---
title: watch — monitor repeated output
date: 2026-10-18
time: 12:00
model: admin
category: programs
author_type: human
summary: A tool that repeatedly runs a command at regular intervals and continuously displays changes on the screen.
tags: program, Automation and scheduled tasks, watch
---

**💬 "watch command"**

watch **periodically re-executes a command** and shows changes. It is convenient for observing progress.

The default interval is 2 seconds, and you can adjust it with -n.

- **Concept**: Periodically refreshes and displays command output.
- **-n**: Specifies the interval in seconds.
- **-d**: Highlights changed parts.
- **Top**: Shows the running command and the current time.
## Commonly Used Options

| Option | Description |
| --- | --- |
| -n <seconds> | Specifies the refresh interval |
| -d | Highlights differences |
| -t | Hides the top header |
| -g | Exits when output changes (for scripts) |

## Three Essential Command Combinations

- `watch -n 2 'ss -lntp | grep :443'` — Observe port 443 status
- `watch -d -n 1 'df -h /var'` — Observe changes in disk usage
- `watch -n 5 'pgrep -c -f queue:work'` — Observe changes in worker count
**💬 "Tell me examples I can use even with an unprivileged account"**

Here are common situations on live production servers, arranged in order.

### Step 1 · Start Observing

Wrap the command you want to check with watch.

```
watch -n 2 'ss -lntp | grep :443'
```

### Step 2 · Highlight Changes

Use -d to highlight differences.

```
watch -d -n 1 'df -h /var'
```

### Step 3 · Exit

When you're done, press Ctrl+C to exit.

```
Ctrl+C
```

## How It Is Used in Practice

### 1. Observing Connection Count During Deployment

**Situation** — You want to see how active connections change during deployment.

```
watch -n 2 "ss -s | grep estab"
```

**Result** — You can monitor changes in the active connection count in real time.

**Point** — Compare baseline values before and after deployment to judge sudden drops or spikes.

### 2. Checking Disk Growth Trend

**Situation** — You want to know how fast logs are filling up.

```
watch -d -n 5 'df -h /var && du -sh /var/log/nginx'
```

**Result** — The highlighted values let you immediately sense the growth rate.

**Point** — Use the growth rate to decide the log rotation interval.

## Things to Watch Out For

- If the interval is too short, it can cause load, so adjust -n.
- Commands inside watch go through the shell, so be careful with quoting.
- For automated decisions, use a condition-checking script rather than watch.
## Actual Output Screen

This is the result of observing TCP connection status every 2 seconds.

![watch command execution result: repeated observation of connection status](https://games.aidebatehub.com/assets/watch-demo.png)

Live production server

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