What is "modloop" option in Alpine?
I'm trying to understand what is the difference of making Alpine installation medium as read-only type (LiveCD) and as a standard disk mode (where the OS state can be saved). I've seen the modloop
option when the author of this article (https://wiki.alpinelinux.org/wiki/Create_UEFI_boot_USB) configured loader entries for UEFI boot mode:
Contents of loader/entries/alpine.conf
title Alpine Linux
linux /boot/vmlinuz-hardened
initrd /boot/initramfs-hardened
options modloop=/boot/modloop-hardened modules=loop,squashfs,sd-mod,usb-storage quiet
And the question is how options listed in this stanza modloop=/boot/modloop-hardened modules=loop,squashfs,sd-mod
are related to each other and what do they mean?
The modloop=
option specifies a SquashFS filesystem that gets mounted to /.modloop
by the init file /etc/init.d/modloop
and symlinked from /lib/modules
(or possibly union-mounted with the overlay - see the modloop
init script for details). It contains the full kernel module tree for the built kernel, not the more limited set included in the initramfs / initrd.
You might find these helpful to explore:
-
unsquashfs -l /boot/modloop-hardened
(to explore what will get mounted to/.modloop
) -
gzip -dc /boot/initramfs-hardened | cpio -it
(to explore the initramfs contents)