Linux is a family of ___________ operating systems.

Operating systems and other software are classified by their licensing model into two broad categories: open source, where the source code is published publicly and can be inspected, modified, and redistributed (often under a license such as the GNU General Public License, GPL), and closed source (proprietary), where the source code is kept private and only a compiled binary is distributed to users.

The Linux kernel is released under the GNU General Public License (GPL-2.0). Every major Linux distribution — such as Ubuntu, Fedora, and Debian — builds on this openly published kernel source, bundling it with many other open-source components released under a variety of open-source licenses (GPL, MIT, BSD, Apache, and others). Because the underlying code across the kernel and its ecosystem is published and modifiable rather than hidden, Linux is described as a family of open source operating systems.

• Closed source describes the opposite licensing model, where the source code is kept private — this is how many proprietary commercial operating systems work, not how Linux is distributed.

• Multi source is not a recognized software-licensing category; it does not describe whether an operating system's code is published or kept private.

• Time sharing source is not a licensing category either — time-sharing is a CPU-scheduling technique that lets a processor serve multiple users or processes, unrelated to whether the source code is publicly released.

Since Linux's source code is openly published and freely modifiable under the GPL, the correct classification is open source.