Do you feel like you’re always missing something security-related when deploying your application?
Creating a public server is an anxious feeling. How do you protect your data and keep the bad guys out?
A Platform-as-a-Service like Heroku charges a premium to handle server security. Wouldn’t it be nice if you had the affordable price of a VPS and the peace of mind of a PaaS?
Learn the 80/20 rule to securing a server and apply these four security measures to stay ahead of your peers.
Use the accompanying guide as a security checklist next time you create a server.
1. Use a non-root user
First thing I usually do to secure a new VPS instance is to create a new user. I use this user instead of
root to log into the VPS and run commands. It’s good to avoid using the
root user because it has unrestricted access to the machine and can potentially cause serious damage.
Using a non-root user follows the principle of least privilege and adds a layer of protection against intruders looking to gain
Note: This is not a comprehensive list of security best practices but rather a few essential measures that will go a long way in hardening a server. Additional security measures include file auditing, isolated execution environments (with Docker), rate-limiting with fail2ban, and more.
Creating a new user
While logged into the VPS as
root, create a new user with the following command:
# Choose any username you want adduser maxim
You’ll be asked to create a password and fill in a few additional questions. Only the password is required and you can hit
enter to leave everything else blank. Remember the password because you will need it every time you use
sudo to get privileged access.
Note: All commands in this article are for Ubuntu. Other Linux distributions usually have equivalent programs that can do the same thing. If you Google
<command> equivalent <distribution> (e.g.:
adduser equivalent fedora) you have a good chance of finding what you’re looking for.
To verify the user has been created successfully, you can run
$ id maxim uid=1000(maxim) gid=1000(maxim) groups=1000(maxim)
Subsequently, we’ll give this user the ability to run commands as
sudo since we will need that later in this article. You can accomplish that by adding the user to the
# Use your username here usermod -aG sudo maxim
-aG stands for append to group. If you run
id <user> again you can see
sudo has been added to this user’s group list.
$ id maxim uid=1000(maxim) gid=1000(maxim) groups=1000(maxim),27(sudo)
Setup SSH for the new user
Next step is to add your public key to the user’s
.ssh folder so you can log in as the user with SSH.
Let’s switch to the new user and create a
.ssh folder in the user’s home directory:
# Switch to the new user su - maxim # Create the SSH folder mkdir ~/.ssh
SSH is nit-picky about files and folders permissions and it will fail with an error if they are too permissive. Let’s change the folder’s permission so only this user is allowed to read and write to it:
# Restrict access to this user only chmod 700 ~/.ssh
In this folder, we’ll create a file named
authorized_keys which will contain your public key. SSH will look for the key in this file when you connect to the server.
# Create and open the file where SSH will look for your public key nano ~/.ssh/authorized_keys
The above command will open the file in the
nano editor allowing you to paste your public key. Hit
CTRL + X to quit, then
enter to save.
A quick way to copy the contents of a file in the terminal is to use
pbcopy. To copy your public key, navigate to the
.ssh folder on your machine and run
pbcopy < id_rsa.pub (assuming
id_rsa.pub is the name of your public key file). The public key is then copied to the clipboard and you can paste it anywhere you want.
Confirm the key is saved by running
cat ~/.ssh/authorized_keys. This will print the contents of the file to the terminal and you should see your public key.
Let’s change the permissions of this file as well:
# Restrict access to this user only chmod 600 ~/.ssh/authorized_keys
Open a second terminal session and confirm you can SSH into the server with
ssh <user>@<server_ip>. If you’ve followed the above steps correctly, you should see the Ubuntu welcome message.
Close the first terminal session by running
exit twice and proceed to the next section.
2. Disable password and root login
Cloud servers are often a target for brute force attacks. Using SSH with a password poses a security threat as passwords tend to be weak and eventually guessable given enough time.
A private/public key pair has many more bits of data making them impossible to guess in within the human lifespan.
It’s good practice to disable password login and protect your VPS from these type of attacks. It also gives you peace of mind that, unless an attacker gets a hold of your private key, the only person who will have access to the server is you.
While we’re at it, we will also disable logging in as
root since we will not be using it anymore.
Both settings are in a global SSH configuration file. Changing this file requires you to use
sudo which will ask you for a password. This is the same password you chose when you created the user.
# Open the SSH config file in the `nano` editor sudo nano /etc/ssh/sshd_config
Scroll down until you find
PermitRootLogin and change its value to
no. Do the same for
PasswordAuthentication. Make sure they’re not commented out by removing any leading
CTRL + X to quit, then
enter to save.
