# Knowledge Check: Processes

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**1. What does a PID identify?**

*Answer:* One specific running instance of a program — the kernel's unique identifier for that
process, distinct from every other running process, even other copies of the same program.

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**2. What's the actual difference between `kill <pid>` and `kill -9 <pid>`?**

*Answer:* Plain `kill` sends SIGTERM, a polite request the process can choose to handle (clean
up, then exit). `kill -9` sends SIGKILL, which the kernel enforces immediately with no chance
for the process to react — an escalation for when SIGTERM is ignored, not the default choice.

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**3. You want to confirm a process is still running WITHOUT affecting it in any way. What do
you use?**

*Answer:* `kill -0 <pid>` — sends no real signal, only checks whether the PID still exists.

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**4. Why might understanding processes matter for understanding containers later?**

*Answer:* A container is, underneath, mostly an isolated process (or small process tree) — a
container "exiting" is really its main process exiting, the exact same event this module's Lab
causes on purpose.

## Instructor Notes

**Facilitation:** Question 2 is worth confirming explicitly — "kill -9 by default" is a common,
worth-correcting habit.

**Approximate timing:** 5 minutes.