If you are looking for the most useful OpenSSL commands, this page is the best place to start. OpenSSL is one of the most widely used command-line tools for working with SSL certificates, TLS connections, private keys, PKCS12 files, CSRs, and certificate troubleshooting. Whether you need to test a remote server, inspect a certificate, convert file formats, or verify a certificate chain, the OpenSSL command line provides the tools to do it.
This page serves as a hub for the most useful OpenSSL tutorials on Mister PKI. Instead of hunting through separate articles one by one, use the sections below to jump directly to the OpenSSL command or certificate task you need. If you administer web servers, Java applications, Linux systems, or PKI infrastructure, these are the OpenSSL commands you will use the most.
Use this OpenSSL commands guide to quickly find help with certificate inspection, TLS testing, PEM conversion, PKCS12 files, self-signed certificates, password handling, and general SSL troubleshooting.
Table of contents
- Most useful OpenSSL commands
- OpenSSL commands by task
- OpenSSL certificate and TLS tutorials
- Popular OpenSSL use cases
- Why use OpenSSL commands
- Frequently asked questions
The diagram below shows how the most common OpenSSL commands relate to TLS testing, certificate inspection, PKCS12 files, and certificate verification.
Most useful OpenSSL commands
If you only need the most common OpenSSL commands, start here. These are some of the most useful OpenSSL tutorials on the site and cover the commands administrators and engineers use most often.
openssl s_client
openssl s_client commands and examples
Use openssl s_client to test remote TLS services, inspect server certificates, verify certificate chains, test SNI, troubleshoot TLS handshakes, and review supported protocol and cipher behavior.
openssl verify
openssl verify – Verify a certificate and certificate chain
Use openssl verify to validate certificates against a chain and trusted CA set. This is one of the most important OpenSSL commands for certificate troubleshooting.
Convert PEM to other formats
PEM conversion is a common OpenSSL task. This guide helps when you need to convert certificate and key material between PEM and other common formats.
PKCS12 and PFX
These articles cover PKCS12 fundamentals, PFX password handling, and the OpenSSL 3.x -legacy option that is sometimes required for older systems and applications.
Create a self-signed certificate
OpenSSL Self Signed Certificate
Use this tutorial when you need to generate a self-signed certificate for testing, internal services, or lab environments.
Install OpenSSL on Ubuntu
How to Install OpenSSL on Ubuntu
If you are just getting started or are setting up a new server, this article shows how to install OpenSSL on Ubuntu and begin using OpenSSL commands on Linux.
OpenSSL commands by task
Sometimes it is easier to think in terms of what you are trying to accomplish rather than by command name. Use the list below to find the right OpenSSL command by task.
- Test a remote TLS server: openssl s_client
- Verify a certificate chain: openssl verify
- Convert PEM files: Convert PEM to other formats
- Create a self-signed certificate: OpenSSL Self Signed Certificate
- Work with PKCS12 or PFX files: pkcs12 and pfx password
- Handle older PKCS12 compatibility issues: openssl pkcs12 legacy
- Install OpenSSL on Linux: How to Install OpenSSL on Ubuntu
OpenSSL certificate and TLS tutorials
OpenSSL is especially useful for SSL certificate and TLS troubleshooting. If your focus is certificates, keys, chain validation, TLS testing, or keystore conversion, these are the best places to begin.
TLS and server testing
PKCS12 and keystores
Popular OpenSSL use cases
Here are some of the most common reasons people search for OpenSSL commands:
- Check whether a server is presenting the correct certificate
- Verify that a certificate chain is complete and trusted
- Convert PEM, CRT, CER, PFX, and PKCS12 files
- Create a self-signed certificate for a lab or internal service
- Inspect a remote TLS service with
openssl s_client - Resolve certificate compatibility issues in older systems
- Install and begin using OpenSSL on Linux
If that sounds like what you are trying to do, the linked tutorials above will cover the commands in much more depth.
Why use OpenSSL commands?
OpenSSL commands remain valuable because they are flexible, scriptable, and available on many Linux and Unix-like systems. For administrators, engineers, and PKI teams, OpenSSL is often the fastest way to inspect certificates, test TLS endpoints, and troubleshoot problems without needing a GUI tool.
They are especially useful when you need repeatable command-line workflows for automation, servers, or troubleshooting in restricted environments.
Official OpenSSL documentation
If you want the vendor documentation, the official OpenSSL command documentation is here:
The official documentation is useful for reference, while the Mister PKI articles above are intended to give practical examples and task-based explanations.
Frequently asked questions
What are the most useful OpenSSL commands?
Some of the most useful OpenSSL commands are openssl s_client, openssl verify, PKCS12-related commands, and commands used to convert PEM files or create self-signed certificates.
What is OpenSSL used for?
OpenSSL is used for working with SSL certificates, private keys, CSRs, PKCS12 files, TLS testing, certificate verification, encryption, and certificate troubleshooting.
How do I inspect a server certificate with OpenSSL?
The most common way is to use openssl s_client, which connects to a remote server and prints certificate and TLS details.
How do I verify a certificate chain with OpenSSL?
Use openssl verify to validate a certificate and its issuing chain against trusted CA certificates.
Can OpenSSL convert certificate files?
Yes. OpenSSL is often used to convert certificate and key material between PEM, CRT, CER, and PKCS12-related formats. See Convert PEM to other formats.
Conclusion
If you need a practical starting point for OpenSSL commands, bookmark this page. It is designed to help you quickly find the right OpenSSL tutorial for certificate inspection, TLS testing, PKCS12 files, PEM conversion, and SSL troubleshooting. As you expand your OpenSSL content on Mister PKI, this hub can also grow with new commands, tutorials, and troubleshooting guides.
For more OpenSSL content, you can also browse the OpenSSL archive.