Finally, you need to restart the SSH service for the changes to take effect:
# Restart the SSH service sudo systemctl reload sshd
Verify that root and password login are disabled by trying to log in as the root user
ssh [email protected]<server_ip>. You should see
Permission denied (publickey). printed in the terminal.
3. Block incoming traffic on non-public ports
Using a firewall to close all ports, except those that need to be public, is an essential part of server security. Every application running on a machine is a potential vulnerability that can be exploited by an intruder.
Fewer exposed applications means a smaller attack surface resulting in a more secure server.
A firewall consists of a set of rules. Each rule serves as a filter for incoming/outgoing traffic deciding whether a package is allowed to continue to its destination or not.
We’ll use UFW (Uncomplicated FireWall) to create firewall rules. UFW is an easy-to-use program built on top of
iptables — the traditional and more difficult interface for configuring firewall rules. UFW comes pre-installed on Ubuntu.
For most newly-created VPS instances, we want to begin by opening up three ports: 22 for SSH, 80 for HTTP traffic and 443 for HTTPS traffic. You can open a specific port or you can specify a service name that is mapped to a port. In the examples below we use service names.
sudo ufw allow http is the same as
sudo ufw allow 80/tcp.
# Allow SSH connections sudo ufw allow ssh # Allow HTTP traffic sudo ufw allow http # Allow HTTPS traffic sudo ufw allow https
You will see two rules added after each command, one for IPv4 and another for IPv6. The rules don’t go into effect until we enable the firewall:
# Enable firewall sudo ufw enable
You will get a warning that enabling the firewall might close the active SSH connection. We’ve added a rule for SSH so we don’t have to worry about that. Type
y followed by
enter to proceed.
Let’s verify the firewall is up and running:
$ sudo ufw status Status: active To Action From -- ------ ---- 22/tcp ALLOW Anywhere 80/tcp ALLOW Anywhere 443/tcp ALLOW Anywhere 22/tcp (v6) ALLOW Anywhere (v6) 80/tcp (v6) ALLOW Anywhere (v6) 443/tcp (v6) ALLOW Anywhere (v6)
You might add additional services in the future that need to be open to the public. The syntax for exposing a port is:
sudo ufw allow <port>/tcp. To close a port, you run:
sudo ufw deny <port>/tcp. Changes will take effect immediately without needing to restart the firewall.
4. Enable automatic security updates
The final step to making the server more secure is to enable automatic security updates. The open-source community frequently releases security updates making sure vulnerabilities are patched soon after they are found. Conducting manual updates regularly is time-consuming and often forgotten.
By automating this process you’re making sure the system is up-to-date with the latest security fixes.
Note: Automatic updates are only applied to software installed through the Ubuntu package manager and don’t include application-specific dependencies (e.g.: npm dependencies for Node.js). It’s good practice to update your app’s dependencies from time to time.
Ubuntu comes pre-installed with a package named
unattended-upgrades that lets us configure automatic updates. This tool will regularly check if the packages installed on your machine have new releases and install them if needed. You can granularly specify which updates you want to be installed and which ones to skip. We’ll turn automatic updates only for security releases to minimise the chance of introducing breaking changes.
The following command enables automatic security updates:
# Enable automatic security updates sudo dpkg-reconfigure --priority=low unattended-upgrades
You will see an interactive dialog asking if you want to enable automatic updates, select
This command edits two files:
/etc/apt/apt.conf.d/20auto-upgrades(configures when and how the script should run)
/etc/apt/apt.conf.d/50unattended-upgrades(configures whether an update should be installed or skipped)
If you want to learn more, visit the automatic security updates documentation on the Ubuntu website.
To verify that automatic updates are enabled:
$ apt-config dump APT::Periodic::Unattended-Upgrade APT::Periodic::Unattended-Upgrade "1";
"1" stands for every
1 day. You’ve now enabled daily automatic security updates for your server and won’t have to worry about that anymore. 🎉
Prefer video? Watch it in action!
We’ve implemented 4 quick steps that go a long way in securing a VPS. We:
- Created a non-root user instead of using root to mitigate the security threat
- Prevented brute force attacks by disabling password login
- Blocked incoming traffic on non-public ports thereby reducing the attack surface
- Ensured the system is up-to-date with the latest vulnerability patches by enabling automatic security updates
By applying these measures you’re far ahead of the majority of the cloud servers that are out there in the wild. It’s a low amount of effort in return for peace of mind. Pat yourself for being a good citizen of the cloud. 🌟☁️