Linux Stayin' Alive

What this Linux TCP keepalive timing question tests

This is a hard systems-level question that probes deep familiarity with TCP socket behaviour and kernel defaults. It's the kind of question that separates candidates who have read the standards and tuned production systems from those who have only worked at the application layer.

To answer it correctly, you need to know the specific kernel parameter that governs TCP keepalive timing, understand how it interacts with the TCP state machine, and be able to recall or reason about the typical default value on a standard Linux distribution. The answer is not theoretical—it's a concrete number that appears in /proc/sys/net/ipv4 and in the kernel source.

• TCP keepalive mechanism and idle-connection detection
• Kernel socket options and their defaults
• Difference between keepalive probes and application-level heartbeats
• Why firms care about these timings in low-latency and reliability contexts