Initramfs init
mkinitfs is a tool to create initramfs images. Initramfs images are small images which contain a small filesystem with everything required to boot Alpine. For example, when booting a setup with full disk encryption, the initramfs contains the binaries required to prompt for a password and mount the encrypted disk.
Usage
Under a running alpine machine, the following command can be used if for some reason the initramfs has not been created properly for a new kernel.
mkinitfs -c /etc/mkinitfs/mkinitfs.conf -b / <kernelvers>
The script is located in /sbin/ and is created with ash. It expects /lib/modules to be populated with the <kernelvers> listed. For variations on this command (e.g. for chroot) Search "mkinitfs".
initramfs init cmdline options
In addition to the kernel boot parameters are a number of parameters that the init script understands. These are documented in the mkinitfs-bootparam(7) man page.
Although you may specify your own init script when building an initramfs, these parameters allow for extensive control over the initial startup of an Alpine Linux system.