失败原因：

1.telnet包未安装，检查telnet包是否安装：  

[root@vm-rhel root]# rpm -qa telnet telnet-0.17-25

 表示已安装

 2.telnet包已安装，telnet-server未安装，检查telnet-server包是否安装： 

[root@vm-rhel root]# rpm -qa telnet-server telnet-server-0.17-25

 表示已安装

 3.telnet配置文件问题：

[root@vm-rhel root]# cat /etc/xinetd.d/telnet# default: on# description: The telnet server serves telnet sessions; it uses \#    unencrypted username/password pairs for authentication.service telnet{    flags        = REUSE    socket_type    = stream            wait        = no    user        = root server = /usr/sbin/in.telnetd log_on_failure += USERID disable = yes }

将disable对应的值修改为no或者注释该行并重启xinetd守护进程：service xinetd restart。

4.Linux防火墙原因，查看防火墙状态：

[root@vm-rhel root]# service iptables status

Table: filter

Chain INPUT (policy ACCEPT)

target prot opt source destination 

RH-Lokkit-0-50-INPUT all -- anywhere anywhere

Chain FORWARD (policy ACCEPT)

target prot opt source destination 

RH-Lokkit-0-50-INPUT all -- anywhere anywhere

Chain OUTPUT (policy ACCEPT)

target prot opt source destination

Chain RH-Lokkit-0-50-INPUT (2 references)

target prot opt source destination 

ACCEPT udp -- 192.168.1.1 anywhere udp spt:domain dpts:1025:65535 

ACCEPT tcp -- anywhere anywhere tcp dpt:smtp flags:SYN,RST,ACK/SYN 

ACCEPT tcp -- anywhere anywhere tcp dpt:http flags:SYN,RST,ACK/SYN 

ACCEPT tcp -- anywhere anywhere tcp dpt:ftp flags:SYN,RST,ACK/SYN 

ACCEPT tcp -- anywhere anywhere tcp dpt:ssh flags:SYN,RST,ACK/SYN 

ACCEPT tcp -- anywhere anywhere tcp dpt:telnet flags:SYN,RST,ACK/SYN 

ACCEPT udp -- anywhere anywhere udp spts:bootps:bootpc dpts:bootps:bootpc 

ACCEPT udp -- anywhere anywhere udp spts:bootps:bootpc dpts:bootps:bootpc 

ACCEPT all -- anywhere anywhere 

ACCEPT all -- anywhere anywhere 

REJECT tcp -- anywhere anywhere tcp dpts:0:1023 flags:SYN,RST,ACK/SYN reject-with icmp-port-unreachable 

REJECT tcp -- anywhere anywhere tcp dpt:nfs flags:SYN,RST,ACK/SYN reject-with icmp-port-unreachable 

REJECT udp -- anywhere anywhere udp dpts:0:1023 reject-with icmp-port-unreachable 

REJECT udp -- anywhere anywhere udp dpt:nfs reject-with icmp-port-unreachable 

REJECT tcp -- anywhere anywhere tcp dpts:x11:6009 flags:SYN,RST,ACK/SYN reject-with icmp-port-unreachable 

REJECT tcp -- anywhere anywhere tcp dpt:xfs flags:SYN,RST,ACK/SYN reject-with icmp-port-unreachable

表示未关闭,如果防火墙已关闭，则不需要在/etc/sysconfig/iptables配置文件中添加：-A RH-Lokkit-0-50-INPUT -p tcp -m tcp --dport 23 --syn -j ACCEPT。

关闭防火墙：service iptables stop (重启后失效：防火墙开机自动启动)

启动防火墙：service iptables start

重启防火墙：service iptables restart

禁止防火墙开机自动启动：chkconfig iptables off

5.默认情况下Linux不允许root用户以telnet方式登录Linux主机，若要允许root用户登录可采用以下3中方法：

  （1）修改/etc/pam.d/login配置文件

         RedHat Linux对于远程登录的限制体现在/etc/pam.d/login文件中，把限制内容注释即可。

[root@vm-rhel root]# cat /etc/pam.d/login#%PAM-1.0auth       required    pam_securetty.soauth       required    pam_stack.so service=system-auth#auth       required    pam_nologin.soaccount    required    pam_stack.so service=system-authpassword   required    pam_stack.so service=system-authsession    required    pam_stack.so service=system-auth session optional pam_console.so

  （2）移除/etc/securetty文件夹

          验证规则设置在/etc/securetty文件中，该文件定义了root用户只能在tty1-tty6的终端上记录，删除该文件或将其改名即可避开验证规则从而实现root用户以telnet方式远程登录Linux主机。

[root@vm-rhel root]# mv /etc/securetty /etc/securetty.bak

  （3）先用普通用户登录，然后切换到root用户

[bboss@vm-rhel bboss]$ su rootPassword: [root@vm-rhel bboss]#