# modbusRTU over RS485: Port Not Option
**URL:** https://discourse.nodered.org/t/modbusrtu-over-rs485-port-not-option/77204
**Category:** General
**Created:** [3 April 2023 15:12 UTC](https://discourse.nodered.org/t/modbusrtu-over-rs485-port-not-option/77204 "2023-04-03T15:12:48Z")
**Posts on this page:** 9
**Page:** 1
### Author:  [@hobbes1069](https://discourse.nodered.org/u/hobbes1069)
#### Post date: [3 April 2023 15:12 UTC](https://discourse.nodered.org/t/modbusrtu-over-rs485-port-not-option/77204/1 "2023-04-03T15:12:48Z")
This seems to be a re-occurring problem with these nodes and reading through several of the topics (including my previous [one](https://discourse.nodered.org/t/modbus-tcp-inconsistencies-issues/64032)).
This time I'm trying to connect to a serial device. It was working on a Tulip Edge IO device using their ancient Node Red 1.3.5. At some point `node-red-contrib-modus` was updated to no longer be compatible with 1.X so I put Fedora Linux on a tablet and installed Node Red 3.0.2 (and the latest `node-red-contrib-modbus`).
Using a catch node I can get the following very unhelpful error:
```auto
Error: Port Not Open
at /home/nodered/.node-red/node_modules/node-red-contrib-modbus/modbus/maps/core/core/modbus-client-core.js:79:156
```
Looking at line 79 of the file on github seems to be for closing the port. So am I to assume it's trying to close a port that's not open?
Furthermore, the documentation for `node-red-contrib-modbus` is very confusing. At the top it says it's BASED on `modbus-serial`, but in the details says to test using `modbus-serial` if you have issues.
Which I did with what I think is success. I don't have the controller I'm trying to talk to while I'm troubleshooting in the lab but I can see the TX light blink on the USB-\>RS485 adapter when I run the following script and do not see a blink when I click the inject node in NR.
```auto
$ cat modbus-test.js
const ModbusRTU = require('modbus-serial');
const client = new ModbusRTU();
client.connectRTUBuffered('/dev/ttyUSB0', { baudRate: 19200 }, (err) => {
if (err) {
console.error(err);
return;
}
client.setID(1); // Modbus slave address
client.setTimeout(500);
const start = 2000; // starting register address
const quantity = 10; // number of registers to read
client.readHoldingRegisters(start, quantity)
.then((data) => {
console.log(data); // do something with the received data
})
.catch((err) => {
console.error(err); // handle error
})
.finally(() => {
client.close(); // close connection after the operation is complete
});
});
```
For posterity here's the flow:
---
### Author:  [@hobbes1069](https://discourse.nodered.org/u/hobbes1069)
#### Post date: [3 April 2023 17:32 UTC](https://discourse.nodered.org/t/modbusrtu-over-rs485-port-not-option/77204/2 "2023-04-03T17:32:12Z")
🤬 🤬 🤬
I had COMPLETELY FORGOTTEN that by default the installer creates a `nodered` user rather than install as the current user.
Added `nodered` to the `dialout` group and now it can open the port!
---
### Author:  [@Colin](https://discourse.nodered.org/u/Colin)
#### Post date: [3 April 2023 18:56 UTC](https://discourse.nodered.org/t/modbusrtu-over-rs485-port-not-option/77204/3 "2023-04-03T18:56:43Z")
> [@hobbes1069](#):
>
> the installer creates a `nodered` user
Which installer is that?
---
### Author:  [@hobbes1069](https://discourse.nodered.org/u/hobbes1069)
#### Post date: [3 April 2023 19:22 UTC](https://discourse.nodered.org/t/modbusrtu-over-rs485-port-not-option/77204/4 "2023-04-03T19:22:52Z")
> **[GitHub - node-red/linux-installers: Node-RED install scripts for various...](https://github.com/node-red/linux-installers)**
>
> Node-RED install scripts for various flavours of Linux - GitHub - node-red/linux-installers: Node-RED install scripts for various flavours of Linux
---
### Author:  [@Colin](https://discourse.nodered.org/u/Colin)
#### Post date: [3 April 2023 20:02 UTC](https://discourse.nodered.org/t/modbusrtu-over-rs485-port-not-option/77204/5 "2023-04-03T20:02:44Z")
Which one of those?
---
### Author:  [@hobbes1069](https://discourse.nodered.org/u/hobbes1069)
#### Post date: [3 April 2023 20:16 UTC](https://discourse.nodered.org/t/modbusrtu-over-rs485-port-not-option/77204/6 "2023-04-03T20:16:13Z")
Sorry, had to be quick as I had a meeting to get to...
The RPM method (Since it's Fedora Linux).
Looks like it's related to this commit:
>
>
> \- \[x\] install for another user by setting environment variable e.g. \`NODERED\_USE…R=test\`
> \- \[x\] suggest user \`nodered\` during install when environment variable \`NODERED\_USER\` is not set.
> \- \[x\] comment low memory NODE OPTIONS
> \- \[x\] correct environmentFile, to /etc/node-red/environment
> \- \[x\] add some color to differentiate users
> \- \[x\] can be started as root or normal user, will prompt for password for sudo
It changed a little over a year ago but I haven't used it on a fresh install in a while.
---
### Author:  [@Colin](https://discourse.nodered.org/u/Colin)
#### Post date: [3 April 2023 20:30 UTC](https://discourse.nodered.org/t/modbusrtu-over-rs485-port-not-option/77204/7 "2023-04-03T20:30:41Z")
OK, that appears to be specific to the rpm version. I wonder why that was done.
---
### Author:  [@hobbes1069](https://discourse.nodered.org/u/hobbes1069)
#### Post date: [18 April 2023 23:24 UTC](https://discourse.nodered.org/t/modbusrtu-over-rs485-port-not-option/77204/8 "2023-04-18T23:24:24Z")
I don't think it's necessarily a bad idea. Flowforge does the same thing, but some reminders about WHO needs to be in the dialout group would be good. 🙂
---
### Author:  [@system](https://discourse.nodered.org/u/system)
#### Post date: [9 May 2023 14:35 UTC](https://discourse.nodered.org/t/modbusrtu-over-rs485-port-not-option/77204/10 "2023-05-09T14:35:30Z")
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