Linux - How to install Telnet on Red Hat/OEL ?

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1 - About

Telnet is a service in xinetd.d.

2 - How to install the Telnet Server?

In the installation CD, in the Server directory.

[root@ebs121 Server]# dir | grep -i telnet
perl-Net-Telnet-3.03-5.noarch.rpm
telnet-0.17-39.el5.i386.rpm
telnet-server-0.17-39.el5.i386.rpm
[root@ebs121 Server]# rpm -Uvh telnet-server*
Preparing...                ########################################### [100%]
   1:telnet-server          ########################################### [100%]
[root@ebs121 Server]#
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3 - How to start the Telnet Server?

You can use chkconfig if you want to instead of service. To use chkconfig, the command is

[root@ebs121 Server]# chkconfig telnet on

Alternatively, edit the telnet configuration file (/etc/xinetd.d/telnet) and change disable = yes to disable = no.

If xinetd is not currently running

[root@ebs121 Server]# ps -elf | grep xinetd
5 S root      3325     1  0  77   0 -   680 -      20:49 ?        00:00:00 xinetd -stayalive -pidfile /var/run/xinetd.pid
0 S root      5506  4431  0  78   0 -   979 pipe_w 21:47 pts/1    00:00:00 grep xinetd

The running xinetd (extend Internet service daemon) listens to telnet client request on port 23 and spawn the telnet-server (/usr/sbin/in.telnetd) upon request, shut it down when telnet client drop the connection.

To confirm xinetd is listening to port 23, execute the netstat utility:

[root@ebs121 Server]# netstat -tulpan | grep 23
tcp        0      0 0.0.0.0:723                 0.0.0.0:*                   LISTEN      2661/rpc.statd
tcp        0      0 0.0.0.0:23                  0.0.0.0:*                   LISTEN      3325/xinetd

4 - Root Connection impossible

Telnet client transmit account password in plain text format over (vulnerable) network. Thus, by default, Red Hat Linux (and most Linux distributions) disables telnet daemon and disallow root user to login directly via telnet protocol.

With telnet
Enterprise Linux Enterprise Linux Server release 5.3 (Carthage)
Kernel 2.6.18-128.el5 on an i686
login: gerardnico
Password:password
Last login: Wed Oct 14 12:03:40 on :0
[gerardnico@ebs121 ~]$

5 - Help

[root@ebs121 Server]# man in.telnetd login

6 - Documentation / Reference

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os/linux/telnet.txt · Last modified: 2018/09/16 12:42 by gerardnico