Advanced Linux Performance and Services Questions

Advanced administration focused on service lifecycle, process management, and system performance. Topics include deep systemd service management and unit file authoring, dependency ordering and service recovery, process lifecycle and signal handling, cgroups and resource controls, tuning kernel parameters, diagnosing CPU and memory pressure, understanding page cache and swap behavior, out of memory scenarios, I O performance analysis, interpreting load average, and using performance and sampling tools such as top, htop, pidstat, iostat, vmstat, sar, and perf for identifying bottlenecks and implementing mitigations.

HardTechnical

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Hard: You find a process consuming large amounts of file descriptors and causing EMFILE errors globally. Propose a plan to debug where descriptors are coming from, short-term mitigations to restore service, and long-term design changes to prevent descriptor leaks. Include commands to gather evidence.

MediumTechnical

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Medium: Explain how to interpret 'sar -r' memory output vs /proc/meminfo. Which sar fields correspond to cached/buffered memory and how would discrepancies arise between sar and instantaneous /proc readings?

EasyTechnical

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Describe the structure of a systemd unit file and the purpose of its main sections (Unit, Service, Install). Provide an example of a minimal service unit for a simple HTTP server binary located at /usr/local/bin/myserver and explain each directive you included.

Example expected content: a code block with the unit file and a short explanation for each directive.

MediumTechnical

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You observe sustained high iowait on a host. Using iostat, vmstat, and pidstat, describe a concrete investigative sequence (commands and interpretation) to determine whether the bottleneck is per-device saturation, a single noisy process, or filesystem-level contention.

HardTechnical

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Hard: Provide a checklist and sequence of commands to produce a comprehensive performance packet for a single host after a reproducible 2-minute performance degradation window: include logs, perf data, iostat, sar, vmstat, top, and network stats. Explain how you ensure privacy/security when collecting traces from production.

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