Port 5001 is not open on localhost, could not start Functions Emulator

[REQUIRED] Environment info

npm 6.13.7 node v12.11.1

firebase-tools: 8.4.3

Platform: mac os Catalina 10.15.5

[REQUIRED] Test case

• none

[REQUIRED] Steps to reproduce

firebase init (install firestore and functions) firebase emulators:start

[REQUIRED] Expected behavior

Firestore and Functions emulators should start

[REQUIRED] Actual behavior

Only Firestore starts, Functions emulator fails:

`$ firebase emulators:start --debug
[2020-06-28T17:43:53.149Z] > command requires scopes: ["email","openid","https://www.googleapis.com/auth/cloudplatformprojects.readonly","https://www.googleapis.com/auth/firebase","https://www.googleapis.com/auth/cloud-platform"]
[2020-06-28T17:43:53.150Z] > authorizing via signed-in user
i  emulators: Starting emulators: functions, firestore {"metadata":{"emulator":{"name":"hub"},"message":"Starting emulators: functions, firestore"}}
⚠  hub: emulator hub unable to start on port 4400, starting on 4401 instead. {"metadata":{"emulator":{"name":"hub"},"message":"emulator hub unable to start on port 4400, starting on 4401 instead."}}
[2020-06-28T17:43:53.173Z] [hub] writing locator at /var/folders/c1/vlr0jfwj3rn2rsfnp3ztlyjm0000gn/T/hub-practicelyapp.json
i  emulators: Shutting down emulators. {"metadata":{"emulator":{"name":"hub"},"message":"Shutting down emulators."}}
i  hub: Stopping emulator hub {"metadata":{"emulator":{"name":"hub"},"message":"Stopping emulator hub"}}
⚠  functions: Port 5001 is not open on localhost, could not start Functions Emulator. {"metadata":{"emulator":{"name":"functions"},"message":"Port 5001 is not open on localhost, could not start Functions Emulator."}}
⚠  functions: To select a different host/port, specify that host/port in a firebase.json config file:
      {
        // ...
        "emulators": {
          "functions": {
            "host": "HOST",
            "port": "PORT"
          }
        }
      } {"metadata":{"emulator":{"name":"functions"},"message":"To select a different host/port, specify that host/port in a firebase.json config file:\n      {\n        // ...\n        \"emulators\": {\n          \"functions\": {\n            \"host\": \"\u001b[33mHOST\u001b[39m\",\n            \"port\": \"\u001b[33mPORT\u001b[39m\"\n          }\n        }\n      }"}}
i  emulators: Shutting down emulators. {"metadata":{"emulator":{"name":"hub"},"message":"Shutting down emulators."}}

Error: Could not start Functions Emulator, port taken.`

[samtstern]

@julianiaccopucci the problem and solution are both inside of the error message you posted. Port 5001 is busy on your machine so you need to choose another port. To do this, add an entry in your firebase.json like this:

      {
        // ...
        "emulators": {
          "functions": {
            "port": "PORT"
          }
        }
      }

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