write and debug udev rules by simulating device events with udevadm test before relying on real hardware hotplug
domain: freedesktop.org · 5 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗
Steps
Identify the sysfs device path to target with `udevadm info -q path -n /dev/<device>` or by browsing /sys/devices.
Simulate an event against that path without physically unplugging/replugging the device: `udevadm test --action=add /sys/devices/.../<device>`.
Iterate on the rule file in a scratch directory and load it for testing without installing it system-wide using `udevadm test --extra-rules-dir=<dir> ...`.
Increase verbosity of the rule-matching trace with -v/--verbose to see exactly which rule lines matched or were skipped.
Once the simulated run looks correct, install the rule into /etc/udev/rules.d/ and reload the running daemon's rules with `udevadm control --reload`.
Known gotchas
`udevadm test` is explicitly documented as debug-only; it does not execute any RUN{program} actions, so a rule that 'passes' the test can still fail at the RUN step in a real event.
Some property values available during a real hotplug event may differ or be unavailable during a simulated run, so a successful test isn't a full guarantee of identical behavior on real hardware.
Rules placed in /etc/udev/rules.d/ can be overridden by higher-priority rules already shipped in /usr/lib/udev/rules.d/; testing a rule in isolation with --extra-rules-dir won't reveal these ordering conflicts.
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