Intro

Updated

September 4, 2026

Intro

Measure subsystem health over time and debug why a host is slow or stuck: virtual memory, disks, CPUs, open files, and syscall/library traces.

Commands in this part

Command Role
vmstat vmstat reports virtual memory, process run/block queues, CPU, and I/O counters in a compact table.
iostat iostat (from the sysstat package) reports CPU utilization and per-device I/O rates, queue depth, await, and utilization.
mpstat mpstat (sysstat) reports CPU utilization, optionally per logical CPU, so you can see single-thread bottlenecks,…
sar sar (System Activity Reporter, sysstat) prints live and historical metrics: CPU, memory, load, disk, network, and more.
lsof lsof lists open files.
strace strace traces system calls and signals for a process.
perf perf is Linux’s primary performance analysis suite.
btop btop is a modern, interactive resource monitor with a polished TUI: CPU (often per-core with clocks/temps when…
ltrace ltrace intercepts and prints dynamic library calls of a process (similar to how strace prints syscalls).

Suggested starting points

  1. Load vs I/O vs CPU: vmstat, iostat, mpstat, sar.
  2. Who holds a file or port: lsof.
  3. Why a process fails: strace (syscalls), ltrace (library calls).
  4. Hotspots: perf (and interactive btop for a dashboard).