How to configure remote login (such as SSH and Telnet) on Linux

How to configure remote login (such as SSH and Telnet) on Linux

Remote login is a very convenient way that allows us to connect to a remote server or computer from anywhere for operation and management. In Linux systems, we can achieve remote login by configuring SSH (Secure Shell Protocol) and Telnet. This article will show how to configure remote login on Linux, with code examples.

1. SSH (Secure Shell Protocol) configuration:
SSH is a secure remote login protocol that uses encryption technology to protect remote login communication security.

1. Check if SSH is installed:
   Enter the following command in the terminal to check if SSH is installed on your system:

   $ ssh -V

   If SSH is displayed version information, it means that SSH has been installed. If it is not installed, you can use the following command to install it:

   $ sudo apt-get install openssh-server    # Ubuntu / Debian系统
   $ sudo yum install openssh-server        # CentOS / Red Hat系统

2. Modify the SSH configuration file:
   Use an editor to open the SSH configuration file and enter the following command in the terminal:

   $ sudo vi /etc/ssh/sshd_config

   Find the following line in the configuration file and modify it accordingly:

   PermitRootLogin yes              # 允许root用户远程登录（可选）
   PasswordAuthentication yes      # 允许密码进行身份验证

   After completing the modification, save the file and exit the editor.

3. Restart the SSH service:
   Enter the following command in the terminal to make the SSH configuration changes take effect:

   $ sudo service ssh restart

4. Connect to the remote host :
   In a terminal on another computer, enter the following command to connect to the remote host:

   $ ssh username@remote_host

   where username is your username on the remote host and remote_host is the IP address of the remote host or CPU name.

2. Telnet configuration:
Telnet is an insecure remote login protocol. It transmits the user's input information in plain text and does not have encryption and security.

1. Check if Telnet is installed:
   Enter the following command in the terminal to check if Telnet is installed on your system:

   $ telnet

   If telnet is displayed: command not found means Telnet is not installed. You can use the following command to install:

   $ sudo apt-get install telnet    # Ubuntu / Debian系统
   $ sudo yum install telnet        # CentOS / Red Hat系统

2. Modify the Telnet configuration file:
   Use an editor to open the Telnet configuration file and enter the following command in the terminal:

   $ sudo vi /etc/xinetd.d/telnet

   Find The following lines, and modify them accordingly:

   disable = no     # 将disable的值改为no

   After completing the modifications, save the file and exit the editor.

3. Restart the Telnet service:
   Enter the following command in the terminal to make the Telnet configuration changes take effect:

   $ sudo service xinetd restart

4. Connect to the remote host :
   In a terminal on another computer, enter the following command to connect to the remote host:

   $ telnet remote_host

   Where remote_host is the IP address or hostname of the remote host.

Note: Since Telnet is not secure, it is recommended to only be used within the internal network.

Summary:
This article shows how to configure remote login on a Linux system, including SSH and Telnet. SSH provides an encrypted and secure remote login method, while Telnet is an insecure method. When configuring remote login, you should give priority to SSH to protect the security of remote communication.

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