/etc/acpi/events/sleepbtn is in acpi-support 0.142-6.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 | # /etc/acpi/events/sleepbtn
# Called when the user presses the sleep button
# Note that this script is part of the SUSPEND part of acpi-support. This is
# not a key translation event, it is intended to perform a suspend if no
# power management daemon is running.
event=button[ /]sleep
action=/etc/acpi/sleep_suspend.sh sleep
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