vmstat

Overview

The vmstat (virtual memory statistics) command reports statistics about system processes, memory, paging, block I/O, traps, and CPU activity. It’s an essential tool for system performance monitoring and troubleshooting.

Syntax

vmstat [options] [delay [count]]

Common Options

Option Description
-a Display active/inactive memory
-f Display number of forks since boot
-m Display slabinfo
-n Display header only once
-s Display memory statistics
-d Display disk statistics
-p partition Display partition statistics
-S unit Display specific unit sizes
-t Add timestamp to output

Key Use Cases

  1. System performance monitoring
  2. Memory usage analysis
  3. CPU utilization tracking
  4. I/O bottleneck identification
  5. System load assessment

Examples with Explanations

Example 1: Basic Usage

vmstat 2 5

Display stats every 2 seconds, 5 times

Example 2: Memory Statistics

vmstat -s

Show detailed memory statistics

Example 3: Disk Statistics

vmstat -d

Display disk I/O statistics

Understanding Output

Columns explained: - Procs: - r: runnable processes - b: processes in uninterruptible sleep - Memory: - swpd: virtual memory used - free: idle memory - buff: memory used as buffers - cache: memory used as cache - Swap: - si: memory swapped in - so: memory swapped out - IO: - bi: blocks received from device - bo: blocks sent to device - System: - in: interrupts per second - cs: context switches per second - CPU: - us: user time - sy: system time - id: idle time - wa: I/O wait time

Common Usage Patterns

  1. Real-time monitoring:

    vmstat 1

  2. Check memory stats:

    vmstat -s | grep memory

  3. Monitor swap usage:

    vmstat -w 2

Performance Analysis

  • First line shows averages since boot
  • Subsequent lines show interval statistics
  • High ‘wa’ indicates I/O bottleneck
  • High ‘r’ suggests CPU contention
  • Monitor swap activity (si/so)

Additional Resources