There are three ways you can change the behaviour of the init system. Those are:
On GRUB, you can edit the kernel command line parameters, which will be parsed as variables on the init system. Not all of the parameters will be acted upon, but all of them will be set as variables on the init script. For example an example command line, and how it is interpreted.
BOOT_IMAGE=/boot/vmlinuz root=/dev/sda2 rw loglevel=3 quiet
This command line will be parsed to set the following variables:
BOOT_IMAGE=/boot/vmlinuz root=/dev/sda2 rw=1 loglevel=3 quiet=1
Some of these variables, such as
quiet, will be used by the init system to change the behaviour of the
However, the kernel command line isn’t the only place to set your boot parameters. You can specify variables here as well, although note that the kernel command line always gets the priority for these variables since they can be set just before boot.