"Permission denied" when try to copy file to usb

General
1

I'am working on raspberry device and i have to copy a file to my usb connected.
Sometimes, it works but sometimes, i get error on copy node and i get "permission denied".
I wonder what causes this problem to appear suddenly then it despears ?
And how can i avoid this type of error ? Do i need each time to use "chmod" to change permission on files ??

2

So this is one possible scenario that may be happening. Happened to me.
So lets say your allowed to read or write to USB-Drive.
You write a file with node-red to the USB-Drive
then you take that USB-Drive and plug it in another computer and read and write to that file.
When you plug it back into the node-red computer and try to read and write to it you get "permission denied"

I had the above happen. Started setting my user:group permission for the file every time I did something to it on another computer. especially if i created a new file.

open the folder in terminal where the file is located.

$ chown nodered:nodered ./name_of_your_file.txt
$ chmod 755 ./name_of_your_file.txt

755 I can change and run it, everyone else can run it.
644 I can change it, everyone else can read it.

good luck!

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3

Are you possibly sometimes using sudo when running something that writes to the file? Either running a command or starting node-red for example. If you do that then afterwards you won't be able to write to the file without using sudo or changing the permissions.

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4

How is the usb drive mounted to the raspberry pi, and with what permissions? That might be related too