/usr/lib/tmpfiles.d/journal-nocow.conf is in systemd 229-4ubuntu4.
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 18 19 20 21 22 23 24 25 26 27 | # This file is part of systemd.
#
# systemd is free software; you can redistribute it and/or modify it
# under the terms of the GNU Lesser General Public License as published by
# the Free Software Foundation; either version 2.1 of the License, or
# (at your option) any later version.
# See tmpfiles.d(5) for details
# Set the NOCOW attribute for directories of journal files. This flag
# is inheredited by their new files and sub-directories. Matters only
# for btrfs filesystems.
#
# WARNING: Enabling the NOCOW attribute improves journal performance
# substantially, but also disables the btrfs checksum logic. In
# btrfs RAID filesystems the checksums are needed for rebuilding
# corrupted files. Without checksums such rebuilds are not
# possible.
#
# In a single-disk filesystem (or a filesystem without redundancy)
# enabling the NOCOW attribute for journal files is safe, because
# they have their own checksums and a rebuilding wouldn't be possible
# in any case.
h /var/log/journal - - - - +C
h /var/log/journal/%m - - - - +C
h /var/log/journal/remote - - - - +C
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