LCA Performance Monitoring & Tuning 2

Question 1

Which command displays real-time per-CPU statistics including user, system, and idle percentages?

Accepted Answer

mpstat

Answer

mpstat from the sysstat package shows per-processor statistics in real time.

Question 2

What does a consistently high 'si' (swap-in) value in vmstat output indicate?

Accepted Answer

The system is actively swapping pages from disk to RAM, indicating memory pressure

Answer

High 'si' in vmstat means the OS is reading pages back from swap into RAM, a sign of insufficient physical memory.

Question 3

Which /proc file provides a summary of CPU time spent in user mode, kernel mode, idle, and iowait?

Accepted Answer

/proc/stat

Answer

/proc/stat contains cumulative CPU time counters used by tools like top and vmstat.

Question 4

You run 'perf stat ./myapp' and see a very low Instructions Per Cycle (IPC). What is the most likely bottleneck?

Accepted Answer

Memory latency or cache misses causing the CPU to stall

Answer

Low IPC typically means the CPU is stalling while waiting for data from cache or RAM.

Question 5

What is the purpose of 'nice' and 'renice' commands in Linux performance tuning?

Accepted Answer

Adjusting a process's scheduling priority to influence CPU time allocation

Answer

nice and renice set a process's niceness value, which affects its priority in the CPU scheduler.

(LCA) Certified Linux Administrator Practice Test