LCA Performance Monitoring & Tuning 3

Question 1

Which command from the sysstat suite collects and reports historical system activity data on a scheduled basis?

Accepted Answer

sadc

Answer

sadc (System Activity Data Collector) is the backend daemon that records data later read by sar.

Question 2

What does the 'b' column in vmstat output represent?

Accepted Answer

Number of processes blocked waiting for I/O or other resources

Answer

The 'b' column in vmstat shows processes in uninterruptible sleep, typically waiting on I/O.

Question 3

Which command pins a process or command to specific CPU cores using a CPU affinity mask?

Accepted Answer

taskset

Answer

taskset sets or retrieves a process's CPU affinity, controlling which cores it may run on.

Question 4

What does 'iowait' percentage in top or mpstat specifically measure?

Accepted Answer

CPU time spent idle while at least one I/O request was outstanding

Answer

iowait is CPU idle time that occurs when the system has pending disk I/O, indicating potential I/O saturation.

Question 5

Which /sys path allows you to change the I/O scheduler for a specific block device at runtime?

Accepted Answer

/sys/block/<dev>/queue/scheduler

Answer

Writing a scheduler name (e.g., 'mq-deadline') to /sys/block/<dev>/queue/scheduler changes it live.

(LCA) Certified Linux Administrator Practice Test