---
title: vmstat — system load summary
date: 2026-10-18
time: 12:00
model: admin
category: programs
author_type: human
summary: A tool that periodically summarizes and shows CPU, memory, swap, and I/O status. Useful for identifying bottlenecks.
tags: program, Fault diagnosis and recovery, vmstat
---

**💬 "vmstat command"**

vmstat **summarizes CPU, memory, and I/O in a single line**. It quickly identifies where the bottleneck is.

Starting from the second line, the values are actual measurements; specify an interval to observe continuously.

- **r / b**: number of processes waiting to run / blocked.
- **si / so**: swap in/out. If not 0, it indicates memory pressure.
- **bi / bo**: block I/O. This is a disk bottleneck indicator.
- **wa**: percentage of CPU waiting on I/O. If high, it indicates a disk bottleneck.
## Frequently used options

| Option | Description |
| --- | --- |
| <interval> <count> | e.g., vmstat 1 5 (5 times at 1-second intervals) |
| -s | Memory-related statistics summary |
| -d | Per-disk statistics |
| -w | Wide output format |

## Three essential command combinations

- `vmstat 1 5` — system summary at 1-second intervals, 5 times
- `vmstat -s | head` — memory statistics summary
- `vmstat -d | head -5` — per-disk I/O statistics
**💬 "Just point out one pattern commonly used on real production servers"**

Here are common situations encountered on real production servers, organized step by step.

### Step 1 · Summary observation

Measure for a few seconds and observe the trend.

```
vmstat 1 5
```

### Step 2 · Identify the bottleneck

If si/so is high, it is memory; if wa is high, it is disk.

```
vmstat 1 5 | awk '{print $1,$2,$7,$8,$16}'
```

### Step 3 · Find the cause

Look at the process using that resource.

```
ps -eo pid,%cpu,rss,comm --sort=-rss | head
```

## How it is used in practice

### 1. Identifying I/O bottlenecks

**Situation** — The server is slow, but the CPU is idle.

```
vmstat 1 5
```

**Result** — If wa (wait) is high and bi/bo is large, it is a disk bottleneck.

**Point** — Use iostat to narrow down which disk, then identify the process.

### 2. Detecting swap usage

**Situation** — Check whether memory is insufficient.

```
vmstat 1 5 | awk 'NR>2{print $7,$8}'
```

**Result** — If si/so is not 0, swap is actually being used.

**Point** — Heavy swapping causes a sharp drop in performance.

## Things to keep in mind

- The first line is an average since boot, so do not use it as a measurement.
- A single run without an interval is a snapshot and misses trends.
- In containers, host-wide values may be displayed.
## Actual execution output

This is the result of observing CPU, memory, and I/O status at 1-second intervals.

![vmstat command execution result: system load summary](https://games.aidebatehub.com/assets/vmstat-demo.png)

Production server

---
Source (HTML): https://games.aidebatehub.com/programs/linux/troubleshooting/vmstat.html
This file is an auto-generated Markdown twin of the DevHub document.