ssh连接很慢的解决办法

Posted 2020-10-29

现象：

能ping通目标机器，并且延时是微秒级。

用ssh连其他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。

调试信息：

[email protected]/6 #  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。

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。

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。