What is your favorite open source debugging tool?

Question

I've been giving a talk recently on a plethora of Open Source (some are borderline open-source, I'll admit) debugging tools and the audiences have been making great additions to my list.

I'd like to gather the knowledge (and give credit) to the oft-brilliant StackOverflow crowd on this same question.

There are no WebService/Java/.Net/HTML/Perl constraints of programming languages to this question. So far, I've been pontificating about:

1. fs_usage for finding what keeps writing to disk so much
2. lsof for debugging what ports or files are open
3. tcpdump, wireshark, eavesdrop for looking at your network traffic (malformed data?)
4. firebug for debugging css, javascript, and page loading issues
5. SoapUI, poster, and for troubleshooting SOAP and RESTful web services
6. Eclipse Memory Analyzer and VisualVM for Java memory usage and GC issues
7. BTrace for instrumenting Java code already deployed to production servers
8. curl for looking at raw HTML, sans browser redirects, and test-calling web services
9. JMeter for load testing webapps and other supported components that fail under stress

What Open Source tools can you add to the list?

Answer 1

For the gcc crowd, there's gdb and gprof. I've gotten a lot done with those two.

Answer 2

xdebug for PHP can be a godsend.

Answer 3

gdb is the king of course, and valgrind has its fans.

For a nice open source GUI wrapper around gdb, see DDD. And yet another gdb front end - Insight.

Answer 4

For the java programmers out there why not try the Omniscient Debugger? It allows debugging in time (think time-travel) which is very handy.

Answer 5

I wouldn't call it a favorite, but when you need it netcat is quite nice to be able to script network traffic.

Answer 6

printf("%s - %d: %d", __FILE__, __LINE__, variable );
qDebug() << variable;

;-)

Answer 7

printf()

Answer 8

As a C lover I like gdb.

Answer 9

I'll join the C crowd:

gdb, valgrind, gprof.

Edit: I'll join the Java crowd out there as well.

Eclipse debugging tools, firebug,

Answer 10

Firebug for anything related to the web and Eclipse Debugger for stepping through java code. jUnit and Mockito are probably used most in my daily work, though not limited to debugging.

Answer 11

LLVM Clang Static Analysis. It's sweet.

Answer 12

python logging module.

firebug.

liveHTTP headers in firefox.

Safari webinspector.

When it comes to debugging web applications I never use stuff that adds debugging/logging info to the server's output.

I also have my own wsgi middleware I use for debugging web apps. It dumps whole http responses in a database so It can be accessed numerous times. It can be configured to just dump stuff with 500 status code etc. This way I don't have to resend post requests with firebug when I'm debugging ajax stuff, it's also much easier to read this way.

Answer 13

function readVar($var)
{
    echo '<pre>';
    var_dump($var);
    echo '</pre>';
}

I use this about one hundred times a day.

On the client side, it's Firebug, or the primal classic:

<script>
alert('hello1');
.......//borked code stops execution here?
alert('hello2');
.......//hmmm we shall see
</script>

:)

Answer 14

VisualVM might not be the most powerful tool in the Java-world, but it's got a very nice ease-of-use-to-power ratio.