/lib/udev/rules.d/80-mm-candidate.rules is in modemmanager 1.4.0-1.
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 | # do not edit this file, it will be overwritten on update
# Tag any devices that MM might be interested in; if ModemManager is started
# up right after udev, when MM explicitly requests devices on startup it may
# get devices that haven't had all rules run yet. Thus, we tag devices we're
# interested in and when handling devices during MM startup we ignore any
# that don't have this tag. MM will still get the udev 'add' event for the
# device a short while later and then process it as normal.
ACTION!="add|change|move", GOTO="mm_candidate_end"
SUBSYSTEM=="tty", ENV{ID_MM_CANDIDATE}="1"
SUBSYSTEM=="net", ENV{ID_MM_CANDIDATE}="1"
KERNEL=="cdc-wdm*", SUBSYSTEM=="usb", ENV{ID_MM_CANDIDATE}="1"
KERNEL=="cdc-wdm*", SUBSYSTEM=="usbmisc", ENV{ID_MM_CANDIDATE}="1"
LABEL="mm_candidate_end"
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