NOTE: this page is for archival only, see the note at the end of the page.

Central Regulatory Domain Agent

CRDA acts as the udev helper for communication between the kernel and userspace for regulatory compliance. It relies on nl80211 for communication.


You can get the latest CRDA code from:



You can get CRDA releases here

Usage design in Linux

For details please see mac80211 802.11d support and cfg80211 regulatory support sections.

Letting the kernel call CRDA

We use userspace events (uevents) to let he kernel speak to userspace. Below is an example udev rule you can place into your distribution's udev rules directory (usually /etc/udev/rules.d/). Note that most distributions have udev configured with inotify on the udev rules directory, so there is no need to restart udev after adding the new rule.

# Example file, should be put in /etc/udev/rules.d/regulatory.rules
KERNEL=="regulatory*", ACTION=="change", SUBSYSTEM=="platform", RUN+="/sbin/crda"

Debugging kernel to CRDA communication

To debug communication between the kernel and udev you can monitor udev events:

udevadm monitor --environment kernel


CRDA is licensed under the ISC license in hopes other operating systems can benefit from a community project to enhance regulatory considerations.

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