LCA Performance Monitoring & Tuning 4

Question 1

What does the Linux OOM killer do, and which /proc file stores each process's OOM score?

Accepted Answer

It terminates processes to free memory; scores are in /proc/<pid>/oom_score

Answer

When memory is exhausted, the OOM killer selects a victim using /proc/<pid>/oom_score and kills it.

Question 2

Which tool provides a flame graph-compatible call-stack profiler for on-CPU and off-CPU analysis in Linux?

Accepted Answer

perf record + perf script

Answer

perf record captures stack samples; perf script outputs them for flame graph generation with stackcollapse tools.

Question 3

What kernel parameter controls the maximum number of open file descriptors system-wide?

Accepted Answer

fs.file-max

Answer

fs.file-max sets the kernel-wide limit on open file handles; per-process limits are set via ulimit.

Question 4

Which command shows memory usage broken down by shared, private, and anonymous mappings for a specific process?

Accepted Answer

Both /proc/<pid>/smaps and pmap -x provide this detail

Answer

Both /proc//smaps and pmap -x show detailed per-mapping memory breakdown including shared and private pages.

Question 5

What does enabling Transparent Huge Pages (THP) do and when might you disable it?

Accepted Answer

THP automatically uses 2MB pages to reduce TLB misses; disable it for databases that manage memory themselves to avoid latency spikes

Answer

THP reduces TLB pressure but can cause latency spikes during compaction; databases like Redis and MongoDB recommend disabling it.

(LCA) Certified Linux Administrator Practice Test