ABOUT UDEV
udev - Linux dynamic device management udev (userspace /dev) is a device manager for the Linux kernel
CONFIG FILE RELATED
# do not edit this file, it will be overwritten on update
ACTION=="remove", GOTO="cdrom_end"
SUBSYSTEM!="block", GOTO="cdrom_end"
KERNEL!="sr[0-9]*|xvd*", GOTO="cdrom_end"
ENV{DEVTYPE}!="disk", GOTO="cdrom_end"
# unconditionally tag device as CDROM
KERNEL=="sr[0-9]*", ENV{ID_CDROM}="1"
# media eject button pressed
ENV{DISK_EJECT_REQUEST}=="?*", RUN+="cdrom_id --eject-media $tempnode", GOTO="cdrom_end"
# import device and media properties and lock tray to
# enable the receiving of media eject button events
IMPORT{program}="cdrom_id --lock-media $tempnode"
LABEL="cdrom_end"
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"/lib/udev/rules.d/60-cdrom_id.rules" [readonly] 18L, 584C 1,3 All
RELATED SHELL SESSION (cdrom)
[bash]
$cat /proc/sys/dev/cdrom/info
CD-ROM information, Id: cdrom.c 3.20 2003/12/17
drive name: sr0
drive speed: 48
drive # of slots: 1
Can close tray: 1
Can open tray: 1
Can lock tray: 1
Can change speed: 1
Can select disk: 0
Can read multisession: 1
Can read MCN: 1
Reports media changed: 1
Can play audio: 1
Can write CD-R: 1
Can write CD-RW: 1
Can read DVD: 1
Can write DVD-R: 1
Can write DVD-RAM: 1
Can read MRW: 1
Can write MRW: 1
Can write RAM: 1
$
[/bash]
FROM MANUAL
udev supplies the system software with device events, manages permissions of device nodes and may create additional symlinks in the /dev directory, or renames network interfaces. The kernel usually just assigns unpredictable device names based on the order of discovery. Meaningful symlinks or network device names provide away to reliably identify devices based on their properties or current configuration. The udev daemon, udevd(8), receives device uevents directly from the kernel whenever a device is added or removed from the system, or it changes its state. When udev receives a device event, it matches its configured set of rules against various device attributes to identify the device. Rules that match may provide additional device information to be stored in the udev database or to be used to create meaningful symlink names. All device in formation udev processes is stored in the udev database and sent out to possible event subscribers. Access to all stored data and the event sources is provided by the library libudev. source: Manual
LINKS
https://www.linux.com/news/udev-introduction-device-management-modern-linux-system
https://en.wikipedia.org/wiki/Udev
https://www.thegeekdiary.com/beginners-guide-to-udev-in-linux/
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