Node.js: How to attach to a running process and to debug the server with a console?
I use 'forever' to run my application. I want to attach to the running environment to inspect my application. So what can I do?
From http://nodejs.org/api/debugger.html:
Advanced Usage
The V8 debugger can be enabled and accessed either by starting Node with the --debug command-line flag or by signaling an existing Node process with SIGUSR1.
Find the PID of your node process and then sending SIGUSR1 should do the trick:
kill -s SIGUSR1 nodejs-pid
Then run node-inspector and browse to the URL it indicates. More in this tutorial.
You can add a REPL to your app. For example, if you add a REPL to listen on localhost port 5001, you start your app as usual and login with telnet: telnet localhost 5001 . That will take you to a prompt where you can interact with your app directly.
Alternatively, if you need to your app to "pause" when it reaches a certain state, you need to add "debugger;" lines to areas of your code where you want those breakpoints, then start the app in debug mode.
Hope that helps.
Starting from Node 6.3 , node has a built-in debugger that can be triggered (even in a production app) by doing:
kill -USR1 <node-pid>
The node process will spit out something like this:
Debugger listening on ws://127.0.0.1:9229/f3f6f226-7dbc-4009-95fa-d516ba132fbd
For help see https://nodejs.org/en/docs/inspector
chrome://inspect on http://host.domain:9229 . If you cannot connect via a browser (ie the server is in a firewalled production cluster), you can activate a REPL to inspect over the command line:
node inspect -p <node-pid>
Prior to this version, node-inspector was a separate tool for debugging Node processes. However, as documented on its own page, it is mostly deprecated as the now-bundled debugger is actively maintained and provides more advanced features. For more information on this change, see this thread.
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