It is 3am and you get paged: the primary application server is at 100% disk usage and the app is throwing write errors. You are the only one online. Walk me through exactly what you do.
What they are really testing: They want to see whether you can restore service safely under pressure without deleting something you cannot get back. Panic deletion of the wrong file is the classic junior failure here.
A real interview question
It is 3am and you get paged: the primary application server is at 100% disk usage and the app is throwing write errors. You are the only one online. Walk me through exactly what you do.
What most people say
drag me
“I would SSH in and delete the biggest files I can find to free up space, then go back to sleep.”
It jumps straight to a destructive action with no idea what the files are, and it never verifies the service actually recovered or explains why the disk filled.
The follow-ups they ask next
You freed 20GB but df -h still shows the disk full. What now?
Say the words deleted-but-open file handle, then reach for lsof +L1 and restart the holding process.
Why alert at 80 percent instead of 100 percent?
Explain that you want time to act, and that a full disk is a hard failure, not a degradation.
What the interviewer is listening for
- Confirms with df before touching anything
- Knows the deleted-but-open file handle trap
- Verifies recovery on a dashboard, not just on the shell
- Escalates instead of repeatedly deleting
What sinks the answer
- Deletes files without knowing what they are
- Never mentions verifying the app recovered
- Treats the page as done once space is free, with no follow-up
- Refuses to wake anyone even when growth is unexplained
If you genuinely do not know
Say this instead of freezing. Reasoning out loud from what you do know beats silence every single time, and a good interviewer is listening for exactly that.
“I have not been paged for this exact thing, but here is how I would reason about it: confirm which filesystem is full, free space from the provably safe stuff first, then find what is growing and why.”
Keep going with troubleshooting
Junior
You get paged at 2am. Checkout latency has gone from 200ms to 4 seconds and it started right after the 11pm deploy. Walk me through what you do.
Junior
You push a new version of a service and within two minutes the pods are all showing CrashLoopBackOff. The team is watching you share your screen. Walk me through exactly what you do.
Junior
A developer pings you: the checkout service cannot reach the payments service, the calls just hang and time out. You have never worked on either service. Walk me through what you do.
Junior
A developer messages you: 'My app suddenly gets Access Denied writing to the S3 bucket. Nothing changed.' It worked yesterday. Walk me through what you do.
Mid
Your load balancer shows 5xx errors jumping from 0.1 percent to 12 percent of requests over ten minutes. There was no deploy. What do you do?
Mid
One of your containers keeps getting OOM killed. It restarts, serves traffic for about twenty minutes, then dies again. Talk me through how you handle it.
Knowing the answer is not the same as recalling it under pressure
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