PhonePe Linux, Networking & Scripting interview questions

The question that reveals whether someone knows what load average actually counts on Linux. It is not a CPU metric, and that single fact resolves the whole thing.

The classic ephemeral port exhaustion question. TIME_WAIT is a familiar phrase and the useful facts are narrower: which side accumulates it, and why the popular fix is dangerous.

Interviewers use this to sort memorised trivia from people who have chased a slow lookup. Three roles, one bit, and the caching rules most candidates repeat incorrectly.

Everyone knows ulimit -n. The interview question is which process inherits which value, why limits.conf did nothing for your service, and how you size the ceiling honestly.

One round trip versus two is the headline, but the ops-relevant differences hide in what stays plaintext, how resumption works, and which middlewares the change broke.

A reset at a suspiciously round number is a fingerprint, not a bug. Matching client keepalives to the lowest timer in the path is the fix; here is the full ladder of knobs.

Transparent versus explicit hugepages is a control question, not a size question. Fork-heavy stores suffer THP copy-on-write amplification while large-resident databases gain TLB reach.

The question that separates people who have debugged a hung rollout from people who have read about one. The interesting half is not the signal, it is PID 1.

Ordering and retransmission are what TCP adds, and both of them cost time. Naming something that deliberately gives them up, and saying why, is what turns a textbook answer into a real one.

A staple of every networking round, and the follow-up is always about TLS termination. Knowing which layer sees what decides most of the answer.

The oldest question in systems interviewing and still the best, because it is unbounded: every layer you can describe is another layer you could debug.

Five stages, and which one you are stuck in tells you what to fix. A machine that reaches a GRUB prompt has a different problem from one that hangs waiting on a filesystem that no longer exists.

The arithmetic takes thirty seconds to learn and gets asked constantly. What it is really testing is whether you have ever had to size a VPC that could not be resized later.

Most of what looks like used memory on a healthy Linux box is page cache doing its job. Knowing which column to read, and why df and du disagree, is half of Linux triage.

A growing backlog of sockets waiting for the application to close its side usually points at lifecycle handling. Here is the hunt from ss output to the pool timeout that caused it.

Most hand-written units boot in dev and die in production. The gap is Type selection, restart policy, and the drop-in workflow vendors expect you to respect.

A one-line mistake that locks you out of the obvious fix. The fast recovery teaches more about the permission model than any man page will.

Two authentications happen in every SSH session, and the one usually left out is the server proving itself to you. Knowing who proves what, and where your agent socket ends up, is the scored material.

The scripting round in disguise. The constraint is the question: it exists to see whether you stream or whether you load, and everything else is about whether the script is safe to run twice.

The two-syscall duet behind every process on the box. The follow-ups live in what survives the transition, and candidates who skip that fail the next question.

The answer is yes, and then the real question starts. Asymmetric routing and silent drops punish anyone who treats the routing tables as one flat list.

The flags are the easy part. The scored part is proving you can capture on a saturated box without adding load, then read the file afterward like evidence.