/usr/share/acl2-6.3/books/hacking/ is in acl2-books-certs 6.3-5.
This file is owned by root:root, with mode 0o755.
..
/usr/share/acl2-6.3/books/hacking/all.cert
/usr/share/acl2-6.3/books/hacking/bridge.cert
/usr/share/acl2-6.3/books/hacking/defcode.cert
/usr/share/acl2-6.3/books/hacking/defstruct-parsing.cert
/usr/share/acl2-6.3/books/hacking/doc-section.cert
/usr/share/acl2-6.3/books/hacking/dynamic-make-event-test.cert
/usr/share/acl2-6.3/books/hacking/dynamic-make-event.cert
/usr/share/acl2-6.3/books/hacking/evalable-ld-printing.cert
/usr/share/acl2-6.3/books/hacking/hacker.cert
/usr/share/acl2-6.3/books/hacking/progn-bang-enh.cert
/usr/share/acl2-6.3/books/hacking/raw.cert
/usr/share/acl2-6.3/books/hacking/redefun.cert
/usr/share/acl2-6.3/books/hacking/rewrite-code.cert
/usr/share/acl2-6.3/books/hacking/subsumption.cert
/usr/share/acl2-6.3/books/hacking/table-guard.cert