Introduction

This article describes the workflow about udev daemon.

Table of Contents

Workflow

major, minor number of device may change depends on order of detection.

sd<letter(s)><optional number(s)>

SCSI controller (host bus adapter or HBA)

HBA moves to another slot

Fibre channel /etc/fstab file

WWID:world wide ID

        event        |- udev rules
kernel ------> udev <|
                     |- action

Problems

  • may not be accessible at the time
  • event anytime
  • delay
  • blkid extends access problems

Udev Device Manager

----------------
| /sys -> attr | -> udev -> make dev nodes
----------------

Persistent Device Names

/etc/udev/udev.conf

  • udev_log
  • udev_root (deffault: /dev)

Insepct Deivce Info

udevadm info {--attribute-walk} --query={path,all,env,property} --name=/dev/sda

Test Configuration

udevadm test /sys/class/block/sda

Restart udev Daemon

systemctl restart systemd-udevd.service

Inspect network interface card information

Udevadm info starts with the device specified by the devpath and then walks up the chain of parent devices. It prints for every device found, all possible attributes in the udev rules key format. A rule to match, can be composed by the attributes of the device and the attributes from one single parent device.

udevadm info -p /sys/class/net/eno0  -a

References