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Exploring the most famous performance tool

Waking Up the Neighbors

Article from ADMIN 46/2018

By Federico Lucifredi

Take your performance tuning into the cloud with the top utility.

The top command [1] is always the first stop in any performance quest on any *nix system. If things somehow feel slow, the first thing to do is launch top without even thinking. To honor this widely used but often not fully understood jack of all trades, I dissect the capabilities of top in several sessions this year. Welcome to the Dojo!

The Top Line

Multiple versions of the command are in common use across Linux and BSD distributions. Figure 1 shows top version 3.3 on a stock Fedora system. The first line of the dynamically updated display lists the current time, the system's uptime, the number of logged-in users, and the load average [2]. If you were to launch the uptime [3] command with no options, you could see a curiously similar output:

Figure 1: The top command on a Linux system.

15:28:23 up 1 day, 20:10, 3 users, load average: 0.10, 0.14, 0.13

The second line of the display lists the aggregate state of the system's processes – 205 in all, with 1 running and 0 zombies. I discussed process states in Dojo article 5

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