Analyzing Linux server performance with atop

We’re all familiar with top, a real-time system monitor which shows usage of your Linux hardware and network resources. As a top command alternative, atop also provides sysadmins with real-time system insight, and also allows for an anatomized view of which processes are using the most CPU, memory, storage, or network.

Let’s take a look at using atop for Linux server performance analysis.

Advantages of atop

Atop is an ASCII, full-screen performance monitor which can log and report the activity of all server processes. One feature I really like is that atop stays active in the background for long-term server analysis (up to 28 days by default). Other advantages include:

• Shows resource usage of all processes, even those that are closed or completed.
• Monitors threads within processes and ignores processes that are unused.
• Accumulates resource usage for all processes and users with the same name.
• Highlights critical resources using colors (red).
• Adds or removes columns as the size of the display window changes.
• Includes disk I/O and network utilization.
• Uses the netatop kernel module to monitor TCP, UDP, and network bandwidth.

Once atop is launched, by default it shows system activity for CPU, memory, swap, disks, and network in 10-second intervals. In addition, for each process and thread, you can analyze CPU utilization, memory consumption, disk I/O, priority, username, state, and even exit codes:

Install atop on Red Hat Enterprise Linux/CentOS/Fedora Linux

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First, install and enable the Extra Packages for Enterprise Linux (EPEL) repo. See Red Hat solution #308983 if you’re not sure how to do this. Once that task is complete, you can install atop:

yum install atop

Launch it similar to top, using:

atop

Using atop

When it comes to using atop, a good place to start is to read the man pages:

man atop

Useful atop launch commands include:

Once atop is running, press the following shortcut keys to sort processes:

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Reading atop reports and logs

By default, after installation, the atop daemon writes snapshots to a compressed log file (e.g., /var/log/atop/atop_20140813). These log files can be read using:

atop -r </full/path/to/atop/log/file>

Once you open a log file (e.g., atop -r /var/log/atop/atop_20140813), then use t to go forward in 10-minute intervals, and T to go back. You can analyze specific times by pressing b and then entering the time. The above shortcut keys also work in this mode: a, c, d, m, and n.

You can use shortcuts with atopsar. For example, using the flag -c 30 5 with atopsar generates a report for current CPU utilization for five minutes (10 times with intervals of 30 seconds):

atopsar -c 30 5

Using the flag -A with return all available reports.

atopsar -A

But, you can limit this output to a specific time window using beginning (-b) and end (-e) flags:

atopsar -A -b 11:00 -e 11:15

Wrapping Up

There are some good advantages and unique features of atop, as listed above. Personally, I like how atop allows you to isolate and analyze CPU usage, memory consumption, storage I/O, etc., for each process and thread.

Still, some of us will continue to prefer top or htop, and they are both great tools. After reading this article, I hope more people will also add or continue to use atop as one of their go-to Linux analysis and troubleshooting tools.