7.5. Building ISOs

Since Cobbler uses the systemd hardening option “PrivateTmp” you can’t write or read files from your /tmp when you run Cobbler via systemd as a service.

Per default this builds an ISO for all available systems and profiles.

If you want to generate multiple ISOs you need to execute this command multiple times (with different --iso names).

7.5.1. Under the hood

Under the hood the tool “xorriso” is used. It is being executed in the “mkisofs” (the predecessor) compatibility mode. Thus we don’t execute “mkisofs” anymore. Please be aware of this when adding CLI options.

On the Python side we are executing the following command:

xorriso -as mkisofs $XORRISOFS_OPTS -isohybrid-mbr $ISOHDPFX_location -c isolinux/boot.cat \
  -b isolinux/isolinux.bin -no-emul-boot -boot-load-size 4 -boot-info-table -eltorito-alt-boot \
  -e $EFI_IMG_LOCATION -no-emul-boot -isohybrid-gpt-basdat -V \"Cobbler Install\" \
  -o $ISO $BUILDISODIR

Explanation what this command is doing:

xorriso -as mkisofs \
  -isohybrid-mbr /usr/share/syslinux/isohdpfx.bin \  # --> Makes the image MBR bootable and specifies the MBR File
  -c isolinux/boot.cat \                             # --> Boot Catalog -> Automatically created according to Syslinux wiki
  -b isolinux/isolinux.bin \                         # --> Boot file which is manipulated by mkisofs/xorriso
  -no-emul-boot \                                    # --> Does not run in emulated disk mode when being booted
  -boot-load-size 4 \                                # --> Size of 512 sectors to boot in no-emulation mode
  -boot-info-table \                                 # --> Store CD layout in the image
  -eltorito-alt-boot \                               # --> Allows to have more then one El Torito boot on a CD
  -e /var/lib/cobbler/loaders/grub/x64.efi \         # --> Boot image file which is EFI bootable, relative to root directory
  -no-emul-boot \                                    # --> See above
  -isohybrid-gpt-basdat \                            # --> Add GPT additionally to MBR
  -V "Cobbler Install" \                             # --> Name when the image is recognized by the OS
  -o /root/generated.iso \                           # --> Produced ISO file name and path
  /var/cache/cobbler/buildiso                        # --> Root directory for the build

7.5.2. Common options for building ISOs

  • --iso: This defines the name of the built ISO. It defaults to autoinst.iso.

  • --distro: Used to detect the architecture of the ISO you are building. Specifies also the used Kernel and Initrd.

  • --buildisodir: The temporary directory where Cobbler will build the ISO. If you have enough RAM to build the ISO you should really consider using a tmpfs for performance.

  • --profiles: Modify the profiles Cobbler builds ISOs for. If this is omitted, ISOs for all profiles will be built.

  • --xorrisofs-opts: The options which are passed to xorriso additionally to the above shown.

7.5.3. Building standalone ISOs

have to provide the following parameters:

  • --standalone: If this flag is present, Cobbler will build an ISO which can be installed without network access.

  • --airgapped: If this flag is present, Cobbler will build an ISO which contains all mirrored repositories for extended installations.

  • --source: The directory with the sources for the image.

7.5.4. Building net-installer ISOs

You have to provide the following parameters:

  • --systems: Filter the systems you want to build the ISO for.

  • --exclude-dns: Flag to add the nameservers (and other DNS information) to the append line or not.

7.5.5. Examples

Building exactly one network installer ISO for a specific profile (suitable for all underlying systems):

Building exactly one network installer ISO for a specific system:

Building exactly one airgapped installable ISO for a specific system: