/lib/udev/rules.d/75-cd-aliases-generator.rules is in udev 175-0ubuntu9.
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 | # these rules generate rules for the /dev/{cdrom,dvd,...} symlinks
# the "path" of usb/ieee1394 devices changes frequently, use "id"
ACTION=="add", SUBSYSTEM=="block", SUBSYSTEMS=="usb|ieee1394", ENV{ID_CDROM}=="?*", ENV{GENERATED}!="?*", \
PROGRAM="write_cd_rules by-id", SYMLINK+="%c", GOTO="persistent_cd_end"
ACTION=="add", SUBSYSTEM=="block", ENV{ID_CDROM}=="?*", ENV{GENERATED}!="?*", PROGRAM="write_cd_rules", SYMLINK+="%c"
LABEL="persistent_cd_end"
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