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#
# For both initrd variants it is assumed the root filesystem files are
# located at /home/devel/rootfs ...
#
# To create the archive-based initial ramdisk:
cd /home/devel/rootfs
find . | cpio -o -H newc | gzip -9c > ../initrd.cpio.gz
# To create the image-based initial ramdisk:
dd if=/dev/zero of=initrd.img bs=4M count=1
/sbin/mkfs.ext2 initrd.img
sudo mount -o loop initrd.img /mnt
sudo cp -a /home/devel/rootfs/. /mnt/
sudo umount /mnt
gzip -9 initrd.img
#
# The image-based initial ramdisk is the old way of doing things. It
# really has no advantages. But it does have disadvantages:
#
# - the size if limited by the image
# - the size is limited by the kernel configurations
# (CONFIG_BLK_DEV_RAM, CONFIG_BLK_DEV_RAM_SIZE)
# - the kernel root= parameter must be set to /dev/ram0
# (an initrd is the root filesystem, i.e. /sbin/init is called)
# - the real root filesystem must unmount it after pivot_root
# (which means the real root filesystem has knowledge of an initrd)
#
# The archive-based initial ramdisk has the following differences/advantages:
#
# - very simple to create (no root rights required!)
# - uses exactly as much RAM as needed (grows dynamically)
# - does not require any special boot arguments
# - does not need to be "cleaned up" after switch_root
# (the real root filesystem has no knowledge that an initrd existed)
# - the kernel calls /init instead of /sbin/init
# - /dev/console is required if replacing the built-in initramfs
#
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