Error opening serial port /dev/ttyACM0: Port not found

[budryerson]

I'm running a fresh install of Ubuntu 25.04 on a RaspberryPi4B with Processing 4.4.4. I cannot get the serial ports to work. Here is a simple sketch:

import processing.serial.*;
Serial myPort;

void setup()
{
 println(Serial.list());
 String portName = Serial.list()[0];
 println(portName);
 myPort = new Serial(this, portName, 9600);
}

void draw()
{
}

Serial.list() appears to work correctly.
Console output:

/dev/ttyACM0
/dev/ttyACM0

I also get the red banner error code:
Error opening serial port /dev/ttyACM0: Port not found

I thought it might have something to do with permissions:

$ ls -l /dev/ttyACM0
crw-rw-rw- 1 root dialout 166, 0 May 24 11:52 /dev/ttyACM0

I am in both the dialout and the tty group.

$ groups budryerson
budryerson : budryerson adm tty dialout cdrom sudo dip plugdev users lpadmin

I've been beating my head against this for days, and I'm not getting anywhere. I turn to you, my friends, for help. Does anybody have any ideas?

Thanks,
Bud Ryerson
San Francisco

[EthanPal]

I have the same problem on Raspberry Pi (Raspberry Pi OS) and Ubuntu, seems a problem on Linux system.
The problem is exactly the same, I tried various methods but couldn't get a solution.
Need help!

[SableRaf]

Hi @budryerson @EthanPal ,

This issue happens because the current Linux install restricts access to certain system resources for security reasons; but in this case, it's a bit too strict.

As a workaround, you can use the portable version from the 4.4.4 release on GitHub. That should allow access to /dev/ttyACM0 without any issues.

We're working on a better out-of-the-box experience on Linux. Thanks for your patience while we sort this out.