Directly booting an ISO file

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It is technically possible to boot an .iso file directly, without flashing it to a disk or device.

Using a virtual machine

The QEMU page shows how an ISO image and .apkovl customizations are booted with a virtual machine. This works very well with Proxmox as well - just attach the ISO and Alpine boots to RAM on startup. You can customize your .iso file by building a custom ISO image by following the instructions on How to make a custom ISO image with mkimage

Using an installed Bootloader

grub-imageboot

In addition to standard partitions or drives, the Debian package grub-imageboot allows booting .iso files placed in the /boot/images directory.

Manual Grub menu entry

Suppose Alpine ISO image is stored in partition 1 of a disk or SSD in directory /boot and the installed Linux in that partition has GRUB2.

Then insert the following in /etc/grub.d/40_custom:

menuentry 'Alpine Linux 3.22 (loopback from /dev/sda1)' --class alpine --class gnu-linux --class gnu --class os {
       echo            Device:      $root
       set             isofile=/boot/alpine-extended-3.22.1-x86_64.iso
       loopback        lb $isofile
       echo            ISO root:       $root
       echo            ISO image:      $isofile
       echo            "Alpine Linux 3.22 is booting from $isofile"
       echo            'loading the kernel'
       linux           (lb)/boot/vmlinuz-lts
       echo            'loading initial root filesystem'
       initrd          (lb)/boot/initramfs-lts
}

Alternatively the statements loopback, linux and initrd can be entered manually in GRUB2 commandline.

Create a new GRUB2 configuration file:

# grub-mkconfig -o /boot/grub/grub.cfg

# reboot

Select created menu entry.

Boot will work until boot media is to be mounted:

Mounting boot media: failed
initramfs emergency recovery shell launched

So mount it manually:

# mount /dev/sda1 /media/sda1
# mount -o loop -t iso9660 /media/sda1/boot/alpine-extended-3.22.1-x86_64.iso /media/cdrom
# exit

Then login as root and

# setup-alpine

syslinux

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