HOW TO CONFIGURE TELNET SERVER AND TELNET CLIENT IN RHEL/CENTOS/FEDORA
HOW TO CONFIGURE TELNET SERVER AND TELNET CLIENT IN LINUX
Introduction
In this article we are going to discuss on How to configure Telnet Server and Telnet Client in RHEL/CentOS/Fedora. Telnet is nothing but a protocol was invented in 1969 used to take remote of systems over Network in text mode or command mode as it is not supports GUI (Graphical User Interface). There are two instances of Telnet i.e. Telnet Server and Telnet Client. So the concept is you can take the remote console of Telnet Server from client using telnet tools like putty or you can use Command prompt if you are using Windows Operating System. The port number of Telnet is 23. Telnet is no doubt a useful tool but has one major disadvantage is the data transfer over network by telnet is in non-encrypted manner i.e. in Plain Text which is Risky in case of Confidential Data.
So Let’s have a look at configuration steps of Telnet Server and also Telnet Client.
WARNING! : CONFIGURING TELNET IS A BAD IDEA AS ITS TRANSFER’S DATA IN PLAIN TEXT FORMAT (UNENCRYPTED FORMAT). TRY TO AVOID TELNET AS MUCH AS POSSIBLE AND USE SSH INSTADE.
My Scenario :
Telnet Server :
IP Address : 192.168.0.105
Telnet Server Configuration :
Follow the below steps to configure the Telnet Server.
Step : 1 Configure the IP Address
Before start the configuration of Telnet Server, configure the NIC (Network Interface Card) and check properly if the system is in network. Here my IP Address is 192.168.0.105. Refer the output below.
[root@localhost ~]# ifconfig eth0 # Check the IP Address
eth0 Link encap:Ethernet HWaddr 00:0C:29:A4:B6:76
inet addr:192.168.0.105 Bcast:192.168.0.255 Mask:255.255.255.0
inet6 addr: fe80::20c:29ff:fea4:b676/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:70763 errors:0 dropped:0 overruns:0 frame:0
TX packets:23211 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:69485595 (66.2 MiB) TX bytes:1590367 (1.5 MiB)
Step : 2 Install Required Packages for Telnet Server
To start the Telnet Server configuration we need to install some packages :
telnet-server.xxx.xxx.xx.rpm
xinetd.xxx.xxx.xx.rpm
You can install above packages by using YUM Package Repository or by rpm packages from Installation media. Here I am installing using YUM Repository. Refer the output below.
[root@localhost ~]# yum -y install telnet-server # Install telnet-server package
Loaded plugins: fastestmirror, refresh-packagekit, security
Setting up Install Process
Loading mirror speeds from cached hostfile
* base: mirror.nbrc.ac.in
* extras: mirrors.vonline.vn
* updates: mirrors.aluhost.com
Resolving Dependencies
--> Running transaction check
---> Package telnet-server.x86_64 1:0.17-48.el6 will be installed
--> Processing Dependency: xinetd for package: 1:telnet-server-0.17-48.el6.x86_64
--> Running transaction check
---> Package xinetd.x86_64 2:2.3.14-40.el6 will be installed
--> Finished Dependency Resolution
Dependencies Resolved
================================================================================
Package Arch Version Repository Size
================================================================================
Installing:
telnet-server x86_64 1:0.17-48.el6 base 37 k
Installing for dependencies:
xinetd x86_64 2:2.3.14-40.el6 base 122 k
Transaction Summary
================================================================================
Install 2 Package(s)
Total download size: 159 k
Installed size: 313 k
Downloading Packages:
(1/2): telnet-server-0.17-48.el6.x86_64.rpm | 37 kB 00:00
(2/2): xinetd-2.3.14-40.el6.x86_64.rpm | 122 kB 00:00
--------------------------------------------------------------------------------
Total 305 kB/s | 159 kB 00:00
Running rpm_check_debug
Running Transaction Test
Transaction Test Succeeded
Running Transaction
Installing : 2:xinetd-2.3.14-40.el6.x86_64 1/2
Installing : 1:telnet-server-0.17-48.el6.x86_64 2/2
Verifying : 1:telnet-server-0.17-48.el6.x86_64 1/2
Verifying : 2:xinetd-2.3.14-40.el6.x86_64 2/2
Installed:
telnet-server.x86_64 1:0.17-48.el6
Dependency Installed:
xinetd.x86_64 2:2.3.14-40.el6
Complete!
