ssh 连接很慢的解决办法
周海汉 /文
ablozhou # gmail.com
http://blog.csdn.net/ablo_zhou
2009.12.25 圣诞快乐！
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现象：
在局域网内，能ping通目标机器，并且时延是微秒级。
用ssh连局域网内其他linux机器，会等待10-30秒才有提示输入密码。严重影响工作效率。
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客户端操作系统版本：
zhouhh@zhhofs:~$ cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=9.10
DISTRIB_CODENAME=karmic
DISTRIB_DESCRIPTION="Ubuntu 9.10"
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调试信息：
zhouhh@zhhofs:~$ ssh -v 192.168.12.16 OpenSSH_5.1p1 Debian-6ubuntu2, OpenSSL 0.9.8g 19 Oct 2007 debug1: Reading configuration data /etc/ssh/ssh_config debug1: Applying options for * debug1: Connecting to 192.168.12.16 [192.168.12.16] port 22. debug1: Connection established. debug1: identity file /home/zhouhh/.ssh/identity type -1 debug1: identity file /home/zhouhh/.ssh/id_rsa type -1 debug1: identity file /home/zhouhh/.ssh/id_dsa type -1 debug1: Remote protocol version 2.0, remote software version OpenSSH_4.3 debug1: match: OpenSSH_4.3 pat OpenSSH_4* debug1: Enabling compatibility mode for protocol 2.0 debug1: Local version string SSH-2.0-OpenSSH_5.1p1 Debian-6ubuntu2 debug1: SSH2_MSG_KEXINIT sent debug1: SSH2_MSG_KEXINIT received debug1: kex: server->client aes128-cbc hmac-md5 none debug1: kex: client->server aes128-cbc 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 '192.168.12.16' is known and matches the RSA host key. debug1: Found key in /home/zhouhh/.ssh/known_hosts:1 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 debug1: Authentications that can continue: publickey,gssapi-with-mic,password debug1: Next authentication method: gssapi-with-mic debug1: An invalid name was supplied Cannot determine realm for numeric host address debug1: An invalid name was supplied Cannot determine realm for numeric host address debug1: An invalid name was supplied debug1: Next authentication method: publickey debug1: Trying private key: /home/zhouhh/.ssh/identity debug1: Trying private key: /home/zhouhh/.ssh/id_rsa debug1: Trying private key: /home/zhouhh/.ssh/id_dsa debug1: Next authentication method: password [email protected]'s password: debug1: Authentication succeeded (password). debug1: channel 0: new [client-session] debug1: Entering interactive session. debug1: Sending environment. debug1: Sending env LANG = zh_CN.UTF-8 Last login: Fri Dec 25 13:35:04 2009 from 192.168.11.146
可以看到如下的错误信息：
debug1: Next authentication method: gssapi-with-mic
debug1: An invalid name was supplied
Cannot determine realm for numeric host address
事实上，正是从gssapi-with-mic这一行开始，开始耗时间。
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失败的尝试：
有人说是在目标机器中修改/etc/ssh/sshd_conf文件
将UseDNS 的缺省值由yes修改为no，并重启sshd。我试了，对这种情况不管用。但不排除对别的延迟情况管用。
====================
有效的解决办法：
1. 修改本地机器的hosts文件，将目标机器的IP和域名加上去。或者让本机的DNS 服务器能解析目标地址。
vi /etc/hosts
192.168.12.16 ourdev
其格式是“目标机器IP 目标机器名称”这种方法促效。没有延迟就连上了。不过如果给每台都加一个域名解析，挺辛苦的。但在windows下用putty或secure-crt时可以采用这种方法。
2.修改本机的客户端配置文件ssh_conf，注意，不是sshd_conf
vi /etc/ssh/ssh_conf
找到
GSSAPIAuthentication yes
改为
GSSAPIAuthentication no
保存。
再连目标机器，速度就飞快了。
GSSAPI ( Generic Security Services Application Programming Interface) 是一套类似Kerberos 5 的通用网络安全系统接口。该接口是对各种不同的客户端服务器安全机制的封装，以消除安全接口的不同，降低编程难度。但该接口在目标机器无域名解析时会有问题。我看到有人给ubuntu提交了相关bug， 说要将GSSAPIAuthentication的缺省值设为no，不知为何，ubuntu9.10的缺省值还是yes。
修改完毕，此时的连接调试数据变为了：
zhouhh@zhhofs:~$ ssh -v 192.168.12.16 OpenSSH_5.1p1 Debian-6ubuntu2, OpenSSL 0.9.8g 19 Oct 2007 debug1: Reading configuration data /etc/ssh/ssh_config debug1: Applying options for * debug1: Connecting to 192.168.12.16 [192.168.12.16] port 22. debug1: Connection established. debug1: identity file /home/zhouhh/.ssh/identity type -1 debug1: identity file /home/zhouhh/.ssh/id_rsa type -1 debug1: identity file /home/zhouhh/.ssh/id_dsa type -1 debug1: Remote protocol version 2.0, remote software version OpenSSH_4.3 debug1: match: OpenSSH_4.3 pat OpenSSH_4* debug1: Enabling compatibility mode for protocol 2.0 debug1: Local version string SSH-2.0-OpenSSH_5.1p1 Debian-6ubuntu2 debug1: SSH2_MSG_KEXINIT sent debug1: SSH2_MSG_KEXINIT received debug1: kex: server->client aes128-cbc hmac-md5 none debug1: kex: client->server aes128-cbc 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 '192.168.12.16' is known and matches the RSA host key. debug1: Found key in /home/zhouhh/.ssh/known_hosts:1 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 debug1: Authentications that can continue: publickey,gssapi-with-mic,password debug1: Next authentication method: publickey debug1: Trying private key: /home/zhouhh/.ssh/identity debug1: Trying private key: /home/zhouhh/.ssh/id_rsa debug1: Trying private key: /home/zhouhh/.ssh/id_dsa debug1: Next authentication method: password [email protected]'s password: