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--- fuss:udev [2017/07/05 19:07] – office
+++ fuss:udev [2019/03/08 22:40] – [Reloading Udev Rules] office
@@ Line 1: / Line 1: @@
+====== Creating Specific Rules for Devices ======
+Usually, rules are placed in files under the ''/etc/udev/rules.d'' directory where each rule performs some action depending on some user-specified criteria that matches a connected devices. For instance, a modem may be connected to a computer and the kernel will assign via udev a device node under ''/dev/'' - however, in most cases, the actual name is chosen by the kernel (conventionally incrementally, depending on the number of already connected devices). Unfortunately, one cannot know beforehand if, following the example, a modem device will be assigned to ''/dev/ttyACM0'' or ''/dev/ttyACM1'', etc...
+To make sure that a device gets the same node under devfs via udev, rules can be added under ''/etc/udev/rules.d'' and those rules can match hardware criteria such as vendor ID, revision, etc... The first step is to issue the command:
+<code bash>
+udevadm info -q all -n /dev/ttyACM0 --attribute-walk
+</code>
+where:
+  * ''/dev/ttyACM0'' is the connected device you want to query for hardware details.
+The command will output attributes, such as ''ATTRS{idProduct}'', ''ATTRS{idVendor}'', etc... Information that can then be used to construct an udev rule.
+For instance, to match and USB device with an ''idProduct'' attribute of ''0723'' and an ''idVendor'' of ''05e3'', one could create a file at ''/etc/udev.d/rules/80-mydevice.rules'' containing:
+<code>
+SUBSYSTEM=="usb",ATTRS{idProduct}=="0723",ATTRS{idVendor}=="05e3",SYMLINK+="mydevice",RUN+="echo boo >/dev/null"
+</code>
+which will:
+  * match a device connected through the USB subsystem,
+  * that has an ''idProduct'' of ''0723'',
+  * and an ''idVendor'' of ''05e3'',
+  * as well as creating a convenient symlink in ''/dev/'' as ''/dev/mydevice'',
+  * and additionally execute the command ''echo boo >/dev/null''
+====== Reloading Udev Rules ======
+Remember that issuing:
+<code bash>
+udevadm control --reload-rules
+</code>
+is insufficient and that you have to issue:
+<code bash>
+systemctl restart udev.service
+</code>
+to make the rules effective.
+====== Trigger Action for Particular Set of Rules ======
+To trigger the ''net'' subsystem rules that bind to the ''add'' action, issue:
+<code bash>
+udevadm trigger --attr-match=subsystem=net --action="add"
+</code>