postinst is in hdparm 9.37-0ubuntu3.
This file is a maintainer script. It is executed when installing (*inst) or removing (*rm) the package.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | #!/bin/sh
set -e
if [ -n "$2" ] && dpkg --compare-versions "$2" lt 8.9-2; then
  rm -fv /etc/rc0.d/K75hdparm /etc/rc6.d/K75hdparm
fi
# Automatically added by dh_installudev
if [ "$1" = configure ]; then
	if [ -e "/etc/udev/rules.d/85_hdparm.rules" ]; then
		echo "Preserving user changes to /etc/udev/rules.d/85-hdparm.rules ..."
		if [ -e "/etc/udev/rules.d/85-hdparm.rules" ]; then
			mv -f "/etc/udev/rules.d/85-hdparm.rules" "/etc/udev/rules.d/85-hdparm.rules.dpkg-new"
		fi
		mv -f "/etc/udev/rules.d/85_hdparm.rules" "/etc/udev/rules.d/85-hdparm.rules"
	fi
fi
# End automatically added section
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