Quiz Entry - updated: 2026.07.14
What is the difference between static, dynamic, and runtime content in the Linux filesystem?
Filesystem content splits three ways by how it changes: static (only when you modify it), variable (changes as the system runs), and runtime (created at boot, gone at shutdown).
This isn't trivia — it's the principle that explains where a directory should live and on what kind of storage. Each category has different write needs:
| Type | Changes when… | Examples |
|---|---|---|
| Static | Only when you install/edit | /bin, /boot, /etc, /usr |
| Variable | Continuously, on its own | /var/log, /var/cache, /home |
| Runtime | Born at boot, cleared at shutdown | /run, /tmp |
Why the distinction pays off:
- Static content never changes during operation, so it can sit on read-only media or be shared read-only across many machines — great for security and for network booting.
- Variable content must be on writable, sized-for-growth storage, and is what you back up.
- Runtime content is disposable, so it can live in RAM (tmpfs) for speed, with nothing lost when it's wiped.
Takeaway: "how often does this change?" determines the storage strategy. That's why a hardened appliance can mount most of the system read-only and only allow writes to /var and /run.
Go deeper:
Filesystem Hierarchy Standard 3.0 — formalizes the static-vs-variable distinction underpinning where each directory lives.