How to Generate CSR for Wildcard SSL Certificate in Linux

In today’s digital age, ensuring the security of your website is paramount. One of the essential elements of web security is the SSL (Secure Sockets Layer) certificate, which establishes a secure and encrypted connection between your server and your user’s browsers. A wildcard SSL certificate takes this security a step further by covering multiple subdomains under a single certificate. In this comprehensive guide, we will walk you through how to generate CSR for a wildcard SSL certificate in Linux, ensuring the utmost security for your online presence. Follow these steps to enhance your website’s security and build user trust.

Understanding Wildcard SSL Certificates

Before diving into the steps for generating a CSR, let’s grasp the concept of wildcard SSL certificates.

What are Wildcard SSL Certificates?

A wildcard certificate secures the primary domain and an unlimited number of subdomains with a single certificate. All variations of subdomains under the main domain are protected, making wildcard certificates a cost-effective and efficient choice for businesses with multiple subdomains.

What is a Certificate Signing Request (CSR)?

Certainly! CSR stands for “Certificate Signing Request.” It is a specific type of request made in the field of computer security and digital certificates.

A Certificate Signing Request (CSR) is a formal request made by an individual or an organization to a Certificate Authority (CA) in order to obtain a digital security certificate. This certificate is used to establish the identity of the requester and secure online communications. The CSR includes information about the entity requesting the certificate, such as their public key and details like the organization’s name, domain name, and location.

When a CSR is generated, the requester’s private key is also created. The private key is used to prove ownership of the public key contained in the CSR and to secure communications encrypted with the certificate. The CA reviews the CSR, verifies the requester’s identity, and if everything checks out, the CA will issue the digital certificate.

This certificate is then used for various purposes, including securing websites with HTTPS encryption, establishing secure email communication, and enabling other forms of encrypted data transmission. The CSR process is a fundamental step in ensuring secure online interactions and validating the authenticity of entities on the internet.

How to Generate CSR for Wildcard SSL Certificate in Linux

You Need to Follow These Steps to Generate CSR for Wildcard SSL Certificate in Linux.

Step 1: Accessing Your Linux Server

To begin the process of generating a CSR for your wildcard SSL certificate, you need to access your Linux server. Connect to your server using SSH (Secure Shell) to execute commands and manage your server securely.

Step 2: OpenSSL Installation

Ensure that OpenSSL is installed on your Linux server. OpenSSL is a widely used open-source tool that provides cryptographic functions, including generating SSL certificates.

Checking OpenSSL Installation

To check if OpenSSL is installed, run the following command:

openssl version

If OpenSSL is not installed, you can install it using the package manager for your Linux distribution. For example, on a Debian-based system, you can use:

sudo apt-get install openssl
How to Generate CSR for Wildcard SSL Certificate in Linux
How to Generate CSR for Wildcard SSL Certificate

Step 3: Generating the CSR

Now that OpenSSL is installed, you can proceed to generate the CSR for your wildcard SSL certificate.

  1. Open a terminal window.
  2. Navigate to the directory where you want to store the certificate files.
  3. Run the following OpenSSL command to generate the CSR:
openssl req -new -newkey rsa:2048 -nodes -keyout yourdomain.key -out yourdomain.csr

Replace “yourdomain” with the main domain name for which you are obtaining the wildcard SSL certificate.


The openssl req command is used to generate a CSR. The -new option tells OpenSSL to create a new CSR. The -newkey rsa:2048 option tells OpenSSL to generate a 2048-bit RSA key. The -nodes option tells OpenSSL to generate a key without a password. The -keyout yourdomain.key option tells OpenSSL to save the key file as yourdomain.key. The -out yourdomain.csr option tells OpenSSL to save the CSR file as yourdomain.csr.

Code example:

openssl req -new -newkey rsa:2048 -nodes -keyout yourdomain.key -out yourdomain.csr

Step 4: Filling in CSR Information

When you run the above command, OpenSSL will prompt you to provide information for the CSR. This includes details such as your country, state, locality, organization, organizational unit, common name (main domain), and email address. Fill in the information accurately.

Step 5: Generating a Wildcard CSR

To generate a wildcard CSR, make sure to include an asterisk (*) before the common name (CN) when filling in the information. This tells the certificate authority that you are requesting a wildcard certificate for all subdomains.

Step 6: Saving the CSR

Once you’ve provided all the required information, OpenSSL will generate the CSR file. The private key will be stored in the “yourdomain.key” file, and the CSR will be saved in the “yourdomain.csr” file.

How to Verify the CSR Before Submitting it to a Certificate Authority

How to Generate CSR for Wildcard SSL Certificate in Linux
How to Generate CSR for Wildcard SSL Certificate in Linux

Before submitting the CSR to a certificate authority (CA) for validation and issuance of the wildcard SSL certificate, it’s a good practice to verify the contents of the CSR.

Step 7: Verifying the CSR

You can use the following command to view the CSR details:

openssl req -text -noout -verify -in yourdomain.csr

Step 8: Submitting the CSR to a Certificate Authority

With the verified CSR in hand, you can now approach a trusted certificate authority to purchase and obtain your wildcard SSL certificate. Most CAs have an online portal where you can paste your CSR and follow their validation process.

Step 9: Installing the Wildcard SSL Certificate

After your certificate request is approved by the certificate authority, they will provide you with the wildcard SSL certificate. Follow their instructions to install the certificate on your Linux server, usually involving copying the certificate files to the appropriate directories and configuring your web server (e.g., Apache or Nginx) to use the certificate.


Congratulations! You’ve successfully generated a CSR for a wildcard SSL certificate in a Linux environment. By following these comprehensive steps on how to generate CSR for a wildcard SSL certificate in Linux, you’ve taken a significant stride toward enhancing your website’s security and establishing trust with your users.

Remember, a wildcard SSL certificate not only secures your main domain but also extends its protection to all subdomains, making it an invaluable tool for businesses with a diverse online presence. Keep your online communications encrypted and your users’ data safe by implementing wildcard SSL certificates on your Linux server.

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