What Is Linux, and What Does the Linux Kernel Do?

Key takeaways

• The kernel is the core of the system. Linux strictly names the kernel; people also use it for the whole operating system.
• A distribution is the kernel plus GNU tools, libraries, an installer and a package manager.
• The kernel manages processes, memory, files, devices and networking, and enforces security.
• Check your kernel with uname -r and see loaded modules with lsmod.
• CentOS Linux is end-of-life. Rocky Linux and AlmaLinux are RHEL-compatible alternatives.

What is Linux?

Strictly speaking, Linux is a kernel: the central program of an operating system. In everyday talk, "Linux" means a whole operating system built around that kernel. Linus Torvalds began the kernel in 1991 as a student project. It was combined with tools from the GNU project, which is why some people say GNU/Linux. The result is free software: you can read, change and share the source code under licences such as the GPL. Linux is a Unix-like system, meaning it follows the Unix design of files, processes and permissions, but it is not the same as Unix. Linux powers most web servers, nearly all supercomputers, Android phones and a large part of the cloud.

What is the Linux kernel?

The kernel sits between hardware and programs. Applications ask the kernel for services through system calls, such as opening a file or sending data over the network. The kernel decides who gets the CPU, memory and devices, and keeps programs from interfering with each other.

What does the kernel do?

What is the difference between Linux and a Linux distribution?

A distribution (distro) packages the kernel with everything else you need: the GNU command-line tools, a C library, a service manager such as systemd, a package manager, a desktop environment if wanted, default settings and an update service. Different distros make different choices.

• Debian and Ubuntu: use apt and .deb packages.
• Red Hat Enterprise Linux (RHEL), Fedora, Rocky Linux and AlmaLinux: use dnf and .rpm packages.
• Arch Linux: a rolling release for people who like to build their system.

CentOS Linux, once a popular free rebuild of RHEL, is end-of-life. CentOS Stream continues, and Rocky Linux and AlmaLinux are the RHEL-compatible rebuilds. Red Hat's current release is documented at docs.redhat.com.

How do you check your kernel?

uname -r # kernel release, for example the version string
uname -a # full system information
cat /proc/version # kernel build details
lsmod # loaded kernel modules
dmesg | tail # recent kernel messages

The kernel version in a distro is not the same as the newest version on kernel.org. Enterprise distributions such as RHEL ship a specific kernel version and backport fixes into it for the life of the release.

What are kernel modules?

Modules are pieces of kernel code, mostly drivers, that can be loaded and unloaded while the system runs. lsmod lists them, modinfo describes one and modprobe loads it. This is how a new USB device or file system gets support without a reboot.

Is Linux the same as Unix?

No. Unix is a family of operating systems that goes back to the 1970s. Linux was written from scratch to behave like Unix, so many commands and ideas carry over. This is why skills from Linux transfer to systems like FreeBSD or macOS to a degree.

Common misunderstandings

• "Linux is an operating system you download." You download a distribution.
• "Free means no support." Companies sell support for enterprise distributions.
• "A newer kernel is always better." For servers, stability and vendor support often matter more.

Next steps

Read the Linux kernel's importance and key features and the Linux administrator career roadmap. To learn hands-on, join our Linux course.

Related reading

• How to Become a Master in Linux? The Open-Source Revolution
• Why Linux is the Most Popular Operating System?