http://www.thelinuxwiki.com/index.php?action=history&feed=atom&title=Udev_rulesUdev rules - Revision history2026-04-29T00:15:55ZRevision history for this page on the wikiMediaWiki 1.21.5http://www.thelinuxwiki.com/index.php?title=Udev_rules&diff=331&oldid=prevNighthawk: Pushed from Themanclub.2013-05-17T18:20:49Z<p>Pushed from Themanclub.</p>
<p><b>New page</b></p><div>udev rules are flexible and very powerful. Here are some of the things you can use rules to achieve:<br />
<br />
*Rename a device node from the default name to something else<br />
*Provide an alternative/persistent name for a device node by creating a '''symbolic link''' to the default device node<br />
*Name a device node based on the output of a program<br />
*Change permissions and ownership of a device node<br />
*Launch a script when a device node is created or deleted (typically when a device is attached or unplugged)<br />
*Rename network interfaces<br />
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== rules dir ==<br />
<br />
/etc/udev/rules.d/<br />
<br />
<br />
== rules file name==<br />
(to be parsed before default rules)<br />
10-local.rules<br />
<br />
<br />
== Gathering device info ==<br />
example for /dev/sdc<br />
udevadm info -a -p $(udevadm info -q path -n /dev/sdc)|grep -E "device|parent|KERNEL|SUBSYSTEMS|model"<br />
<br />
== example rules ==<br />
<br />
usb hard drive<br />
KERNEL=="sd*", SUBSYSTEMS=="scsi", ATTRS{model}=="External USB HDD", SYMLINK+="usbhd%n"<br />
<br />
== testing the rules ==<br />
<br />
Assuming you are on a recent kernel with inotify support, udev will automatically monitor your rules directory and automatically pick up any modifications you make to the rule files. <br />
<br />
to check you kernel...<br />
'''# cat /etc/kernkels/kernel-name |grep INOTIFY'''<br />
CONFIG_INOTIFY_USER=y<br />
<br />
To test with inotify support... first we must make the rules take effect<br />
<br />
If the device is removable, then disconnect and reconnect <br />
<br />
or<br />
<br />
if non-removable you can run <br />
'''# udevadm trigger'''<br />
<br />
if your kernel does not have inotify support, new rules will not be detected automatically. In this situation, you must run<br />
'''# udevadm control --reload-rules'''<br />
<br />
Next we can view the symbolic links get created dymically<br />
<br />
Example with cellphone plugged first, ext usb HD plugged in second...<br />
'''# ls /dev/sd*'''<br />
/dev/sda /dev/sda2 /dev/sda5 /dev/sdb1 /dev/sdc /dev/sdd1<br />
/dev/sda1 /dev/sda4 /dev/sdb /dev/sdb2 /dev/sdd /dev/sdd2<br />
<br />
<br />
# '''ls -l /dev/usbh*'''<br />
lrwxrwxrwx 1 root root 3 Jan 25 23:44 /dev/usbhd -> sdd<br />
lrwxrwxrwx 1 root root 4 Jan 25 23:44 /dev/usbhd1 -> sdd1<br />
lrwxrwxrwx 1 root root 4 Jan 25 23:44 /dev/usbhd2 -> sdd2<br />
<br />
unplugged both devices, then plugged in usb HD , note the symlinks correctly point to the new device labels<br />
<br />
'''# ls -l /dev/usbh*'''<br />
lrwxrwxrwx 1 root root 3 Jan 25 23:49 /dev/usbhd -> sdc<br />
lrwxrwxrwx 1 root root 4 Jan 25 23:49 /dev/usbhd1 -> sdc1<br />
lrwxrwxrwx 1 root root 4 Jan 25 23:49 /dev/usbhd2 -> sdc2<br />
<br />
<br />
<br />
Links:<br />
http://www.gentoo.org/doc/en/udev-guide.xml<br />
http://www.reactivated.net/writing_udev_rules.html#example-usbhdd<br />
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<br />
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[[category:linux]]</div>Nighthawk