quiet loglevel=3(略)
上記の設定は quiet と loglevel=の両方を、この順番で使用したときにのみ適用されます (quiet が先)。
めも
https://www.kernel.org/doc/Documentation/admin-guide/kernel-parameters.txt
All Kernel Messages with a loglevel smaller than the
console loglevel will be printed to the console. It can
also be changed with klogd or other programs.