On my new laptop, I have an error in dmesg which occurs every 2 seconds:

acpi PNP0501:00: Still not present

What does this mean? How to troubleshoot it?

1 Answer 1


TL;DR: The message means that the ACPI tables in the BIOS are buggy. A BIOS update may help.

PNP0501 is the Plug&Play code for "16550A-compatible COM port". :00 means the first device of this kind, as found in the ACPI DSDT table.

The error message Still not present means that the BIOS informed the OS that the status of the device changed, but when trying to configure it, the kernel noticed that it still isn't available.

In short

acpi PNP0501:00: Still not present

roughly translates to

"ACPI said there is a COM port on this mainboard, and it said that its status changed, so as it wasn't available before, it should be available by now, but it isn't."

It's a harmless warning, but further troubleshooting might be possible by using the Linux ACPI debugging facility and DSDT overriding or method customizing.

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