update systemd

technology/linux/udev.md

@@ -4,6 +4,24 @@ arch-wiki: https://wiki.archlinux.org/title/Udev
 ---
 
 # udev
-#wip
-udev
-udevadm
+
+udev is a userspace system that enables the operating system administrator to register userspace handlers for events. The events received by udev's daemon are mainly generated by the (Linux) kernel in response to physical events relating to peripheral devices. As such, udev's main purpose is to act upon peripheral detection and hot-plugging, including actions that return control to the kernel, e.g., loading kernel modules or device firmware. Another component of this detection is adjusting the permissions of the device to be accessible to non-root users and groups.
+
+## Usage
+Send control commands or test the device manager.
+
+Usage: `udevadm [--help] [--version] [--debug] COMMAND [COMMAND OPTIONS]`
+
+Commands:
+```
+  info          Query sysfs or the udev database
+  trigger       Request events from the kernel
+  settle        Wait for pending udev events
+  control       Control the udev daemon
+  monitor       Listen to kernel and udev events
+  test          Test an event run
+  test-builtin  Test a built-in command
+  verify        Verify udev rules files
+  wait          Wait for device or device symlink
+  lock          Lock a block device
+```