I get this error from the rpi_ws281x library when trying to run as user pi (this is a java wrapper around the library):

16:43:59.060 [main] INFO  com.github.mbelling.ws281x.Ws281xLedStrip - LEDs count: 1, GPIO pin: 18, freq hZ: 800000, DMA: 10, brightness: 255, pwm channel: 0, invert: false, strip type: WS2811_STRIP_GRB, clear on exit: true
16:43:59.142 [main] INFO  com.github.mbelling.ws281x.Ws281xLedStrip - Native library loaded
Can't open /dev/mem: Permission denied
!! Failed to initialize WS2811:
java.lang.RuntimeException: Failed to setup lights driver, result code: WS2811_ERROR_MMAP
    at com.github.mbelling.ws281x.Ws281xLedStrip.init(Ws281xLedStrip.java:234)
    at com.github.mbelling.ws281x.Ws281xLedStrip.<init>(Ws281xLedStrip.java:98)

I already followed all possible steps from here, like setting the permissions of /dev/mem and adding user to group gpio, reboot etc. No success. The problem persists. I cannot run my application as super user, as it would screw up a lot of file access and caches I am writing. I really need to be able to run the WS2811 library as a normal user.

  • I'm not sure what you are asking. The library needs root permissions to run.
    – joan
    Jun 18, 2021 at 16:28
  • I am asking for a way to give pi the required permissions, so I can run the process as pi and not super-user
    – 0__
    Jun 19, 2021 at 6:10
  • That becomes a standard permissions problem, i.e. not Pi specific.
    – joan
    Jun 19, 2021 at 7:43
  • That's a Pi specific problem because it is about using a common library for WS2811 LEDs via the GPIO, and requiring the PWM of GPIO 18, which is related to the permissions issue.
    – 0__
    Jun 19, 2021 at 13:14

1 Answer 1


There seems no way around it. A solution with added latency is to run a separate process on root to control the GPIO, and communicate to it from a user process, e.g. using OSC commands.

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