What is telnet?

Telnet is the networking protocol used to administrate the remote linux or unix system. Telnet is an xined service. We must install the xinetd package and run the xinetd service to use the telnet process. To know more about Xinetd click here.


What are the limitations of telnet?

1. Telnet use plaintext to transmit the password because of this there is no security. Now a days for remote administration we are using ssh only.

2. Root user is not allowed to connect using telnet. To perform the administrative tasks we must do that through SUDO.

3. Telnet is a xinetd service. Xinetd service must be active in order to work on the telnet service.


Working of telnet:

  • Diagram representing the working of the telnet
  • Telnet client or server generally listens at port 23.
  • Whenever the login request is initiated by the client to the telnet server, the server listens the client request at port 23 in TCP.
  • The client will send the login credentials like username and password to the server in plain text mode, because of this only telnet is insecure.
  • Whenever the server received the credentials and authenticates the logins.
  • The connection has established between the client and server the client will send the commands and the server will send the outputs, verbose to the clients etc.,


How to configure the telnet in RHEL?

1. Check whether the telnet package installed or not and also check the xinetd package also.

#rpm –qa telnet-server
#rpm –qa xinetd


[root@sys2 ~]# rpm -qa telnet-server
[root@sys2 ~]# rpm -qa xinetd


The above commands returns nothing so, the packages are not installed.

2. Install the required package for telnet server.

#yum install telnet*
#yum install xinetd*


[root@sys2 ~]# yum install telnet*
Loaded plugins: product-id, refresh-packagekit, security, subscription-manager
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
Setting up Install Process
Package 1:telnet-0.17-47.el6_3.1.x86_64 already installed and latest version
Resolving Dependencies
--> Running transaction check
---> Package telnet-server.x86_64 1:0.17-47.el6_3.1 will be installed
--> Processing Dependency: xinetd for package: 1:telnet-server-0.17-47.el6_3.1.x86_64
--> Running transaction check
---> Package xinetd.x86_64 2:2.3.14-38.el6 will be installed
--> Finished Dependency Resolution Dependencies Resolved
Package              Arch        Version                    Repository         Size
telnet-server       x86_64    1:0.17-47.el6_3.1     ithonors-repo    37 k
Installing for dependencies:
xinetd                  x86_64    2:2.3.14-38.el6         ithonors-repo    121 k
Transaction Summary
Install                2 Package(s)
Total download size: 158 k
Installed size: 313 k
Is this ok [y/N]:y--------------------------Press y to confirm the installation
Downloading Packages:
Total 1.7 MB/s | 158 kB 00:00
Running rpm_check_debug
Running Transaction Test
Transaction Test Succeeded
Running Transaction
Installing : 2:xinetd-2.3.14-38.el6.x86_64 1/2
Installing : 1:telnet-server-0.17-47.el6_3.1.x86_64 2/2
Verifying : 1:telnet-server-0.17-47.el6_3.1.x86_64 1/2
Verifying : 2:xinetd-2.3.14-38.el6.x86_64 2/2 Installed:
telnet-server.x86_64 1:0.17-47.el6_3.1
Dependency Installed:
xinetd.x86_64 2:2.3.14-38.el6


In the above highlited output xinetd is the dependency which is installed during the installation of the telnet server.

3. Check the value in the configuration file of xinetd weather the telnet is enabled or not.

The configuration file for Xinetd is /etc/xinetd.d/telnet. Open the file and set “disable=no”

[root@sys2 ~]# vi /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---------------Set this as no


4. To start the telnet service automatically at boot time the command is

#chkconfig telnet on
[root@sys2 ~]# chkconfig telnet on
[root@sys2 ~]# chkconfig --list telnet
telnet on


Restart the xinetd service.

# /etc/init.d/xinetd restart


5. Create a normal user in order to test the telnet.

>[root@sys2 ~]# useradd alex
[root@sys2 ~]# passwd alex
Changing password for user alex.
New password:
BAD PASSWORD: it is based on a dictionary word
BAD PASSWORD: is too simple
Retype new password:
passwd: all authentication tokens updated successfully.


6. Check the ip address of the server machine.

[root@sys2 ~]# ifconfig –a
eth3 Link encap:Ethernet HWaddr 00:0C:29:F2:03:74
inet addr: Bcast: Mask:
inet6 addr: fdf7:da25:5322:0:20c:29ff:fef2:374/64 Scope:Global
inet6 addr: fe80::20c:29ff:fef2:374/64 Scope:Link
RX packets:4103    errors:0    dropped:0    overruns:0    frame:0
TX packets:582     errors:0    dropped:0    overruns:0    carrier:0                            collisions:0             txqueuelen:1000
RX bytes:386352 (377.2 KiB) TX bytes:80813 (78.9 KiB)


The above highlighted part in the output is the server ipaddress.

7. Turn off the fire walls

[root@sys2 ~]# service iptables stop
iptables: Flushing firewall rules:                            [ OK ]
iptables: Setting chains to policy ACCEPT: filter             [ OK ]
iptables: Unloading modules:                                  [ OK ]
[root@sys2 ~]# /etc/init.d/iptables status
iptables: Firewall is not running.


Client side Configuration:

1. Check the telnet package is installed or not in the client machine if the client is linux.

[root@sys1 ~]# rpm -qa telnet
[root@sys1 ~]# yum install telnet*


2. Now login to the server by using the ip address of server as follows.

[root@sys1 ~]# telnet
telnet: connect to address Connection refused
Connection is refusing. Go to the server and set the selinux to permissive mode and try again.
[root@sys2 ~]# setenforce Permissive
[root@sys2 ~]# getenforce


Now try to login

[root@sys1 ~]# telnet
Connected to
Escape character is '^]'.
Red Hat Enterprise Linux Server release 6.4 (Santiago)
Kernel 2.6.32-358.el6.x86_64 on an x86_64
login: alex
[alex@sys2 ~]$


Now we are successfully logged into the server by using the account of Alex.


If we are using the windows client:

• Simply go to control panel and click turn windows features on or off on programs and features option.




Check the tick on telnet client and click OK

• Now go to cmd and try to access the telnet server.




• Now on the command prompt >telnet




After pressing enter to execute the command you will get the following window to access the remote server.









Compare the above two screen shots and check the files are matched.


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