/lib/crda/setregdomain is in crda 1.1.2-1ubuntu2.
This file is owned by root:root, with mode 0o755.
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 18 19 | #!/bin/sh
set -e
REGDOMAIN=
CRDA_CONF=/etc/default/crda
[ -r "$CRDA_CONF" ] && . "$CRDA_CONF"
[ -z "$REGDOMAIN" ] && exit 0
# In the future, iw may be moved to / filesystem
[ -x /sbin/iw ] && exec /sbin/iw reg set "$REGDOMAIN"
# Wait for /usr, it may not be mounted yet
(
. /lib/udev/hotplug.functions
wait_for_file /usr/sbin/iw
exec /usr/sbin/iw reg set "$REGDOMAIN"
) &
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