Remastering the Install ISO

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Remastering the official Arch Linux install ISO image is not necessary for most applications. However, it may be desirable in some cases.

  • Basic hardware is not supported by the core install. (rare)
  • Installation on a non-internet capable machine.
  • Deployment of Arch Linux on many similar machines, requiring the same installation procedure.

As these ISOs are bootable, they can also be used for system rescue, testing, project demos, and more.


It is often preferable to rebuild the installation ISO with Archiso, instead of remastering an existing ISO.


How it works

The installer ISO used to contain two separate archlinux systems. One for 32 bit (i686) and one for 64 bit (x86_64). Now only 64 bit system is supported. The root filesystems of this system is stored in arch/x86_64/airootfs.sfs. The kernel and initramfs are in arch/boot/x86_64.

When booting, the initramfs will search for the device it was booted from via its label, ARCH_201410 for example, and will mount the root filesystem for the architecture.

Extracting the ISO

To remaster the Arch Linux ISO, you will need a copy of the original ISO image. Download it from the download page

Now, create a new directory to mount the ISO:

# mkdir /mnt/archiso

Mount the ISO to this directory (due to the nature of ISOs, the result is read-only):

# mount -t iso9660 -o loop /path/to/archISO /mnt/archiso

Copy the contents to another directory, where they can be edited:

$ cp -a /mnt/archiso ~/customiso
Note: Make sure customiso does not exist beforehand, otherwise this will create a subdirectory called archiso inside customiso


Modifying the x86_64 system

Change into the directory of the x86_64 system:

 $ cd ~/customiso/arch/x86_64

Unsquash airootfs.sfs (to squashfs-root):

 $ unsquashfs airootfs.sfs
Note: You need squashfs-tools in order to do that.

Now you can modify the content of the system in squashfs-root. You can also chroot into this system to install packages etc.:

 # arch-chroot squashfs-root /bin/bash
Note: arch-chroot is part of the package arch-install-scripts
Note: If the arch-chroot script is not available in your system (e.g, when remastering arch-based distros), mount the api file systems and copy over your DNS details. See Chroot#Using chroot.

To be able to install package, you have to initialise the pacman keyring:

 (chroot) # pacman-key --init
 (chroot) # pacman-key --populate archlinux
Note: This step can take quite a while, be patient. (see Pacman-Key)

If the kernel or initrd is updated, additional steps are required. In this case you have to install archiso inside the chroot and change the content of /etc/mkinitcpio.conf:

 (chroot) # pacman -Syu --force archiso linux
 (chroot) # nano /etc/mkinitcpio.conf

Change the line that says HOOKS="... to:

 HOOKS="base udev memdisk archiso_shutdown archiso archiso_loop_mnt archiso_pxe_common archiso_pxe_nbd archiso_pxe_http archiso_pxe_nfs archiso_kms block pcmcia filesystems keyboard"

Now update the initramfs:

 (chroot) # mkinitcpio -p linux

When you are done, create a list of all installed packages, clean the pacman cache and exit the chroot:

 (chroot) # LANG=C pacman -Sl | awk '/\[installed\]$/ {print $1 "/" $2 "-" $3}' > /pkglist.txt
 (chroot) # pacman -Scc
 (chroot) # exit

If you updated the kernel or the initramfs, copy them over to the system:

 $ cp squashfs-root/boot/vmlinuz-linux ~/customiso/arch/boot/x86_64/vmlinuz
 $ cp squashfs-root/boot/initramfs-linux.img ~/customiso/arch/boot/x86_64/archiso.img

Move the list of packages:

 $ mv squashfs-root/pkglist.txt ~/customiso/arch/pkglist.x86_64.txt

Now recreate airootfs.sfs:

 $ rm airootfs.sfs
 $ mksquashfs squashfs-root airootfs.sfs


 # rm -r squashfs-root

Now update the MD5 checksum of airootfs.sfs:

 $ md5sum airootfs.sfs > airootfs.md5

Modifying the EFI boot image

If you have updated the kernel or the initramfs and wish to boot on EFI systems, update the EFI boot image. You will need dosfstools as the EFI boot image is a FAT16 filesystem.

 $ mkdir mnt
 # mount -t vfat -o loop ~/customiso/EFI/archiso/efiboot.img mnt
 # cp ~/customiso/arch/boot/x86_64/vmlinuz mnt/EFI/archiso/vmlinuz.efi
 # cp ~/customiso/arch/boot/x86_64/archiso.img mnt/EFI/archiso/archiso.img

If you see No space left on device errors, you might need to resize efiboot.img. You can also create a new efiboot.img and copy the old files (replace 50 with the required size).

 $ dd if=/dev/zero bs=1M count=50 of=efiboot-new.img
 $ mkfs.fat -n "ARCHISO_EFI" efiboot-new.img
 $ mkdir new
 # mount -t fat -o loop efiboot-new.img new
 $ cp -r mnt/* new/
 # umount new mnt
 $ mv efiboot-new.img ~/customiso/EFI/archiso/efiboot.img

And use the new efiboot.img as above.

Create a new ISO

Create a new ISO image with genisoimage, which is part of cdrtools, as a symlink to mkisofs.

$ genisoimage -l -r -J -V "ARCH_201209" -b isolinux/isolinux.bin -no-emul-boot -boot-load-size 4 -boot-info-table -c isolinux/ -o ../arch-custom.iso ./
Note: The ISO label must remain the same as the original label (in this case ARCH_201209) for the image to boot successfully.
Note: The -b and -c options expect paths relative to the root of the ISO

The resulting ISO image will boot only from CD, DVD or BD. For booting from USB stick or hard disk, it needs the isohybrid feature. This can be achieved by postprocessing the ISO by program isohybrid included in syslinux. Officially, the version of installed SYSLINUX has to be the same as the version of /isolinux/isolinux.bin in the ISO. It is not known whether really incompatible version combinations exist.

An alternative to genisoimage plus isohybrid can be derived from the xorriso run of mkarchiso.

$ iso_label="ARCH_201209"
$ xorriso -as mkisofs \
       -iso-level 3 \  
       -full-iso9660-filenames \
       -volid "${iso_label}" \
       -eltorito-boot isolinux/isolinux.bin \
       -eltorito-catalog isolinux/ \
       -no-emul-boot -boot-load-size 4 -boot-info-table \
       -isohybrid-mbr ~/customiso/isolinux/isohdpfx.bin \
       -output arch-custom.iso \ 

Option -isohybrid-mbr needs an MBR template file. Most probably there is already such a file /isolinux/isohdpfx.bin in the original ISO, which matches the SYSLINUX version used in the ISO. Only if this file is missing in the copied ISO content, it has to be cut out of the original ISO image file, before above xorriso run is performed:

$ dd if=/path/to/archISO bs=512 count=1 of=~/customiso/isolinux/isohdpfx.bin

If the original ISO supports bootability via EFI, this can be activated in the new ISO by inserting the following options between the lines "-isohybrid-mbr ..." and "-output ...":

       -eltorito-alt-boot \
       -e EFI/archiso/efiboot.img \
       -no-emul-boot -isohybrid-gpt-basdat \

The file /EFI/archiso/efiboot.img is a FAT filesystem image file. If it is missing in the original ISO, then there was no EFI support in that ISO.

The newly created ISO image arch-custom.iso is found in the home directory. You can write the ISO image to a USB stick as explained in USB Installation Media. Alternatively you can burn the ISO image on a CD, DVD, or BD with your preferred software. On Arch, that is covered in the article about burning an ISO image.

See also