Shulou(Shulou.com)06/02 Report--

How to install and configure telnet services on Linux and the use of SecureCRT, I believe that many inexperienced people do not know what to do, so this paper summarizes the causes of the problem and solutions, through this article I hope you can solve this problem.

Previously, a virtual machine was installed on the computer, and Linux was installed in the virtual machine, but because there is no way to directly copy the contents of the screen, it is sometimes inconvenient to make notes. So today I installed a SecureCRT on my computer and installed the telnet service on Linux to connect to the Linux in the virtual machine, which makes it easier to copy and paste the screen content. Here's a summary of the steps (I thought a command like yum install telnet-server-y would almost solve it, but I found out I was wrong.

0. Installation of SecureCRT and other preparatory work:

Baidu directly search SecureCRT installation and other keywords, you can find the relevant tutorials, here mainly summarizes the telnet service installation and related configuration, so I will not repeat. In addition, if the installation software uses the yum source (for redhat and centos), the yum-related configuration can refer to the following two articles (Redhat6.4 configuration using local yum source for telnet installation and Redhat6.4 configuration using Centos's yum source for telnet installation):

Https://blog.csdn.net/Apollon_krj/article/details/79831872https://blog.csdn.net/Apollon_krj/article/details/79895546

1. Check the telnet package of the yum source and check the local telnet installation:

Command: yum list | grep telnet

You can see that the yum source has two installation packages, telnet.i686 (client) and telnet-server.i686 (server), @ base indicates that it is installed locally, and base is not installed. So we install the telnet-server.i686 server program.

2. Install telnet-server.i686:

Command: yum install telnet-server.i686-y

3. Check the installation again:

See that the telnet server has been installed.

4. Modify the configuration file to make the xinetd service and telnet service boot:

The configuration files are: / etc/xinetd.d/rsync file and / etc/xinetd.d/telnet file, modified to change the configuration file's disable = yes to disable = no.

Note: telnet service is towed to the xinetd super daemon, that is, it is generally dormant. Xinetd detects that the port it listens to has a client request and then notifies the corresponding service program (but not all services are suitable for hosting xinetd, such as httpd and other frequently accessed service features).

5. Modify the configuration file of pam.d:

Plug-in authentication module: PAM, an authentication mechanism for access control management. Telnet is such an application that uses the PAM module to authenticate logins. A brief understanding of the PAM mechanism can be found in the following picture (picture from the Internet):

Because the telnet connection itself is not secure, root users do not allow telnet connections by default, so we need to modify the relevant configuration files so that we can use root users to connect remotely. Edit the / etc/pam.d/login file of Redhat6.4 and comment out the line "account required pam_nologin.so".

And because the file "/ etc/securetty" saves the terminal name or telnet login that root users can safely log in. If you want root users to log in only from tty1 and tty2, modify the file / etc/securetty, leaving only two lines tty1 and tty2. If you don't want to restrict the login terminal (SecureCRT telnet) type, delete the file. We need to use SecureCRT to connect with telnet, so we need to delete the file (just change the file name).

7. Modify the firewall configuration:

If you start the xinetd service and telnet, but the telnet connection displays deny connection (The remote system refused the connection.) check to see if there is a port disable problem, such as firewall port disabled, manually add allow port 23, save the configuration, and restart the service:

The command is (or check the relevant configuration of the service port in the / etc/services file):

/ sbin/iptables-I INPUT-p tcp-- dport 23-j ACCEPT

/ sbin/iptables-I OUTPUT-p tcp-- dport 23-j ACCEPT

/ etc/init.d/iptables save

Service iptables restart

Service xinetd restart

Modify the firewall configuration and restart the firewall:

Restart the xinetd daemon:

After the restart, both xinetd and telnet will start automatically, eliminating the need to start manually. In fact, using telnet to connect to Linux on SecureCRT is extremely insecure, so using ssh to connect remotely is a more ideal choice, but at present, ssh is not as widely used as telnet. The connection is as follows:

The following figure shows the most common applications of telnet (test environment built with GNS3, SecureCRT, VMWare and WindowsXP virtual machines. For configuration of this environment, please refer to https://blog.csdn.net/Apollon_krj/article/details/81750269 [GNS3 and VMWARE build experimental environment and configure static routing]). Other devices can be accessed on one device through telnet. It is much more convenient to switch between any device that has a smooth network and supports telnet services without having to run back and forth between devices:

After reading the above, do you know how to install and configure telnet services and the use of SecureCRT on Linux? If you want to learn more skills or want to know more about it, you are welcome to follow the industry information channel, thank you for reading!

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.