# Monitoring resource usage

> Monitor CPU, memory and process activity on a server in real time with the top and atop commands.

Source: https://helpcenter.ruachost.com/developers/linux/monitoring-resource-usage/

**Monitoring resource usage**\
Learn how to monitor system resource usage using the `top` and `atop` commands.

This article explains how to track resource usage on a server with `top` and `atop`.

**Method #1: Use the top command**\
The traditional way to view resource usage on Linux is with the `top` program. `top` provides a real-time overview of system information and running processes, and you can customize the displayed data.

To start `top`, log in via SSH and run:

```
top
```

By default, `top` refreshes every 3 seconds. You can manipulate the display in many ways; for example, press `P` to sort tasks by CPU usage.

For detailed information on `top`, run:

```
man top
```

**Method #2: Use the atop command**\
`atop` is similar to `top` but offers additional features. It provides a real-time summary with more detailed information and multiple ways to view and filter it. `atop` also maintains background system activity logs, allowing you to view past resource usage.

To start `atop`, log in via SSH and run:

```
atop
```

When first started, `atop` may display a lot of information. Key parts of the display include:

- **Top line:** Server name, date, and time of the last sample
- **PRC row:** General statistics, including time in system calls (`sys`) and user space (`user`), number of processes (`#proc`), and zombie processes (`#zombie`)
- **CPU and cpu rows:** CPU statistics, showing time spent on system calls, user processes, interrupts (`irq`), idle, and waiting for disks (`cpuXXXw`)
- **CPL row:** Weighted load averages for the past 1, 5, and 15 minutes, plus context switches (`csw`)
- **MEM row:** Memory usage
- **SWP row:** Swap memory usage
- **PAG row:** Paging frequency
- **DSK row:** Disk usage
- **NET rows:** Network interface usage

For full reference on `atop`, run:

```
man atop
```

**View server activity history**\
`atop` maintains activity logs for the past few days. You can load historical data to investigate system performance issues.

- To view today's activity:

```
atop -r
```

- Move forward through history with `t` (lowercase) and backward with `T` (uppercase).
- To start at a specific time, use the `-b` option, e.g., to start at 10:15 today:

```
atop -r -b 10:15
```

- To view past days, list files in `/var/log/atop` and load the desired log file, e.g., March 16, 2025:

```
atop -r /var/log/atop/atop_20250316
```

## Tip

- To quickly view yesterday's resource usage:

```
atop -r y
```

- To view the day before yesterday:

```
atop -r yy
```