实例解析：在RHEL 5上telnet的开启过程

1、确定你的telnet服务打开没有：

[root@111 ~]# chkconfig --list|grep telnet

ekrb5-telnet: off

krb5-telnet: off

[root@111 ~]#

注意检查结果这里是关闭状态

2、打开telnet服务：

[root@111 ~]# chkconfig krb5-telnet on

[root@111 ~]# chkconfig --list|grep telnet

ekrb5-telnet: offv

krb5-telnet: on

[root@111 ~]#

检查已经被打开了

3、修改登陆文件securetty,主要增加要登陆的终端点

[root@111 ~]# vi /etc/securetty

增加如下几行：

pts/1

pts/2

pts/3

pts/4

pts/5

……

保存退出即可。

如果是chkconfig krb5-telnet on

会提示Unencrypted connection refused. Goodbye.Connection closed by foreign host.看错误信息好像是说的为加密的连接被拒绝，查看了他的配置文件也没发现有什么关于加密的选项，而且配置文件也很正确，于是到google上去搜索了一大圈，最后终于找到一个老外写的一个解决方法：

I really needed a bit of guidance and you provided it./sbin/chkconfig --list |grep telnetThe above command told me I had both krb5-telnet and ekrb5-telnet, andalso the installed telnet all on. Initially I did not know what theywere all for. After turning them on and off and testing my telnetconnection from another box I realised that "ekrb5-telnet" was theencrypted telnet server that I needed to turn off to run "krb-telnet"which allowed non-encrypted telnet connections.eg /sbin/chkconfig ekrb5-telnet offThanks for your help.
 

原来ekrb5-telnet是一个需要加密的telnet服务，把这个服务启动上当然就需要加密了。解决方法：将/etc/xinetd.d/ekrb5-telnet里面的disable改成=yes，再重启xinetd服务service xinetd restart就OK了！