前言

为了测试telnet，首先，要保证系统已经安装了telnet，并且还得有一个端口能用,就是1-65536那个PORT。

一搭建telenet环境并测试

1 首先查看telnet运行状态：

lkmao@ubuntu:~$ netstat -a | grep telnet
lkmao@ubuntu:~$

输出为空，表示没有开启该服务

2 安装openbsd-inetd

 sudo apt-get install openbsd-inetd

如果已经安装过了，会提示已经安装过了，直接执行下面的步骤就可以了。

3 安装telnetd

sudo apt-get install telnetd

安装完之后，查看/etc/inetd.conf的内容，我的是第23行

telnet stream tcp nowait telnetd /usr/sbin/tcpd /usr/sbin/in.telnetd

 # /etc/inetd.conf:  see inetd(8) for further informations.
  2 #
  3 # Internet superserver configuration database
  4 #
  5 #
  6 # Lines starting with "#:LABEL:" or "#<off>#" should not
  7 # be changed unless you know what you are doing!
  8 #
  9 # If you want to disable an entry so it isn't touched during
 10 # package updates just comment it out with a single '#' character.
 11 #
 12 # Packages should modify this file by using update-inetd(8)
 13 #
 14 # <service_name> <sock_type> <proto> <flags> <user> <server_path> <args>
 15 #
 16 #:INTERNAL: Internal services
 17 #discard        stream  tcp nowait  root    internal
 18 #discard        dgram   udp wait    root    internal
 19 #daytime        stream  tcp nowait  root    internal
 20 #time       stream  tcp nowait  root    internal
 21 
 22 #:STANDARD: These are standard services.
 23 telnet      stream  tcp nowait  telnetd /usr/sbin/tcpd  /usr/sbin/in.telnetd
 24 
 25 #:BSD: Shell, login, exec and talk are BSD protocols.
 26 
 27 #:MAIL: Mail, news and uucp services.
 28 
 29 #:INFO: Info services
 30 
 31 #:BOOT: TFTP service is provided primarily for booting.  Most sites
 32 #       run this only on machines acting as "boot servers."
 33 
 34 #:RPC: RPC based services
 35 
 36 #:HAM-RADIO: amateur-radio services
 37 
 38 #:OTHER: Other services
 39

使用grep搜索如下所示：

lkmao@ubuntu:~$ cat /etc/inetd.conf  | grep telnet 
telnet          stream  tcp     nowait  telnetd /usr/sbin/tcpd  /usr/sbin/in.telnetd
lkmao@ubuntu:~$

4 重启openbsd-inetd

lkmao@ubuntu:~$ /etc/init.d/openbsd-inetd restart
[....] Restarting openbsd-inetd (via systemctl): openbsd-inetd.service==== AUTHENTICATING FOR org.freedesktop.systemd1.manage-units ===
需要通过认证才能重启“inetd.service”。
Authenticating as: lkmao,,, (lkmao)
Password: 
==== AUTHENTICATION COMPLETE ===
. ok 
lkmao@ubuntu:~$

5 查看telnet运行状态，

如下所示，已经处于监听的状态了。此时表明已经开启了telnet服务。

lkmao@ubuntu:~$ netstat -a | grep telnet
tcp        0      0 *:telnet                *:*                     LISTEN     
lkmao@ubuntu:~$

6 telnet登陆测试

输入telnet 127.0.0.1,如果连接成功，会提示输入用户名，输入密码，就可以成功登录了。

lkmao@ubuntu:~$ telnet 127.0.0.1
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
Ubuntu 16.04.7 LTS
ubuntu login:

完整过程如下所示：

二自动登录telnet的脚本：

#!/usr/bin/expect
spawn telnet 127.0.0.1
expect {
    "login:" {
        send "lkmao\n";exp_continue
    }   
    "assword" {
        send "lkmao\n"
    }   
}
interact

执行效果：