安裝之前瞭解一下Telnet，在公共網路上用telnet傳輸資料不安全，建議只在本地網路上使用

    Using Telnet in public network(WAN) is very very bad idea. It transmits login data in the clear format. Everything will be sent in plain text.
    If you still need Telnet, It is highly recommended use it in the local area network only.
    Alternatively, you can use SSH. But make sure you’ve disabled root login in SSH.

Telnet是通過TCP/IP協議來連線遠端計算機的，一旦建立連線後，它就變成來虛擬終端，由此實現本地和遠端的通訊。

Telnet is a network protocol which is used to connect to remote computers over TCP/IP network. Once you establish a connection to the remote computer, it becomes a virtual terminal and will allow you to communicate with the remote host from your local system.

In this brief tutorial, let us see how to install Telnet, and how to access remote systems via Telnet.
Installation

Open your terminal and type the following command to install telnet:

1，在伺服器上安裝telnet使用：

yum install telnet telnet-server -y

2，編輯telnet的配置檔案

centOS7可以略過這步，本機為centOS6.7

Be mindful that you don’t have do this step in CentOS 7

edit the telnet configuration file /etc/xinetd.d/telnet;

vi /etc/xinetd.d/telnet

把disable設定為no

Set disable = no:

如下

# 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         = no
}

3，Save and quit the file. .

4，重啟telnet服務

Now restart the telnet service using the following command:

On CentOS 6.x systems:

service xinetd start

5，在啟動伺服器時，自動啟動telnet服務，可做如下設定

Make this service to start automatically on every reboot:

On CentOS 6:

chkconfig telnet on
chkconfig xinetd on

On CentOS 7:

systemctl start telnet.socket
systemctl enable telnet.socket

6，讓telnet預設埠通過防火牆，centOS6.x上，編輯iptables

To allow the telnet port through firewall, Edit file /etc/sysconfig/iptables on CentOS 6.x systems:

vi /etc/sysconfig/iptables

新增這句

-A INPUT -p tcp -m state --state NEW --dport 23 -j ACCEPT

如下

# Firewall configuration written by system-config-firewall
# Manual customization of this file is not recommended.
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
-A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
-A INPUT -p icmp -j ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -p tcp -m state --state NEW --dport 23 -j ACCEPT
-A INPUT -m state --state NEW -m tcp -p tcp --dport 22 -j ACCEPT
-A INPUT -j REJECT --reject-with icmp-host-prohibited
-A FORWARD -j REJECT --reject-with icmp-host-prohibited
COMMIT

centOS7，可使用如下命令

On CentOS 7, run the following commands to enable telnet service through firewall.

firewall-cmd --permanent --add-port=23/tcp
firewall-cmd --reload

Save and exit the file.

7，重啟iptables服務

Restart iptables service:

service iptables restart

到這裡，伺服器端telnet就安裝好了

建立測試使用者，使用者名稱 sk， 密碼centos

useradd sk
passwd sk

8，客戶端安裝telnet
安裝 telnet 包:

yum install telnet
在ubnutu上使用如下命令:

sudo apt-get install telnet

9，開啟終端，連線伺服器

Now, open Terminal, and try to access your server(remote host).

telnet 伺服器ip

telnet 192.168.1.150

10，輸入在伺服器上設定的使用者名稱密碼

Enter username and password which we have created in the server:

Sample output:

Trying 192.168.1.150...
Connected to 192.168.1.150.
Escape character is '^]'.
Kernel 3.10.0-123.13.2.el7.x86_64 on an x86_64
server1 login: sk
Password:
[[email protected] ~]$

11，ok. That’s it.

Cheers!

原文地址

http://www.unixmen.com/installing-telnet-centosrhelscientific-linux-6-7/