Linux, the kernel and distributions (011.1)
Linux is a kernel: the core program that manages the processor, memory, devices and running programs, and that every other program asks when it needs the hardware. Linus Torvalds released the first version in 1991, and the kernel is licensed under the GNU General Public License version 2. A kernel alone is not usable, so it is combined with a userspace: a shell, system tools (many from the GNU project), libraries, a service manager such as systemd, and applications. A kernel and userspace packaged and tested together, with an installer and a package manager, is a distribution, or distro.
| Part | What it is | Examples |
|---|---|---|
| Kernel | Manages hardware, memory, processes and devices, in a protected mode | The Linux kernel |
| Userspace | Everything outside the kernel that users and services run | The Bash shell, GNU core utilities, systemd, libraries, a desktop environment, applications |
| Distribution | A kernel plus userspace, an installer, a package manager and a support policy | Debian, Ubuntu, Fedora, Red Hat Enterprise Linux, openSUSE, Alpine |
Distribution families
| Family | Members | Package tools | Typical use |
|---|---|---|---|
| Debian-based | Debian GNU/Linux, Ubuntu, Raspberry Pi OS | dpkg, apt, apt-get (.deb packages) | Desktops, cloud servers, the Raspberry Pi |
| Enterprise Linux (Red Hat-based) | Red Hat Enterprise Linux (RHEL), AlmaLinux, Rocky Linux, Fedora Linux, CentOS Stream | rpm, dnf (.rpm packages) | Company servers with long, often paid, support |
| SUSE-based | SUSE Linux Enterprise, openSUSE Leap, openSUSE Tumbleweed | rpm, zypper | Enterprise servers and desktops |
| Alpine Linux | Alpine, with its main and edge branches | apk | Very small and security-minded; a popular base for containers |
Inside the Enterprise Linux family, Fedora is where new features appear first, CentOS Stream is the development line just ahead of the next RHEL release, and AlmaLinux and Rocky Linux are free distributions built to be compatible with RHEL. openSUSE Leap is the stable, versioned openSUSE; Tumbleweed is its rolling release.
Release types and life cycles
| Release type | Meaning |
|---|---|
| LTS (long-term support) | A release supported with security fixes for years. Ubuntu publishes an LTS every two years with five years of standard security maintenance. |
| Stable | Tested and frozen; only fixes are added. Debian's stable release is currently Debian 13, code name trixie. |
| Testing | The next stable release being prepared; Debian's is currently forky. |
| Unstable | Where new packages land first. Debian's unstable branch is always called sid. |
| Rolling | No big version jumps; packages are updated continuously, as in openSUSE Tumbleweed and Alpine edge. |
| Alpha and beta | Pre-release test versions, not meant for production. |
| Interim releases | Shorter-lived releases between LTS versions; Ubuntu's interim releases get nine months of updates. |
Life cycles matter at work. A server should run a release that will receive security updates for its whole planned service life. When a release reaches end of life it stops getting patches and must be upgraded or replaced.
Android and Linux
Android uses the Linux kernel, with Google's changes, but not the usual GNU userspace: its apps run on the Android Runtime and use Android's own libraries. So Android is built on Linux, but it is not a typical Linux distribution, and Linux desktop programs do not run on it directly.
Debian's unstable branch is always named sid, whatever the stable release is called. And today's CentOS Stream is not the old CentOS Linux: it now sits just ahead of RHEL instead of rebuilding it.
If your voucher is for version 1.6 (010-160): the older objectives name individual distributions instead of families, including Linux Mint, Scientific Linux, Raspbian, CentOS and openSUSE, and they place distribution life cycles under topic 4.
Word bank
All definitions →- Distribution
- A complete operating system built around the Linux kernel
- End of life
- The date a release stops receiving security updates
- Kernel
- The core of the operating system that controls hardware and processes
- LTS
- Long-term support: a release maintained with fixes for several years
- Rolling release
- A distribution updated continuously instead of in numbered versions
- Userspace
- All the programs and libraries that run outside the kernel
Knowledge check
Which distribution uses apk as its package manager and is a common base image for containers?
A company needs a server operating system that will receive security updates for five years without major upgrades. Which release type fits?
Which statement about Android is correct?