/usr/share/acl2-6.3/books/std/io/ is in acl2-books-certs 6.3-5.
This file is owned by root:root, with mode 0o755.
..
/usr/share/acl2-6.3/books/std/io/base.cert
/usr/share/acl2-6.3/books/std/io/combine.cert
/usr/share/acl2-6.3/books/std/io/file-measure.cert
/usr/share/acl2-6.3/books/std/io/nthcdr-bytes.cert
/usr/share/acl2-6.3/books/std/io/read-file-bytes.cert
/usr/share/acl2-6.3/books/std/io/read-file-characters-no-error.cert
/usr/share/acl2-6.3/books/std/io/read-file-characters.cert
/usr/share/acl2-6.3/books/std/io/read-file-lines.cert
/usr/share/acl2-6.3/books/std/io/read-file-objects.cert
/usr/share/acl2-6.3/books/std/io/read-ints.cert
/usr/share/acl2-6.3/books/std/io/read-object.cert
/usr/share/acl2-6.3/books/std/io/signed-byte-listp.cert
/usr/share/acl2-6.3/books/std/io/take-bytes.cert
/usr/share/acl2-6.3/books/std/io/top.cert
/usr/share/acl2-6.3/books/std/io/unsigned-byte-listp.cert