Linux udev Guide

Linux udev Guide

Complete beginner-friendly guide to udev on Linux, covering Arch Linux, CachyOS, and other distributions including device management, udev rules, and hardware configuration.

---

Table of Contents

1. Understanding udev
2. udev Basics
3. udev Rules
4. Creating Rules
5. Common Examples
6. Troubleshooting

---

Understanding udev

What is udev?

udev manages device nodes in /dev.

Functions:

• Device detection: Detects hardware changes
• Device nodes: Creates device files
• Permissions: Sets device permissions
• Naming: Provides consistent device names

Why it matters:

• Hotplug support: Handles USB devices
• Persistent naming: Consistent device names
• Permissions: Control device access

---

udev Basics

Check udev

Verify udev:

# Check udev version
udevadm --version

# Check udev service
systemctl status systemd-udevd

List Devices

View devices:

# List all devices
udevadm info --export-db

# List USB devices
lsusb

# List block devices
lsblk

---

udev Rules

Rule Locations

Rule files:

# System rules
/etc/udev/rules.d/

# User rules (if supported)
~/.config/udev/rules.d/

Rule Syntax

Basic format:

ACTION=="add", SUBSYSTEM=="usb", ATTR{idVendor}=="1234", ATTR{idProduct}=="5678", MODE="0666"

Components:

• ACTION: add, remove, change
• SUBSYSTEM: usb, block, input
• ATTR: Device attributes
• MODE: File permissions

---

Creating Rules

Get Device Info

Find device attributes:

# Get device info
udevadm info -a -n /dev/sdb

# Or by path
udevadm info -a -p /sys/class/block/sdb

Create Rule

Write rule:

# Create rule file
sudo vim /etc/udev/rules.d/99-mydevice.rules

Example rule:

# USB device rule
ACTION=="add", SUBSYSTEM=="usb", ATTR{idVendor}=="1234", ATTR{idProduct}=="5678", MODE="0666", GROUP="users"

---

Common Examples

USB Device Permissions

Allow USB access:

# USB storage
ACTION=="add", SUBSYSTEM=="block", SUBSYSTEMS=="usb", MODE="0666", GROUP="users"

Persistent Device Names

Create symlink:

# Create symlink for USB device
ACTION=="add", SUBSYSTEM=="block", ATTR{serial}=="ABC123", SYMLINK+="myusb"

Run Script on Device

Execute script:

# Run script when device added
ACTION=="add", SUBSYSTEM=="usb", RUN+="/usr/local/bin/my-script.sh"

---

Troubleshooting

Rule Not Working

Test rule:

# Test rule
udevadm test /sys/class/block/sdb

# Reload rules
sudo udevadm control --reload-rules

# Trigger rules
sudo udevadm trigger

Check Device Info

Debug device:

# Get device info
udevadm info -a -n /dev/sdb

# Monitor events
udevadm monitor

---

Summary

This guide covered udev basics, rule creation, and device management for Arch Linux, CachyOS, and other distributions.

---

Next Steps

• Hardware Detection - Hardware setup
• System Configuration - System setup
• udev Documentation: man udev

---

This guide covers Arch Linux, CachyOS, and other Linux distributions. For distribution-specific details, refer to your distribution's documentation.