Use Port 502 with Modbus-TCP

General
1

Hi,

i want to run the Modbus Flex Server from the module node-red-contrib-modbus on an Raspberry Pi with Raspbian. But whenever i use the default port 502, Node-Red crashes. I found out that, ports below 1024 can not used without root. Then i found the command setcap 'cap_net_bind_service=+ep' [path to node] to have access without running as root.

But now i tried it but it won't work either. I'm not sure i'm using the correct path.

I'm using setcap 'cap_net_bind_service=+ep' /home/pi/.node-red/node_modules/node-red-contrib-modbus/modbus/modbus-flex-server.js

Maybe someone can tell me what i'm doing wrong or give me a solution.
I searched for a while and can't another way to solve it.

Best Regards
Heino

2

I have not done that but I am sure it will not be the path to the node, it may be the path to the nodejs executable. In which case, on a pi, it may be /usr/bin/node so you could try that.

3

Note that this may be a security risk as it means any nodejs application will have those access rights. Whether that is an issue for you depends on the environment you are running in.

4

Thanks for reply.

I tried the path but it also doesn't work. Do you think there is another way to solve this problem?

5

What error are you getting?

6

fehlernodered

As soon as i change the port to 502 this error come up.

7

Where possible please copy/paste terminal output rather than screenshot. When pasting use the </> button at the top of the forum entry window. Thanks.

Can you copy/paste the setcap command you are using and any output it produces please. Also run the command with -v and show us that too. So netcap -v 'cap_net_....

8

I'm sorry for this.

This ist the command i used:

pi@raspberrypi:~ $ sudo setcap -v CAP_NET_BIND_SERVICE=+eip /usr/bin/node
/usr/bin/node: OK

And this is the output i get from Node-Red:

pi@raspberrypi:~ $ ./node-red
24 Jan 11:31:44 - [info]

Willkommen bei Node-RED!
===================

24 Jan 11:31:44 - [info] Node-RED Version: v1.2.7
24 Jan 11:31:44 - [info] Node.js  Version: v14.15.4
24 Jan 11:31:44 - [info] Linux 5.4.79-v7l+ arm LE
24 Jan 11:31:45 - [info] Paletten-Nodes werden geladen
24 Jan 11:31:48 - [info] Einstellungsdatei: /home/pi/.node-red/settings.js
24 Jan 11:31:48 - [info] Kontextspeicher: 'default' [ module=memory]
24 Jan 11:31:48 - [info] Benutzerverzeichnis: /home/pi/.node-red
24 Jan 11:31:48 - [warn] Projekte inaktiviert: editorTheme.projects.enabled=false
24 Jan 11:31:48 - [info] Flow-Datei: /home/pi/.node-red/flows_raspberrypi.json
24 Jan 11:31:48 - [info] Server wird jetzt auf http://127.0.0.1:1880/ ausgefĂĽhrt.
24 Jan 11:31:48 - [info] Flows starten
24 Jan 11:31:48 - [info] Flows gestartet
24 Jan 11:31:48 - [red] Uncaught Exception:
24 Jan 11:31:48 - Error: listen EACCES: permission denied 169.254.231.56:502
    at Server.setupListenHandle [as _listen2] (net.js:1301:21)
    at listenInCluster (net.js:1366:12)
    at doListen (net.js:1503:7)
    at processTicksAndRejections (internal/process/task_queues.js:81:21)
9

Shouldn't the arg be quoted?

sudo setcap 'cap_net_bind_service=+ep' /usr/local/bin/node

(not 100% certain the quotes make any difference)

Also, can you double check the output of which node returns /usr/local/bin/node

11 
sudo setcap -v 'cap_net_bind_service=+ep' /usr/bin/node      /usr/bin/node differs in [i]

sudo setcap -v 'cap_net_bind_service=+ep' /usr/local/bin/node
/usr/local/bin/node differs in [pe]
13

The -v is used to verify that the setcap has worked. Do it without -v first then with to check it.
As suggested, use which node to find where the executable is.

14

Sorry i'm a little confused.

pi@raspberrypi:~ $ which node
/home/pi/.nvm/versions/node/v14.15.4/bin/node

Should i now use this path for the command?
sudo setcap 'cap_net_bind_service=+ep' /home/pi/.nvm/versions/node/v14.15.4/bin/node and then sudo setcap -v 'cap_net_bind_service=+ep' /home/pi/.nvm/versions/node/v14.15.4/bin/node ?

15

So am I, why are you using nvm (node version manager)? I guess you didn't use the recommended method of installing node-red and nodejs on a pi.
Unless you have a good reason I suggest removing the nvm s/w, remove the .nvm folder and run the install script. That will ensure you have a consistent set of tools.
Then use which node again to check that is it using /usr/bin/node and run setcap again with that path.

16

Node-Red was already preinstalled i think. After that i used the recommended method with the install script.

But thanks i try to delete the nvm and run the script again.

17

You probably need to uninstall nvm, not just delete the folder.

18

I tried to remove the npm and installed node-red with the script. Now i think i get the correct path.

pi@raspberrypi:~ $ which node
/usr/bin/node

Then i used the setcap again and now it finally worked.

Thank you a lot.

1 Like
19

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