2. Working with ISO Images

Procedure 1. Extracting ISO Images

1. Mount the downloaded image.

   # mount -t iso9660 -o loop path/to/image.iso /mnt/iso

   Replace path/to/image.iso with the path to the downloaded ISO. Also make sure that the target directory (/mnt/iso) exists and nothing else is currently mounted there.
2. Create a working directory - a directory where you want to place the contents of the ISO image.

   $ mkdir /tmp/ISO

3. Copy all contents of the mounted image to your new working directory. Make sure to use the -p option to preserve file and directory permissions and ownership.

   # cp -pRf /mnt/iso /tmp/ISO

4. Unmount the image.

   # umount /mnt/iso

Procedure 2. Creating product.img

1. Navigate to a working directory such as /tmp, and create a subdirectory named product/:

   $ cd /tmp

   $ mkdir product/

2. Create a directory structure which is identical to the location of the file you want to replace. For example, if you want to test an add-on, which belongs in the /usr/share/anaconda/addons directory on the installation system; create the same structure in your working directory:

   $ mkdir -p product/usr/share/anaconda/addons

   Note

   You can browse the installer's runtime file system by booting the installation, switching to virtual console 1 (Ctrl+Alt+F1) and then switching to the second tmux window (Ctrl+b 2). This opens a shell prompt which you can use to browse the file system.
3. Place your customized files (in this example, custom add-on for Anaconda) into the newly created directory:

   $ cp -r ~/path/to/custom/addon/ product/usr/share/anaconda/addons/

4. Repeat the two steps above (create a directory structure and move modified files into it) for every file you want to add to the installer.
5. Create a .buildstamp file in the root of the directory which will become the product.img file. The .buildstamp file describes the system version and several other parameters. The following is an example of a .buildstamp file from Red Hat Enterprise Linux 7.4:

   [Main]
   Product=Red Hat Enterprise Linux
   Version=7.4
   BugURL=https://bugzilla.redhat.com/
   IsFinal=True
   UUID=201707110057.x86_64
   [Compose]
   Lorax=19.6.92-1
   

   Note the IsFinal parameter, which specifies whether the image is for a release (GA) version of the product (True), or a pre-release such as Alpha, Beta, or an internal milestone (False).
6. Change into the product/ directory, and create the product.img archive:

   $ cd product

   $ find . | cpio -c -o | gzip -9cv > ../product.img

   This creates a product.img file one level above the product/ directory.
7. Move the product.img file to the images/ directory of the extracted ISO image.

Procedure 3. Creating ISO Images

1. Make sure that all of your changes are included in the working directory. For example, if you are testing an add-on, make sure to place the product.img in the images/ directory.
2. Make sure your current working directory is the top-level directory of the extracted ISO image - e.g. /tmp/ISO/iso.
3. Create the new ISO image using genisoimage:

   # genisoimage -U -r -v -T -J -joliet-long -V "RHEL-7.1 Server.x86_64" -volset "RHEL-7.1 Server.x86_64" -A "RHEL-7.1 Server.x86_64" -b isolinux/isolinux.bin -c isolinux/boot.cat -no-emul-boot -boot-load-size 4 -boot-info-table -eltorito-alt-boot -e images/efiboot.img -no-emul-boot -o ../NEWISO.iso .

   In the above example:
   • Make sure that values for the -V, -volset, and -A options match the image's boot loader configuration, if you are using the LABEL= directive for options which require a location to load a file on the same disk. If your boot loader configuration (isolinux/isolinux.cfg for BIOS and EFI/BOOT/grub.cfg for UEFI) uses the inst.stage2=LABEL=disk_label stanza to load the second stage of the installer from the same disk, then the disk labels must match.

     Important

     In boot loader configuration files, replace all spaces in disk labels with \x20. For example, if you create an ISO image with a label of RHEL 7.1, boot loader configuration should use RHEL\x207.1 to refer to this label.
   • Replace the value of the -o option (-o ../NEWISO.iso) with the file name of your new image. The value in the example will create file NEWISO.iso in the directory above the current one.
   For more information about this command, see the genisoimage(1) man page.
4. Implant an MD5 checksum into the image. Without performing this step, image verification check (the rd.live.check option in the boot loader configuration) will fail and you will not be able to continue with the installation.

   # implantisomd5 ../NEWISO.iso

   In the above example, replace ../NEWISO.iso with the file name and location of the ISO image you have created in the previous step.