How do I tell whether a device is plugged into the headphone jack? acpid can: every time I plug a device into it /var/log/messages notes, 'logger: ACPI group jack / action headphone is not defined'

The mixer in my distribution shows this info.

What mixer is that? amixer, alsamixer, rexima don't.

I am using pulse audio.

I know in the past it was buggy and had problems. It has not given me any issues for the last couple years.

I originally assumed you were asking "How do you detect this via Linux files" or via a program, and not just via Desktop widgets. But in poking around my system, I couldn't find that response easily. Turns out a bit of googling immediately helped, and peeps to this stack exchange question/answer.

If you were interested in via a program or a system file, check out /proc/acound/card0/codec#0. What I did was concatenated that to a file in my home directory with no headphones inserted and a different file in my home directory after plugging in headphones and then compared the two files.

Obviously ALSA knows you did this action, and if you need to go deeper about how things are understood, then you'd have to grab the ALSA sources and determine where these changes are detected. My assumption is that it comes from the BIOS.

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Thanks. I had already checked this, but I looked too quickly: it takes a few seconds for this file to reveal a change in plugged-in-ness.