This file is indexed.

/usr/lib/update-notifier/package-system-locked is in update-notifier-common 0.154.1.

This file is owned by root:root, with mode 0o755.

The actual contents of the file can be viewed below.

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#!/bin/sh
# check if package system is locked
# return 0 if unlocked, 2 if locked, 1 on error
set -e

for f in /var/lib/dpkg/lock /var/cache/apt/archives/lock \
    /var/lib/apt/lists/lock /run/unattended-upgrades.lock; do
    [ -e $f ] || continue

    # fuser succeeds if there is at least one user
    if fuser $f; then
        exit 2
    fi
done

exit 0