/lib/udev/rules.d/60-cdrom_id.rules is in udev 229-4ubuntu4.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 | # 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 $devnode", 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 $devnode"
# ejecting a CD does not remove the device node, so mark the systemd device
# unit as inactive while there is no medium; this automatically cleans up of
# stale mounts after ejecting
ENV{DISK_MEDIA_CHANGE}=="?*", ENV{ID_CDROM_MEDIA}!="?*", ENV{SYSTEMD_READY}="0"
KERNEL=="sr0", SYMLINK+="cdrom", OPTIONS+="link_priority=-100"
LABEL="cdrom_end"
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