Understanding system performance is crucial for maintaining stable and efficient operations. A fundamental utility available on most systems provides deep insight into various resource statistics, proving invaluable for diagnosing bottlenecks and monitoring system health. This tool focuses particularly on virtual memory, but also covers processes, paging, block I/O, traps, and CPU activity.
The output of this command is typically organized into several key sections:
Procs: This section reports on processes.
- r: The number of processes waiting for run time. A consistently high number here can indicate a CPU bottleneck.
- b: The number of processes in uninterruptible sleep. This is often associated with I/O waiting.
Memory: This part details memory usage.
- swpd: The amount of used swap memory. High values and active swapping often point to insufficient physical memory.
- free: The amount of idle memory.
- buff: Memory used as buffers.
- cache: Memory used as cache. The free, buff, and cache values collectively represent available memory.
Swap: This shows the rates of swapping activity.
- si: The amount of swap into memory (KB/s).
- so: The amount of swap out to disk (KB/s). Sustained high si and so rates are strong indicators of a system heavily relying on swap, signaling potential memory pressure.
IO: This section reports on block I/O activity.
- bi: Blocks in (received from a block device, KB/s).
- bo: Blocks out (sent to a block device, KB/s). High values here indicate significant disk activity, which could be a bottleneck.
System: This covers system-wide events.
- in: The number of interrupts per second.
- cs: The number of context switches per second. High numbers for both can indicate a very busy system.
CPU: This is a breakdown of CPU time utilization.
- us: Percentage of CPU time spent on user processes.
- sy: Percentage of CPU time spent on system (kernel) processes.
- id: Percentage of CPU time spent idle.
- wa: Percentage of CPU time spent waiting for I/O. A high wa value suggests that the CPU is frequently waiting for disk operations to complete, pointing towards an I/O bottleneck.
- st: Percentage of CPU time stolen from a virtual machine by the hypervisor (relevant in virtualized environments).
By regularly observing the output of this command, especially over time using an interval and count, system administrators and performance analysts can gain valuable insights. For instance, high r values might require investigating CPU usage, while high swpd or si/so suggests a need for more RAM. High bi/bo or wa indicates issues with disk performance. Mastering the interpretation of these metrics is fundamental to effective system monitoring and performance tuning.
Source: https://www.linuxlinks.com/vmstat-reports-virtual-memory-statistics/
