atop Command: Tutorial & Examples

Monitor system resources in real-time

The atop command is a powerful tool in the Linux system administrator's arsenal. It provides a live, rolling view of system resources, making it an invaluable resource when monitoring system performance. Unlike other system monitoring tools, atop has the ability to report on all processes, even those that have completed during the interval, making it a superior choice for spotting short-lived processes.

The atop command works by collecting information from various system resources at regular intervals (default is 10 seconds, but this can be adjusted). The data is presented in a user-friendly format, making it easy to assess the state of the system at a glance.

Why is the atop command important?

The atop command is particularly useful for diagnosing high load situations where it's not immediately apparent what is causing the strain on system resources. By offering a comprehensive overview of system activity, atop allows administrators to identify problematic processes and take appropriate action.

Common problems solved by atop

Identifying resource-hungry processes: If your system is running slow, atop can help identify the processes that are consuming the most resources.
Monitoring system performance over time: atop can be used to log system performance over an extended period, making it easier to spot trends or potential issues.
Troubleshooting system crashes: If your system has experienced a crash, atop logs can provide valuable insight into what was happening on the system just before the crash occurred.

How to use atop

To start using atop, simply type atop in your shell and press enter:

atop

This will start atop with the default interval of 10 seconds. The information displayed includes CPU usage, memory usage, disk I/O, network activity, and more.

To change the interval to 5 seconds:

atop 5

This will refresh the atop display every 5 seconds.

To log system performance for a specific duration, use the -w option with a file path and the duration in seconds:

atop -w /tmp/atop.log 60

This will write atop data to /tmp/atop.log every 60 seconds.

Common command line parameters

-r: Read from a previously saved log file.
-w: Write the output to a file for later analysis.
-d: Display details for processes in a specified format.
-h or --help: Display help information for the command.

Typical output of atop

A typical output of the atop command looks like this:

ATOP - hostname  15:24:36  up  1:14,  1 user  loadavg: 0.06, 0.02, 0.00
PRD  SECS  CPU  %usr %sys %irq %idle  |  MEM  tot   used  free  buff  cache  |  DSK  read  write  |  NET  recv  send
1    60    cpu   2    1    0   97    |  mem  1.9G  628M  1.3G  35M   287M  |  dsk  0.0   0.0    |  net  0.0   0.0

Here, PRD is the interval duration, SECS is the number of seconds since atop started, CPU shows the CPU usage, MEM shows memory usage, DSK shows disk I/O, and NET shows network activity.

Potential problems and pitfalls

While atop is a powerful tool, users should be aware of certain limitations:

Resource consumption: Running atop for extended periods may consume additional system resources. Use the -d option to control the level of detail displayed.
Log file size: If logging is enabled, log files can become quite large over time. Regularly monitor and manage log file sizes.
Understanding output: New users may find the output overwhelming. Familiarize yourself with the layout and terminology to make effective use of the tool.