How to reload udev rules without reboot?

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 most of the time 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.

However, beware that different versions of udev have historically had different triggers for reloading the rules automatically. So if in doubt, call udevadm control --reload-rules: it won’t do any harm anyway.

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'.

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
4. re-trigger with udevadm trigger --attr-match=subsystem=net
5. bring the network interfaces up.

I was surprised how well this worked.

I am not sure if this applies, and this is definitely an older post but it came up pretty high my web search for udev info so I thought I might share some knowledge.

You can trigger udev rules manually for specific devices. This applies only to redhat-related distros (centos fedora etc etc etc)

Once you make the relevant changes in your rules file (/etc/udev/rules.d/whateveryoucalledyourrules), you can echo change in to the device’s uevent.

echo change > /sys/block/devname/partname1/uevent

This will force a udev rule reading for ONLY this device. Much better, and more targeted in my opinion.

For me, below command sequence has worked as it is desired.

I have done modifications in /etc/udev/rules.d/70-persistent-net.rules to change the eth number and to reload them without rebooting.

/etc/init.d/networking stop
/etc/init.d/udev stop
udevadm control --reload-rules
/etc/init.d/udev start
/etc/init.d/networking start

By following this, It was successfully loaded in run time without rebooting the machine.

Any suggestion or recommendations on this are welcome, as I have discovered this on my own by reading the man pages.

I’m adding the correct answer here because it took me a while to notice it in the comment from @enthusiasticgeek.
All you need to do (assuming you are on the console of the server – clearly this is bad to do if you are ssh’d in!):

1. Get a list of the interface module(s) being used:

cat /etc/udev/rules.d/70-persistent-net.rules | grep "PCI device" | perl -pe 's/.*((w+)).*/$1/g'| uniq

In my case, it’s igb, so it prints just that.

2. type sudo rmmod igb (replace igb with your card driver obtained from step 1.

next, edit /etc/udev/rules.d/70-persistent-net.rules as needed, then load the module again using modprobe igb, again replacing igb with yours.

in case of multiple networks

cat /etc/udev/rules.d/70-persistent-net.rules | grep "PCI device" | awk '{print $NF}'|sed -e 's/(//g' -e 's/)//g'| uniq > /tmp/listnet
rm -rf /etc/udev/rules.d/70-persistent-net.rules 
for i in $(cat /tmp/listnet); do rmmod $i; modprobe $i;done
service network restart
rm -rf /tmp/listnet

This is a slight change from the main answer: sudo seemed to be required for me on both commands.

Anecdotal evidence: doing sudo udevadm trigger took ~2 sec, but doing it withOUT sudo took only ~0.2 sec. So clearly they are not doing the same thing for me. Do this instead:

sudo udevadm control --reload-rules
sudo udevadm trigger

And then lastly (per the 2nd link below), unplug your device and plug it back in.

References:

1. How to reload udev rules without reboot?
2. https://askubuntu.com/questions/1048870/permission-denied-to-non-root-user-for-usb-device/1187646#1187646

See comments under both of the answers above as well.