What is Unix?
Author: Domeny.ForSale editorial team Published
In brief: Unix is an operating system developed at Bell Labs whose design became the foundation of an entire family of systems and influenced many others. It was designed to support multiple users and run multiple tasks at the same time. Linux is a Unix-like system, not simply another name for Unix; macOS has Unix foundations, and specific versions and configurations have received UNIX certification.
What is Unix, and where did it come from?
An operating system is software that manages hardware and allows programs to run. It allocates memory and processor time to them, handles files and controls access to resources. This is precisely what Unix does—it is not a programming language or a single application.
Its origins date back to the late 1960s and work at Bell Labs. Ken Thompson and Dennis Ritchie were among its most important creators. Rewriting a substantial part of the system in C made it easier to port to different computers, rather than building each version almost from scratch for specific hardware.
Over time, different variants of Unix emerged. Today, the word “Unix” can therefore refer to the historical system, a family of systems or a set of characteristic principles governing how they work. It should not be treated as the name of a single product that always looks and works identically.
How does a Unix system work?
The central component of the system is the kernel, which manages the processor, memory, devices and processes. A process is a running program together with the resources it needs to operate. Utility tools, services and user interfaces operate around the kernel.
Typical features of Unix systems include:
- Multitasking: many processes can run concurrently, such as a web server, a database and a text editor.
- Multi-user support: many users can use the same system, including through remote connections.
- A hierarchical file system: directories form a single tree starting at
/, the root directory. - Permissions: access to files and directories is controlled, including through permissions for the owner, group and other users.
For example, on a company server, an application account may have permission to write to a directory containing uploaded documents, but not to modify system files. This separation limits the consequences of an error or an application being compromised. Permissions alone do not provide complete security, however—updates and correct configuration are also necessary.
Unix is also associated with the principle of building small tools that perform specific tasks and can work together. Instead of using one elaborate program, you can combine several simpler ones, passing the output of one to the next.
Unix, Linux and macOS—the main differences
UNIX is also a trademark associated with certification administered by The Open Group. Certification confirms that a specific product meets the requirements of the standard. Similar behaviour or historical connections are not enough to automatically classify every system as certified UNIX.
| Name | What does it mean in practice? |
|---|---|
| Unix / UNIX | The historical system and its family, or, in the context of certification, a system that meets the requirements of the relevant standard. |
| Linux | Strictly speaking: a system kernel. In everyday usage: an operating system using that kernel, distributed as a distribution such as Debian or Ubuntu. |
| macOS | Apple’s operating system with Unix foundations and a graphical interface; certification applies to specific releases and configurations. |
| FreeBSD | A Unix-like system descended from the BSD line, separate from Linux. |
Linux was developed independently of the original Unix kernel, but follows its operating model. This means that many commands and skills can be transferred between Linux, macOS and other Unix-like systems. It does not mean they are completely interchangeable: tool options, service management, package installation and supported applications may differ.
If certification is a purchasing or project requirement, check the specific version and platform in The Open Group’s official register rather than relying on the system’s general name.
Does Unix mean working exclusively in the terminal?
No. A Unix system can have a graphical environment, with macOS being an everyday example. A terminal is an application that provides access to a text-based interface, while a shell, such as Bash or Zsh, interprets the commands you enter. The terminal, shell and operating system are different components.
For example, in a typical Unix environment, the command:
ls /etc
lists the names of visible files and directories in /etc, where system and service settings are usually stored. The command itself does not modify these files.
Tools can also be connected using a pipe, represented by the | character:
printf 'cat\ndog\ncat\n' | sort | uniq
The first command creates three lines of text, sort sorts them, and uniq removes adjacent duplicates. The result is two lines: kot and pies (Polish for “cat” and “dog”). This is a simple example of the Unix principle of small programs working together.
Why learn about Unix?
Understanding the Unix model helps with server administration, programming, automation and working with cloud services. It is also useful for website owners using Linux-based hosting: it makes it easier to understand paths, permissions and commands executed through SSH, an encrypted remote connection.
You do not need a commercial Unix system to learn. You can use the macOS terminal, a Linux distribution in a virtual machine or a Linux environment on Windows through WSL. Start by navigating directories and creating files in a separate practice directory, without administrator privileges.
See also: What is Linux?
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