How To Make CustomRescueCD

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See also
Users may prefer using Gentoo's build tool catalyst to do this task. See Catalyst/Custom Media Image for more information.


This document will walk readers through the steps to create a Gentoo stage4 inside a squashfs and subsequently use it in a bootable ISO9660 image.

The steps are to make a Gentoo Install inside a directory. Add or remove packages to the usage needs. This will become customrescuecd-squash, which will be the root filesystem in the CD. This will then be packaged with a syslinux /boot to make the bootable ISO9660 image.

Burning the image to a CD or making a bootable USB stick will not be addressed.

Examine the structure of the ISO:

  • ./boot/grub/font.pf2
  • ./boot/grub/grub.cfg <-- Grub Configuration File for EFI BOOT
  • ./boot/grub/x86_64-efi
  • ./boot/grub/x86_64-efi/all_video.mod
  • ./boot/grub/x86_64-efi/efi_gop.mod
  • ./boot/grub/x86_64-efi/efi_uga.mod
  • ./boot/grub/x86_64-efi/gfxterm.mod
  • ./boot/grub/x86_64-efi/video.mod
  • ./boot/grub/x86_64-efi/videoinfo.mod
  • ./boot/grub/x86_64-efi/videotest.mod
  • ./boot/memtest86plus/memtest
  • ./boot/memtest86plus/memtest.bin <-- Memtest kernel for bios boot
  • ./boot/syslinux/chain.c32
  • ./boot/syslinux/syslinux.cfg <--- Main Syslinux Configuration File
  • ./boot/syslinux/customresccd.cfg
  • ./boot/syslinux/customresccd_head.cfg
  • ./boot/syslinux/customresccd_pxe.cfg
  • ./boot/syslinux/customresccd_sys.cfg
  • ./boot/syslinux/customresccd_tail.cfg
  • ./boot/syslinux/isohdpfx.bin <--- Syslinux MBR for Bios Boot
  • ./boot/syslinux/isolinux.bin <--- Syslinux Image
  • ./boot/syslinux/ <--- Syslinux Boot Catalogue
  • ./boot/syslinux/ldlinux.c32
  • ./boot/syslinux/ldlinux.sys
  • ./boot/syslinux/libcom32.c32
  • ./boot/syslinux/libutil.c32
  • ./boot/syslinux/memdisk
  • ./boot/syslinux/poweroff.c32
  • ./boot/syslinux/pxelinux.0
  • ./boot/syslinux/reboot.c32
  • ./boot/syslinux/vesamenu.c32
  • ./boot/syslinux/whichsys.c32
  • ./boot/x86_64/customrescue64 <-- CustomRescueCd KERNEL
  • ./customresccd/x86_64/customrescuecd.sfs <--- SquashFS
  • ./customresccd/x86_64/customrescuecd.sha512 <---- Sha512 of Squashfs
  • ./EFI/boot/bootx64.efi < ---- Grub Efi Executable for usb stick boot
  • ./EFI/customiso/grub.img <--- Grub Partition in append to iso for efi boot that contain .efi executable

Create The Work Space

It is recommended to keep two terminals open, one for the stage 4 chroot and another needed to create the squash and the iso ahead.

/mnt/customrescuecd-squash is for the stage4. This will be turned into a squashfs later.

/mnt/customrescuecd64 is for the files that will become the ISO9660 filesystem, including the squashfs above.

root #mkdir /mnt/customrescuecd-squash /mnt/customrescuecd64 /mnt/customrescuecd64/boot

Download a Gentoo Stage 3, unpack it to /mnt/customrescuecd-squash, and chroot into it and build the system following the Gentoo Handbook and other guides as necessary.

Install necessary tools to the system:

root #emerge -1avn squashfs-tools syslinux grub genkernel gentoo-sources

Build kernel

Use genkernel to make a kernel and initramfs, add extra parameters as necessary (see Genkernel for details):

root #genkernel --bootdir=/mnt/customrescuecd64/boot --firmware all

The customrescuecd64 directory must contain these subdirectories:

  • boot/syslinux
  • boot/grub/x86_64-efi
  • boot/memtest86plus
  • boot/x86_64
  • EFI/boot
  • EFI/customiso
  • customresccd/x86_64

Creating the squashfs

Make an excludes file with the following content.

FILE exclude.txt

Add any other files and directories to be excluded from the squashfs

Build the squashfs using the exclude.txt file created above:

root #mksquashfs /mnt/customresccd-squash/ /mnt/customrescuecd64/customresccd/x86_64/customrescuecd.sfs -wildcards -ef exclude.txt -b 1024K -comp xz -progress -processors 4 -Xdict-size 100%



Download the syslinux cfg from syslinux.cfg.tar.xz and explode into customrescuecd64/boot/syslinux/ the content of this directory must be the one that follow! All *.c32 and memdisk isolinux.bin pxelinux.0 isohdpfx.bin file, then copy the stage4 at folder /usr/share/syslinux/

  • customresccd_tail.cfg
  • poweroff.c32
  • customresccd_head.cfg
  • syslinux.cfg
  • pxelinux.0
  • reboot.c32
  • isohdpfx.bin
  • libcom32.c32
  • whichsys.c32
  • chain.c32
  • ldlinux.sys
  • memdisk
  • vesamenu.c32
  • isolinux.bin
  • customresccd_pxe.cfg
  • ldlinux.c32
  • customresccd_sys.cfg
  • customresccd.cfg
  • libutil.c32


in the directory customrescuecd64/boot/grub/x86_64-efi/ copy the files all_video.mod efi_gop.mod efi_uga.mod gfxterm.mod videoinfo.mod videotest.mod from /usr/lib/grub/x86_64-efi/ of your stage4

download the font.pf2 in the directory customrescuecd64/boot/grub/

Create the file /mnt/customrescuecd64/boot/grub/grub.cfg adjusting kernel and initramfs versions as necessary:

FILE /mnt/customrescuecd64/boot/grub/grub.cfg
set timeout=90
set default=0
set fallback=1
set pager=1

if loadfont /boot/grub/font.pf2 ; then
	set gfxmode=auto
	insmod efi_gop
	insmod efi_uga
	insmod gfxterm
	insmod all_video
	insmod videotest
	insmod videoinfo
	terminal_output gfxterm

menuentry "Boot CustomRescueCd" {
	set gfxpayload=keep
	linux /boot/vmlinuz-5.7.2-gentoo loop=/customresccd/x86_64/customrescuecd.sfs looptype=squashfs
	initrd /boot/initramfs-5.7.2-gentoo

cd into customrescuecd64/EFI/customiso/

create a empty file named grub.img to create the boot efi partition

root #dd if=/dev/zero of=grub.img bs=1M count=2

format it with FAT12 filesystem

root # mkfs.vfat -f 1 -F 12 grub.img

mount grub.img into /boot/efi of your stage4

root # mount -t vfat grub.img customrescuecd-squash/boot/efi/

from your stage4 chroot

root # mkdir -p /boot/efi/efi/boot
root # cd /boot/efi/efi/boot

create the grub image efi boot executable

root # grub-mkimage -o bootx64.efi -O x86_64-efi -p /boot/grub boot linux linux16 normal configfile part_gpt part_msdos fat iso9660 udf test keystatus loopback regexp probe efi_gop efi_uga all_video gfxterm font echo read help ls cat halt reboot