Linux debugging tools I love - Julia Evans

Linux debugging tools I love - Julia Evans: "

strace
A tool that traces system calls. My favorite thing. I have a bunch of posts with examples of how to use it on this blog. If you want to read what I think of it you should read the fanzine reference that you can read here.

strace is pretty broadly useful, but keep in mind it can really slow down your programs.

I would be remiss if I did not mention the even-more-awesome dtrace. Colin Jones has a nice introduction.



 dstat
A really simple tool that prints out how much data got sent over the network / written to disk every second. This is great when you suspect something is going on with network/disk usage and want to see what's happening in real time.

There's also iostat and netstat and atop and a bunch of other tools, but dstat is my favorite.



 tcpdump + wireshark
For spying on network traffic. I wrote an introduction explaining how to use them in tcpdump is amazing.

When using these, it really helps to have a basic understanding of how networking works. Luckily the basics ("what's the difference between IP and TCP and HTTP? what's a network packet?") are totally possible to pick up :D.



 perf 

Have a C program and want to know which functions it's spending the most time in? perf is a sampling profiler for Linux that can tell you that.

perf top gives you a live view of which functions are running right now, just like top. I like to use perf top no matter what language my programs are written in, just to see if I can understand anything from it. Sometimes it works!

node.js has built-in support for using perf to show you which Node function is running right now. You can also get this for JVM programs with perf-map-agent.

Brendan Gregg's website has the best introduction to perf I know.

You can use perf to generate amazing flame graphs.



 opensnoop 

Opensnoop is a new script that you can get as of Ubuntu 16.04. It's a delightfully simple tool -- it just shows you which files are being opened right now on your computer. And it's fast, unlike strace!

opensnoop also exists on OS X and does basically the same thing.

Go to the iovisor/bcc repo on github for installation instructions. It works using eBPF, which is a new thing that I will not explain yet here but Brendan Gregg has been writing about enthusiastically for some time. You don't need to know how it works to use it, though :)."



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