As you can see above we have installed all required packages. To confirm the package installation use the below command.
[root@localhost ~]# rpm -qa | grep telnet-server # Confirm telnet-server package installed or not telnet-server-0.17-48.el6.x86_64 [root@localhost ~]# rpm -qa | grep xinetd # Confirm xinetd package installed or not xinetd-2.3.14-40.el6.x86_64
Now let’s check configuration file location of Telnet Server using rpm -ql command as shown below.
[root@localhost ~]# rpm -ql telnet-server # Check Configuration file locations of Telnet-Server
/etc/xinetd.d/telnet
/usr/sbin/in.telnetd
/usr/share/man/man5/issue.net.5.gz
/usr/share/man/man8/in.telnetd.8.gz
/usr/share/man/man8/telnetd.8.gz
Step : 3 Configure the Telnet Server
So as shown on the output above the main configuration file of telnet server is telnet which is located at /etc/xinetd.d/telnet, So let’s go ahead and enable telnet by edit the configuration file.
To enable the Telnet Server just edit the /etc/xinetd.d/telnet file and find for line disable = yes and change it to disable = no. Follow the output below, Configuration line is highlighted in Red color.
[root@localhost ~]# nano /etc/xinetd.d/telnet # Configuring Telnet-Server # 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 }
After configuration just save the file and start the xinetd service to start the Telnet Server protocol by using below command.
[root@localhost ~]# service xinetd start Starting xinetd: [ OK ]
Now you can connect to Telnet Server using Telnet client tools like putty or if you are using windows Operating System then can use command prompt to connect to telnet server and take console of the Linux Server using normal users. For example I have a username i.e. elinuxbook. refer the output below.
[root@localhost ~]# cat /etc/passwd | grep elinuxbook elinuxbook:x:500:500:elinuxbook:/home/elinuxbook:/bin/bash
Step : 4 Allow root User Login to Telnet Server (If Required)
So here I can connect to Telnet Server by using Username as elinuxbook and Password as Password of elinuxbook.
Disadvantages and Security issue in Telnet :
WARNING! : It’s highly Recommended that you should not allow root login as there may be chances of misuse. Because telnet transfer data in plain text format. Also redhat recommend that use SSH instade of telnet for security reason. But for learning purpose or on your own R & D lab you can use where security is not a matter of concern. I explained this is just for knowledge & information purpose & not to use in production server.
But if you want to login using root then you have to allow on /etc/securetty file. for that just edit the file and paste the below lines. Configuration part is highlighted in Red color.
[root@localhost ~]# nano /etc/securetty # Allow root user to login telnet-server from Client Side pts/0 pts/1 pts/2 pts/3 pts/4 pts/5 pts/6 pts/7 pts/8 pts/9
So we have done with all required configuration from Server Side. Now restart the xinetd service to take effect the configuration.
[root@localhost ~]# service xinetd restart # Restart the xinetd Service
Stopping xinetd: [ OK ]
Starting xinetd: [ OK ]
Then start the xinetd service on startup using below command so that service will start automatically when you restart the system.
[root@localhost ~]# chkconfig --level 35 xinetd on # Start the xinetd service at Startup
Testing From Telnet Client Side :
You can use telnet server to take console/remote of Linux server in text mode/Command Mode for so many purposes, eg : for configuration. To connect to telnet server use tools like putty or in windows operating system you can use command prompt.
Here I am using command prompt to connect to Telnet Server as i am using Windows Operating System.
Login Telnet Server using normal user eg: elinuxbook. Refer the snapshot below.
Connecting to Telnet Server
Login Telnet Server using root user. Refer the snapshot below.
Note : You will only allowed to login through root if you have added pts in /etc/securetty file, Explained above.
connecting to telnet server
This is how we can configure Telnet Server and Telnet Client in RHEL/CentOS/Fedora.
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