iotop

top (pictured below... above is btop) is the first utility everyone recommends to monitor Linux (or any form of UNIX, including macOS) resource usage. It's efficient, available almost everywhere... but it's also a bit basic. It shows essential metrics, but looks like it's from the 80s. There are ways to brighten it up, like highlighting active processes or changing color schemes, but it's not the only game in town!

Nowadays, there are a lot of modern monitoring tools—and some not so modern, but immensely useful—to choose from. This blog post will run through some of the ones I rely on most often. Let me know in the comments if you use any others I didn't cover!

One one small LEMP VPS I manage, I noticed munin graphs that showed anywhere between 5-50 MB/second of disk IO. Since the VM has an SSD instead of traditional spinning hard drive, performance wasn't too bad, but all that disk I/O definitely slowed things down.

I wanted to figure out what was the source of all the disk I/O, so I used the following techniques to narrow down the culprit (spoilers: it was MySQL, which was using some swap space because it was tuned to use a little too much memory).

iotop

First up was iotop, a handy top-like utility for monitoring disk IO in real-time. Install it via yum or apt, then run it with the command sudo iotop -ao to see an aggregated summary of disk IO over the course of the utility's run. I let it sit for a few minutes, then checked back in to find: