Application note - Example code for capturing power button event on fitlet2 running Linux

• This application note provides an example of how to capture a power button click event on Linux.
• It has been tested with the below setup:

Device: fitlet2
CPU: Intel(R) Atom(TM) Processor E3950
BIOS: 09/17/2018 American Megatrends Inc. FLT2.0.46.01.00
OS: Debian Buster (testing)
Kernel: 4.16.0-2-amd64
ISO: debian-buster-DI-alpha3-amd64-netinst.iso

fitlet2: required BIOS settings

• Press [Delete] button after power-on to enter BIOS settings
• Set BIOS -> Main -> OS selection to [Linux]

Configure power button event handling

• Login as root user (root password required):

$ su -
Password:

• Ignore power button events handling by systemd, then reboot:

$ sed -i s/".*HandlePowerKey.*"/"HandlePowerKey=ignore"/ /etc/systemd/logind.conf
$ reboot

• Install ACPI related software:

$ apt install acpi-support-base acpid

• Verify acpi events are visible in the system, run acpi_listen command and press power button 2-3 times:

$ acpi_listen
button/power PBTN 00000080 00000000
button/power LNXPWRBN:00 00000080 00000007
button/power PBTN 00000080 00000000
button/power LNXPWRBN:00 00000080 00000008

NOTE #1: current power button handler is /etc/acpi/powerbtn-acpi-support.sh, but it does not work for some reason

NOTE #2: there are 2 events PBTN and LNXPWRBN, we need to handle only one of them, for example PBTN

• Create custom power button event rule:

$ cat > /etc/acpi/events/powerbtn-custom-rule << EOF
event=power (PBTN)
action=/etc/acpi/powerbtn-custom-handler.sh
EOF

• Create custom power button event handler and make it executable:

$ cat > /etc/acpi/powerbtn-custom-handler.sh << EOF
#!/bin/sh
echo  "Hello from PBTN!" > /dev/tty1
EOF

$ chmod +x /etc/acpi/powerbtn-custom-handler.sh

• Restart acpid service to activate the new functionality:

$ service acpid restart

• Press power button shortly, you should see "Hello from PBTN!" on the main console