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How should one reload udev rules, so that newly created one can function?

I'm running Arch Linux, and I don't have a udevstart command here.

Also checked /etc/rc.d, no udev service there.

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4 Answers 4

up vote 41 down vote accepted
# udevadm control --reload-rules
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Do you need udevtrigger afterwards? –  Nils May 26 '12 at 20:28
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@Nils Actually, you may need udevtrigger (or rather udevadm trigger on most distributions) instead (that, or plug the device out and back it). --reload-rules is almost always useless as it happens automatically. –  Gilles Mar 5 '13 at 10:28
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udevadm trigger did the trick on CentOS 6 for me. –  astrostl Aug 7 '13 at 18:19

Udev uses the inotify mechanism to watch for changes in the rules directory, in both the library and in the local configuration trees (typically located at /lib/udev/rules.d and /etc/udev/rules.d). So you don't need to do anything when you change a rules file.

You only need to notify the udev daemon explicitly if you're doing something unusual, for example if you have a rule that includes files in another directory. Then you can use the usual convention for asking daemons to reload their configuration: send a SIGHUP (pkill -HUP udevd). Or you can use the udevadm command: udevadm control --reload-rules.

The udev rules are only applied when a device is added. If you want to reapply the rules to a device that is already connected, you need to do this explicitly, by calling udevadm trigger with the right options to match the device(s) whose configuration has changed, e.g. udevadm trigger --attr-match=vendor='Yoyodyne' --attr-match=model='Frobnicator 300'.

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+1 for the Pynchon reference :) –  jasonwryan Oct 20 '12 at 20:50
    
+1 for the hint about reconnecting the device. facepalm –  Raphael Dec 5 '12 at 21:12

Please note that more recent versions of udev have dropped the inotify support so the reloading of the rules on change is needed more often these days.

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Can you show a reference/git commit? –  drahnr Jan 6 at 9:14

I'm adding this because some day I will need it... again.

Sometimes you get an incorrect matching of ethernet device numbers and MAC addresses. Sometimes this is really important, like when running in a VM and each device is assigned to a different VLAN.

  1. Bring the network interfaces down, then
  2. modify /etc/udev/rules.d/70-persistent-net.rules (or its equivalent)
  3. re-load with udevadm control --reload-rules and finally
  4. re-trigger with udevadm trigger --attr-match=subsystem=net
  5. bring the network interfaces up.

I was surprised how well this worked.

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