/etc/init/plymouth-log.conf is in plymouth 0.8.8-0ubuntu17.
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 | # plymouth-log - Flush boot log to disk
#
# plymouth buffers console messages during boot, once the filesystem
# is up they should be flushed to the boot log on disk and further
# messages written directly to it.
description "Flush boot log to disk"
start on filesystem
task
exec /bin/plymouth update-root-fs --read-write
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