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DAE-AN012: Accessing USB Relay Boards without Sudo in Linux

On Linux, our Java software may requires superuser privileges to communicate with your USB drivers. You can give the desired software superuser priveleges with the sudo command, like this:

sudo java -jar denkovi_software

...but sudo prompts the user for the root password. Suppose you want to allow a user to run the software without a root password, or you just don't want to type sudo each time you run the software. This guide will demonstrate how to configure Ubuntu Linux to allow a particular user to run the desired software for a device without sudo.



Step 1: Add the User to the plugdev Group

Determine if the user is part of the plugdev group with the groups command. Open a terminal window and type:


...replacing USERNAME with the name of the user account. The groups command will print a list of all of the user's groups. Look for the group plugdev. If the user is not already a member of plugdev, add the user with the adduser command:

sudo useradd -G plugdev USERNAME

Run groups USERNAME again to verify that the user is now part of plugdev.



Step 2: Determine your Device's Vendor ID and Product ID

For example the vendor ID and product ID for the USB 4 Relay Board v2 are as follows:

idVendor = 04D8
idProduct = 00DF

For any other device, plug it in, then use the lsusb command to retrieve your hardware's vendor ID and product ID. You will need them below.



Step 3: Add the Device to udev

Now you need to add your hardware to the plugdev group. In the terminal window, navigate to /etc/udev/rules.d and list the contents of the directory.

cd /etc/udev/rules.d

In a fresh installation of Ubuntu 10.04 you should see two files listed: 70-persistent-cd.rules and 70-persistent-net.rules. If you see other files, proceed with caution. If in doubt contact your system administrator. If you are ready to proceed, create a new file in the gedit text editor.

sudo gedit 10-my-usb.rules

You can name this file whatever you want, so long as it ends in ".rules". However, rules files by convention begin with a number. Linux parses rules files in lexical order, and the number makes it easy to see which files will be parsed first. Choosing a low number (like 10, as above) means that your file will be parsed before system rules files.

Add the following text to the file, replacing VENDOR_ID and PRODUCT_ID with the values you found in Step 2 above.

ATTRS{idProduct}=="[VENDOR_ID]", ATTRS{idVendor}=="[PRODUCT ID]", MODE="666", GROUP="plugdev"

For the USB 4 Relay Board v2, the text should look like this:

ATTRS{idProduct}=="00DF", ATTRS{idVendor}=="04D8", MODE="666", GROUP="plugdev"

On older Ubuntu installations you may need to use SYSFS instead of ATTRS, like this:

SYSFS{idProduct}=="00DF", SYSFS{idVendor}=="04D8", MODE="666", GROUP="plugdev"

Save the file and close it. Now tell Ubuntu to reload udev rules by entering the following in the terminal window:

sudo udevadm trigger

Any member of the plugdev group should now be able to run java -jar... denkovi software without using sudo.


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