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Locking Down Remote Access to Linux

In this lab, we will look at how to lock down remote access to a Linux host. We will accomplish this by restricting all remote logins for the `root` account as well as restricting SSH access based on account names.

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Lab Info
Level
Beginner
Last updated
Aug 15, 2025
Duration
30m

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Table of Contents
  1. Challenge

    Prevent remote logins from using the `root` account.
    1. In order to prevent remote logins from using the root account, we'll need to edit the /etc/passwd file. Run the following command:

      sudo vipw 
      
      • select #2 for nano (easiest)
    2. Next, edit the line that starts with root and replace /bin/bash with /sbin/nologin.

    3. Save and exit the /etc/passwd file.

  2. Challenge

    Permit only the `cloud_user` account to connect to the host via SSH.
    1. In order to filter SSH access and only permit the cloud_user account to access the host via SSH, we'll need to edit the sshd_config file with the following command:

      sudo nano /etc/ssh/sshd_config
      
    2. Add the following line to the file just under the second line of the file:

      AllowUsers cloud_user
      

      Note: You can also restrict user access by source hostname, IP address, or subnet, like:

      AllowUsers [email protected]/24
      AllowUsers [email protected]
      AllowUsers [email protected]
      
    3. Now, restart the ssh service with the following command:

      sudo service ssh restart
      
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