Solved ACPI, sleep: suspend by default for the power button

I experimented:

$ grep -i acpi /boot/loader.conf

Not effective. I guess, because hw.acpi.power_button_state is a sysctl variable but not a loader tunable; acpi(4).

Is there a way to have the button suspend by default?

Thanks, I wasn't aware of the existence of /etc/sysctl.conf – that's what I needed.

I had not read lid-related topic 6942 because the notebook is sometimes used in clamshell mode.

(OT: wake from sleep is reliable. Sleep is not reliable; I'll pursue this elsewhere.)