How to install Telnet on CentOS/RHEL Linux 6 & 7

What is Telnet?

Telnet is a protocol used to log in to computers remotely over a TCP/IP network. Once a connection is established with the remote computer, it becomes a virtual terminal and allows you to communicate with the remote computer. In this article, we will show you how to install Telnet and how to access remote systems through Telnet.

Install

Open a terminal and enter the following command to install telnet:

yum install telnet telnet-server -y

Now telnet has been installed on your server. Next edit the file /etc/xinetd.d/telnet:

vi /etc/xinetd.d/telnet

Set disable = no:

# 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
}

Save and exit the file. Remember we don’t have to do this step on CentOS 7.

Next use the following command to restart the telnet service:
In CentOS 6.x systems:

service xinetd start

Let this service start every time you restart:

On CentOS 6:

chkconfig telnet on
chkconfig xinetd on

On CentOS 7:

systemctl start telnet.socket
systemctl enable telnet.socket

Let telnet's default port 23 pass through firewalls and routers. To allow the telnet port to pass through the firewall, edit the following file in the CentOS 6.x system:

vi /etc/sysconfig/iptables

Add the following line "-A INPUT -p tcp -m state --state NEW --dport 23 -j ACCEPT":

# 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

Save and exit the file. Restart iptables service:

service iptables restart

In CentOS 7, run the following command to allow the telnet service to pass the firewall.

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

That's it. Now the telnet service can be used.

Create user

Create a test user, for example, the username is "sk" and the password is "centos":

useradd sk
passwd sk

Client configuration

Install telnet package:

yum install telnet

In DEB based systems:

sudo apt-get install telnet

Now, open a terminal and try to access your server (remote host).
If your client is a Linux system, open a terminal and enter the following command to connect to the telnet server.

telnet 192.168.1.150

Enter the username and password created on the server:
Example 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: 
[sk@server1 ~]$

As you can see, the remote host has been successfully accessed locally.
If your system is Windows, go to Start -> Run -> Command Prompt.
In the command prompt, enter the command:

telnet 192.168.1.150

192.168.1.150 is the remote host IP address.
Now you can connect to your server. That's it.

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