ISOwithKS

Goal: Create a framework to automate the production of customized RedHat/CentOS ISOs to aid deployment to bare-metal systems where network boot options are not available.

Usage

Execute the make_iso.sh script, then answer the questions.

• The script must run as root, enter your password for sudo if prompted.
• Choose the full name of the ISO to start with, then enter the entire ISO name presented.

The script will execute on any errors, so a successfull run should end with something like this:

Built ISO available here:
/opt/rh/tmp/rhel-server-7.4-x86_64-dvd_tempdir/custom-rhel-server-7.4-x86_64-dvd.20180305_112238.iso
-rw-r--r-- 1 root root 4183703552 Mar  5 11:22 /opt/rh/tmp/rhel-server-7.4-x86_64-dvd_tempdir/custom-rhel-server-7.4-x86_64-dvd.20180305_112238.iso
-rw-r--r-- 1 root root        168 Mar  5 11:23 /opt/rh/tmp/rhel-server-7.4-x86_64-dvd_tempdir/custom-rhel-server-7.4-x86_64-dvd.20180305_112238.iso.sha256sum
Exiting using exit function.

The iso listed should match with the sha256 checksum in the smaller file.

Details of execution

At a high level the script performs the following steps:

1. Prompts the user for the name of the ISO to build from.
   • Or the system will take the name of the ISO from the command line.
2. The script verifies that the customization information in media_info exists for this ISO.
3. The ISO file is mounted at ${BUILDDIR}/isomount/ and the contents are extracted to ${BUILDDIR}/image/
   • These are gloval variables that can be customized.
   • See the Customization section below.
4. The customization information is loaded from the ./media_info/${ISONAME}.info.sh file
   • The file is a shell script format and sets variables used later in the make_iso.sh script.
   • Necessary variables are checked; the script exits if any are missing.
5. The various legacy and UEFI boot configuration files are updated
   • Values from the media_info files are used to update the files.
6. An ISO is built and stored in the ${BUILDDIR} directory.
   • The ISO begins with "custom-" and has the timestamp embedded in the name for tracking.

Customization

Script customizations

The make_iso.sh script has some global variables set at the top of the file that are necessary to configure for your specific build environment.

• BUILDROOT : This path is where the resulting ISO as well as the temporary files used during the customizatino process are stored.
• GOLDENISO : This is the path to the ISO files downloaded from the vendor, e.g. RedHat.com, etc.

Configuration files

The script relies on a number of ISO specific files to properly configure the final ISO correctly as new cutomized installation distributions are necessary. A knowledge of common Unix shell scripting tools such as awk, sed, rsync, and mkisofs.

The script first includes the variables setup within the media_info directory. The specific file that is included is based on the name of the ISO file chosen with the ".iso" removed. Each of these files defines these variables:

• SHA256SUM : (currently optional) The SHA256 checksum of the ISO image to enure the starting ISO is valid.
• DO_MBR and DO_UEFI : When set to 1, the script will configure the MBR and/or UEFI boot options.

Both of the MBR and UEFI seections use the same variables, differing only in their prefix (MBR_ or UEFI_). The following variables are prepended with either of these text strings replacing the X_.

• X_MENUFILE : This variable points to the text configuration file, normally the isolinux.cfg or grub.conf file that will be edited.

    MBR_MENUFILE="image/isolinux/isolinux.cfg"

• X_START : The string in this variable is a REGEXP search string

    MBR_START="^label linux"

• X_END : x

  MBR_END="append initrd=initrd.img"

• X_MENU : x

    MBR_MENU="label bootlocal
      localboot 0x80
      menu default

    label custom
      menu label Install ^Custom Red Hat Enterprise Linux 7.4
      kernel vmlinuz
      append initrd=initrd.img inst.stage2=hd:LABEL=${CDLABEL_FIXED} inst.ks=cdrom:/ks.cfg biosdevname=0 net.ifnames=0

    label linux
      menu label ^Install Red Hat Enterprise Linux 7.4
      kernel vmlinuz
      append initrd=initrd.img inst.stage2=hd:LABEL=RHEL-7.4\x20Server.x86_64 quiet
    "