Is it possible to install a system directly from an ISO without using an installer?

Here is the grub menu entry. You can write it into /boot/grub/custom.cfg, then it won’t be overwritten by any grub update.
The entry below assumes the ISO file exists under folder /ISO in the drive where you copy it. Line set isofile=... can be changed if you want to use another folder.
Additional note: the menu entry assumes Intel CPU. If you have an AMD CPU, change the microcode name on the initrd line.

menuentry 'Boot endeavouros-2021.04.17-x86_64.iso' {
    set isofile=/ISO/endeavouros-2021.04.17-x86_64.iso
    search --no-floppy --set=root --file $isofile
    probe -u $root --set=uuid
    loopback loop $isofile
    linux (loop)/arch/boot/x86_64/vmlinuz-linux img_dev=/dev/disk/by-uuid/$uuid img_loop=$isofile
    initrd  (loop)/arch/boot/intel-ucode.img (loop)/arch/boot/x86_64/archiso.img
}
2 Likes