Locking Down Remote Access to Linux

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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

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.
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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