# "Error: Error: Permission denied, cannot open /dev/ttyUSB0"

**URL:** <https://discourse.nodered.org/t/error-error-permission-denied-cannot-open-dev-ttyusb0/90887>\
**Category:** General\
**Created:** [11 September 2024 13:40 UTC](https://discourse.nodered.org/t/error-error-permission-denied-cannot-open-dev-ttyusb0/90887 "2024-09-11T13:40:13Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Karsten](https://avatars.discourse-cdn.com/v4/letter/k/e47c2d/32.png) [@Karsten](https://discourse.nodered.org/u/Karsten)\
**Post date:** [11 September 2024 13:40 UTC](https://discourse.nodered.org/t/error-error-permission-denied-cannot-open-dev-ttyusb0/90887/1 "2024-09-11T13:40:13Z")

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Hello Community,  
To begin with, I would like to say that I have already read various posts on this topic, but unfortunately they have not led to success.  
I run Node-Red on an OpenSuseLeap 15.4.  
I use the node “Node-red-contrib-Modbus” in connection with USB0 to read out a Modbus slave.  
If I use  
mbpoll -a 1 -b 38400 -s 2 -P none -t 4 -r 102 -c 2 /dev/ttyUSB0  
everything works perfectly.

lsof /dev/ttyUSB0  
shows me that nobody is blocking the interface.

Also executed:  
sudo usermod -a -G dialout root  
sudo usermod -a -G dialout node-red

These are the users of the “dialout” group  
grep '^dialout' /etc/group  
dialout:x:490:root,node-red

These are the rights for /dev/ttyUSB0  
ls -l /dev/ttyUSB0  
crw-rw---- 1 root dialout 188, 0 Sep 11 15:13 /dev/ttyUSB0

All node-red processes are executed by root.  
This is my flow:  
[flows.json](https://discourse.nodered.org/uploads/short-url/7udfhRqXi0NLNTIRpS38L4S4Atz.json) (2.6 KB)

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**Author:** ![marcus-j-davies](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/marcus-j-davies/32/103435_2.png) [@marcus-j-davies](https://discourse.nodered.org/u/marcus-j-davies)\
**Post date:** [11 September 2024 19:49 UTC](https://discourse.nodered.org/t/error-error-permission-denied-cannot-open-dev-ttyusb0/90887/2 "2024-09-11T19:49:41Z")

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I know you have said it’s running as root (not really recommended BTW)

But what do you get when you run **whoami** in an **exec** node. Does it show root?

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**Author:** ![system](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/1X/d073cd938eafa2e558d7c2cd59003b3ef4963033.png) [@system](https://discourse.nodered.org/u/system)\
**Post date:** [10 December 2024 19:50 UTC](https://discourse.nodered.org/t/error-error-permission-denied-cannot-open-dev-ttyusb0/90887/3 "2024-12-10T19:50:22Z")

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