firebase serve: supervisorPort (5001) is already in use - firebase

Question

I built this React App, that allows users to add todo item, and mark an item as completed/active. Todo items are stored in cloud firestore.
I want to enable full-text search on the app, and one way is to create a cloud function that writes index to Algolia whenever cloud firestore witnesses a create operation.
Inside my app root directory, I initialize cloud functions and then implement the onTodoAdded function. After done, I run firebase serve under functions directory and get the errors:
=== Serving from '/Users/evan/source/react-redux-todos'...
i functions: Preparing to emulate functions.
Warning: You're using Node.js v10.6.0 but Google Cloud Functions only supports v6.11.5.
i hosting: Serving hosting files from: build
✔ hosting: Local server: http://localhost:5000
error: SUPERVISOR error Error: listen EADDRINUSE 127.0.0.1:5001
at Server.setupListenHandle [as _listen2] (net.js:1335:14)
at listenInCluster (net.js:1383:12)
at GetAddrInfoReqWrap.doListen [as callback] (net.js:1509:7)
at GetAddrInfoReqWrap.onlookup [as oncomplete] (dns.js:61:10)
error: supervisorPort (5001) is already in use
i functions: No HTTPS functions found. Use firebase functions:shell if you would like to emulate other types of functions.
For a complete debug log, find here.
However, this command works fine: firebase serve --only functions.
=== Serving from '/Users/evan/source/react-redux-todos'...
i functions: Preparing to emulate functions.
Warning: You're using Node.js v10.6.0 but Google Cloud Functions only supports v6.11.5.
i functions: No HTTPS functions found. Use firebase functions:shell if you would like to emulate other types of functions.
Since it says supervisorPort(5001) is already in use, I lsof -i:5001 and finds no process. I also shut down my laptop and restart, gets the same error.
I find the similar issue here, however didn't find the solution.

Answer 1

I still don't know the reason, but adding --port=9000 solves the problem. For example, firebase serve --only functions --port=9000. Credits to restPort (5001) is already in use #142.

Answer 2

I was having this same error after updating to macOS Mojave 10.14.1 (was fine with 10.14). error: supervisorPort (5001) is already in use and it led me down this rabbit hole of additional updates and configuration that eventually got it to work.
1 Update Node Packages
I updated these items to these versions (latest as of this writing)
firebase-functions: 2.1.0
firebase: 5.5.8
I deleted by node_modules folder and reinstalled all the packages.
2 Firestore Emulator Setup Required
Next time I attempted to serve, firebase gave me this error:
Setup required, please run: firebase setup:emulators:firestore
Because of the weird permissions issues I initially had with mac, I actually have to run
node_modules/.bin/firebase setup:emulators:firestore
3 Then.... Fix Java Runtime Issues
On my next serve attempt, I was presented with firestore: No Java runtime present, requesting install. Mac presents a popup leading to a page where you can "download java for mac". This isn't what you actually need. You really need the Java SE Development Kit which enables command line interface.
Then... You may get these errors the next time you try to serve.
error: restPort (5002) is already in use
error: SUPERVISOR error Error: listen EADDRINUSE 127.0.0.1:5001
at Object._errnoException (util.js:1022:11)
at _exceptionWithHostPort (util.js:1044:20)
at Server.setupListenHandle [as _listen2] (net.js:1351:14)
at listenInCluster (net.js:1392:12)
at GetAddrInfoReqWrap.doListen [as callback] (net.js:1501:7)
at GetAddrInfoReqWrap.onlookup [as oncomplete] (dns.js:97:10)
error: supervisorPort (5001) is already in use
But Firebase still ended up continuing to successfully serve somehow, despite these errors. And it still shows my app over http://localhost:5000.
Hope this helps!