Difference Between Linux and Unix Explained

Many people use “Unix” and “Linux” as if they were the same thing. They are closely related, and their commands look almost identical, but they have different histories, licences and owners. This guide explains the difference between Linux and Unix in plain terms and shows where each one is used today.

A short history

1969 to 1971: Ken Thompson, Dennis Ritchie and colleagues created Unix at Bell Labs (AT&T).
1970s to 1980s: Unix spread to universities and companies. Berkeley produced BSD, and vendors built their own versions, such as SunOS (later Solaris), HP-UX and IBM AIX.
1983: Richard Stallman started the GNU Project to build a free Unix-like system.
1991: Linus Torvalds released the Linux kernel. Combined with GNU tools, it became a complete, free Unix-like operating system.

So Linux was inspired by Unix and follows its design, but it does not contain original Unix code.

Key differences

Aspect	Unix	Linux
Origin	AT&T Bell Labs, 1969	Linus Torvalds, 1991
What it is	A family of operating systems	A kernel, used in many distributions
Source code	Mostly proprietary (BSD variants are open)	Open source under the GPL
Cost	Usually tied to vendor hardware and licences	Free; optional paid support
Vendors	IBM (AIX), HPE (HP-UX), Oracle (Solaris), Apple (macOS)	Community plus Red Hat, Canonical, SUSE and others
Hardware	Often specific vendor hardware	Almost any hardware, from phones to supercomputers
Certification	“UNIX” is a trademark; systems must pass The Open Group’s certification	Generally not certified as UNIX, though largely POSIX-compatible

What makes a system “Unix”?

Today, UNIX is a registered trademark owned by The Open Group. Only systems that pass its Single UNIX Specification tests may use the name. For example, IBM AIX and Apple macOS are certified. Linux distributions follow most of the same standards, especially POSIX, so they behave like Unix. That is why people call Linux “Unix-like”.

What they have in common

A hierarchical file system starting at /.
“Everything is a file”, including devices.
Multi-user and multitasking design.
Small tools combined with pipes, such as grep, sort and awk.
Shells like sh, Bash and Korn shell.
Similar permissions: owner, group and others.

As a result, skills transfer easily. If you know Linux, you can work on AIX or macOS terminals with little extra learning.

Where each is used today

Unix still runs in long-lived enterprise systems, such as banking, telecom and ERP platforms on IBM Power servers with AIX. Apple’s macOS, a certified UNIX, runs on millions of laptops. The BSD family, including FreeBSD and OpenBSD, powers network appliances and some well-known services.

Linux dominates almost everywhere else: web servers, cloud platforms, containers, supercomputers, Android phones, routers, smart TVs and cars.

Which should you learn?

Learn Linux first. It is free, widely used and the foundation for DevOps, cloud and security careers. Then, if you join an organization that runs AIX or Solaris, your Linux knowledge will carry over.

Related guides

Sources

The Open Group: UNIX standards (unix.org)

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