How do you troubleshoot high CPU or memory usage on Linux?
Assesses fundamental understanding of Linux Administration conventions, runtime behavior, and memory/performance considerations.
Hiring managers look for precision, avoidance of ambiguous jargon, and ability to explain trade-offs under real production conditions.
Identify the consumer before acting.
CPU:
top -o %CPU
uptime # load average
pidstat 1 5 # per-process CPU
perf top # hot functions
Check load average against core count. High load with low CPU often means I/O wait. Look at runnable versus blocked processes, and check for CPU steal on virtual machines.
Memory:
free -h
vmstat 1 5
ps -eo pid,rss,cmd --sort=-rss | head
cat /proc/<pid>/status | grep -i vm
Distinguish buff and cache from used memory; Linux uses free RAM for caching. Check for OOM kills in dmesg or journalctl -k. Look for swap thrashing, visible as high si and so in vmstat.
Then profile the application, check for leaks, tune limits, or right-size the instance. Use cgroups to cap runaway processes.
Candidate Response Strategy & Interview Tips
- Start with a concise one-sentence summary: Deliver a direct, confident answer first before expanding into nuances.
- Demonstrate real-world trade-offs: Discuss where this approach excels and when you would avoid it in production systems.
- Discuss complexity & edge cases: Proactively explain time/space complexity or boundary conditions (null values, scale limits).
- Prepare for interviewer follow-ups: Technical hiring panels frequently probe deeper into concurrency, backward compatibility, or alternative libraries.