
debug1: Offering public key: /home/zeus/.ssh/id_rsa
debug1: Authentications that can continue: publickey,password
debug1: Trying private key: /home/zeus/.ssh/id_dsa
debug1: Next authentication method: password

有人可以帮我弄清楚如何摆脱这种延迟吗？

【问题讨论】：

一个常见的 DNS 问题。见superuser.com/questions/372238 和sysadvent.blogspot.nl/2010/12/…
这很有帮助。谢谢。

标签： bash ssh openssh

【解决方案1】：

正如 cmets 中所建议的，这可能是 DNS 问题。有一篇文章介绍了尝试解决此问题的一些步骤： http://www.thegeekstuff.com/2010/07/openssh-slow-at-ssh2_msg_service_accept-received/

给出的建议归结为编辑/etc/sshd_config 添加/更改UseDNS no，然后重新启动sshd。显然，如果不访问服务器，这可能会很棘手！

还应该指出，从长远来看，将UseDNS 设置为no 可能不是最佳解决方案。如果有问题的话，最好解决机器上的 DNS 问题。

【讨论】：

【解决方案2】：

我的问题似乎在这里有了答案：

https://superuser.com/a/654153/152271

似乎远程主机试图对我的主机名（连接的主机名）进行 nslookup。在远程主机中编辑 /etc/hosts 添加我的 IP/主机名后，它修复了延迟。

【讨论】：