Why use cpio for initramfs

In general there has to be some kind of protocol because typically it is not enough to just load a file into memory and jump at a specific location but you have to either pass additional arguments like kernel parameters, i.e. accessing memdisk arguments from DOS.

As this is hardware dependent (arm is different than x86 for instance) you have to find the correct information, see this article about booting arm or the Linux/x86 boot protocol for some examples.

After reading this post, the problem is solved!

I had noticed when running the mount command that two entries appeared for /:

rootfs on / type rootfs (rw,relatime)
devtmpfs on /dev type devtmpfs (rw,relatime,size=209064k,nr_inodes=52266,mode=755)
proc on /proc type proc (rw,relatime)
devpts on /dev/pts type devpts (rw,relatime,gid=5,mode=620)
tmpfs on /dev/shm type tmpfs (rw,relatime,mode=777)
tmpfs on /tmp type tmpfs (rw,relatime)
sysfs on /sys type sysfs (rw,relatime)
none on / type tmpfs (rw,relatime)

I had added an entry to fstab that I needed to remove:

# /etc/fstab: static file system information.
#
# <file system> <mount pt>     <type>   <options>         <dump> <pass>
none            /              tmpfs    defaults          0      0
proc            /proc          proc     defaults          0      0
devpts          /dev/pts       devpts   defaults,gid=5,mode=620   0      0
tmpfs           /dev/shm       tmpfs    mode=0777         0      0
tmpfs           /tmp           tmpfs    defaults          0      0
sysfs           /sys           sysfs    defaults          0      0

After removing the entry (and performing a reboot):

none            /              tmpfs    defaults          0      0

The problem goes away!