Why does apt-file report "The cache is empty" even after running "apt-file update"?

Does anybody know why apt-file reports that the cache is empty even after running apt-file update and apt update? [pop-os ~][I]% apt-file search /usr/lib/android-sdk/tools/bin/sdkmanager E: The cache is empty. You need to run "apt update" first. [pop-os ~][I]% apt-file update Reading package lists... Done E: Could not open lock file /var/lib/apt/lists/lock - open (13: Permission denied) E: Unable to lock directory /var/lib/apt/lists/ W: Problem unlinking the file /var/cache/apt/pkgcache.bin - RemoveCaches (13: Permission denied) W: Problem unlinking the file /var/cache/apt/srcpkgcache.bin - RemoveCaches (13: Permission denied) [pop-os ~][I]% sudo !! sudo apt-file update Hit:1 http://apt.pop-os.org/proprietary cosmic InRelease Hit:2 http://us.archive.ubuntu.com/ubuntu cosmic InRelease Hit:3 http://us.archive.ubuntu.com/ubuntu cosmic-updates InRelease Hit:4 http://ppa.launchpad.net/nextcloud-devs/client/ubuntu cosmic InRelease Hit:5 http://us.archive.ubuntu.com/ubuntu cosmic-security InRelease Hit:6 http://repository.spotify.com stable InRelease Hit:7 http://us.archive.ubuntu.com/ubuntu cosmic-backports InRelease Get:8 http://apt.pop-os.org/proprietary cosmic all Contents (deb) [102 kB] Hit:9 http://ppa.launchpad.net/system76/pop/ubuntu cosmic InRelease Get:10 http://us.archive.ubuntu.com/ubuntu cosmic amd64 Contents (deb) [40.9 MB] Get:11 http://apt.pop-os.org/proprietary cosmic i386 Contents (deb) [276 B] Get:12 http://apt.pop-os.org/proprietary cosmic amd64 Contents (deb) [2,605 kB] Get:13 http://us.archive.ubuntu.com/ubuntu cosmic i386 Contents (deb) [40.2 MB] Get:14 http://us.archive.ubuntu.com/ubuntu cosmic-updates i386 Contents (deb) [5,178 kB] Get:15 http://us.archive.ubuntu.com/ubuntu cosmic-updates amd64 Contents (deb) [6,997 kB] Get:16 http://us.archive.ubuntu.com/ubuntu cosmic-security i386 Contents (deb) [3,784 kB] Get:17 http://us.archive.ubuntu.com/ubuntu cosmic-security amd64 Contents (deb) [5,296 kB] Get:18 http://us.archive.ubuntu.com/ubuntu cosmic-backports amd64 Contents (deb) [3,773 B] Get:19 http://us.archive.ubuntu.com/ubuntu cosmic-backports i386 Contents (deb) [3,772 B] Fetched 105 MB in 21s (4,952 kB/s) Reading package lists... Done Building dependency tree Reading state information... Done 148 packages can be upgraded. Run 'apt list --upgradable' to see them. sudo -E apt-file update 20.30s user 1.16s system 95% cpu 22.585 total [pop-os ~][I]% apt-file search /usr/lib/android-sdk/tools/bin/sdkmanager E: The cache is empty. You need to run "apt update" first. [pop-os ~][I]% apt update Reading package lists... Done E: Could not open lock file /var/lib/apt/lists/lock - open (13: Permission denied) E: Unable to lock directory /var/lib/apt/lists/ W: Problem unlinking the file /var/cache/apt/pkgcache.bin - RemoveCaches (13: Permission denied) W: Problem unlinking the file /var/cache/apt/srcpkgcache.bin - RemoveCaches (13: Permission denied) [pop-os ~][I]% sudo !! sudo apt update Hit:1 http://apt.pop-os.org/proprietary cosmic InRelease Hit:2 http://us.archive.ubuntu.com/ubuntu cosmic InRelease Hit:3 http://us.archive.ubuntu.com/ubuntu cosmic-updates InRelease Hit:4 http://us.archive.ubuntu.com/ubuntu cosmic-security InRelease Hit:5 http://ppa.launchpad.net/nextcloud-devs/client/ubuntu cosmic InRelease Hit:6 http://us.archive.ubuntu.com/ubuntu cosmic-backports InRelease Get:7 http://apt.pop-os.org/proprietary cosmic i386 Contents (deb) [276 B] Hit:8 http://repository.spotify.com stable InRelease Get:9 http://apt.pop-os.org/proprietary cosmic all Contents (deb) [102 kB] Hit:10 http://ppa.launchpad.net/system76/pop/ubuntu cosmic InRelease Get:11 http://us.archive.ubuntu.com/ubuntu cosmic amd64 Contents (deb) [40.9 MB] Get:12 http://apt.pop-os.org/proprietary cosmic amd64 Contents (deb) [2,605 kB] Get:13 http://us.archive.ubuntu.com/ubuntu cosmic i386 Contents (deb) [40.2 MB] Get:14 http://us.archive.ubuntu.com/ubuntu cosmic-updates i386 Contents (deb) [5,178 kB] Get:15 http://us.archive.ubuntu.com/ubuntu cosmic-updates amd64 Contents (deb) [6,997 kB] Get:16 http://us.archive.ubuntu.com/ubuntu cosmic-security amd64 Contents (deb) [5,296 kB] Get:17 http://us.archive.ubuntu.com/ubuntu cosmic-security i386 Contents (deb) [3,784 kB] Get:18 http://us.archive.ubuntu.com/ubuntu cosmic-backports i386 Contents (deb) [3,772 B] Get:19 http://us.archive.ubuntu.com/ubuntu cosmic-backports amd64 Contents (deb) [3,773 B] Fetched 105 MB in 21s (4,963 kB/s) Reading package lists... Done Building dependency tree Reading state information... Done 148 packages can be upgraded. Run 'apt list --upgradable' to see them. sudo -E apt update 20.24s user 1.15s system 95% cpu 22.470 total [pop-os ~][I]% apt-file search /usr/lib/android-sdk/tools/bin/sdkmanager E: The cache is empty. You need to run "apt update" first. [pop-os ~][I]% sudo !! sudo apt-file search /usr/lib/android-sdk/tools/bin/sdkmanager E: The cache is empty. You need to run "apt update" first. Distro is Pop!_OS (an Ubuntu derivative), but I couldn't find a Pop!_OS tag.