Kickstart based RHEL installation from several ISO files on the one USB stick

Resolution

1. Create a usb_stick folder that will contain all the necessary files:

   # mount -o loop RHEL-7.6-20181010.0-Server-x86_64-boot.iso /media/
   $ mkdir usb_stick
   $ cp -a /media/isolinux/ usb_stick
   $ chmod -R u+w usb_stick
   

2. Copy all the required RHEL ISO files to the usb_stick, for example:

   $ ll usb_stick/*.iso
   total 12360716
   -rw-rw-r-- 1 test test 4203741184 Oct 30 14:33 RHEL-7.0-20140507.0-Workstation-x86_64-dvd1.iso
   -rw-rw-r-- 1 test test 4497342464 May 13 13:51 RHEL-7.6-20181010.0-Server-x86_64-dvd1.iso
   -rw-rw-r-- 1 test test 3956277248 Oct 30 14:43 RHEL-7.7-20190723.1-Client-x86_64-dvd1.iso
   

3. Add menu items to the usb_stick/isolinux/isolinux.cfg in order to install the corresponding RHEL:

   ...
   label server
     menu label Install Red Hat Enterprise Linux 7.6 ^Server
     menu default
     kernel vmlinuz
     append initrd=initrd.img inst.ks=hd:LABEL=RHEL7:/server.cfg inst.stage2=hd:LABEL=RHEL7:/RHEL-7.6-20181010.0-Server-x86_64-dvd1.iso
   
   label netinstall
     menu label Install Red Hat Enterprise Linux 7.6 ^Netinstall Server
     kernel vmlinuz
     append initrd=initrd.img inst.ks=hd:LABEL=RHEL7:/netinstall.cfg inst.stage2=hd:LABEL=RHEL7:/RHEL-7.6-20181010.0-Server-x86_64-dvd1.iso
   
   label client
     menu label Install Red Hat Enterprise Linux 7.7 ^Client
     kernel vmlinuz
     append initrd=initrd.img inst.ks=hd:LABEL=RHEL7:/client.cfg inst.stage2=hd:LABEL=RHEL7:/RHEL-7.7-20190723.1-Client-x86_64-dvd1.iso
   
   label desktop
     menu label Install Red Hat Enterprise Linux 7.0 ^Workstation
     kernel vmlinuz
     append initrd=initrd.img inst.ks=hd:LABEL=RHEL7:/workstation.cfg inst.stage2=hd:LABEL=RHEL7:/RHEL-7.0-20140507.0-Workstation-x86_64-dvd1.iso
   ...
   

4. Create the appropriate kickstart files (for example usb_stick/minimal.cfg):

   # RHEL7
   lang en_US
   keyboard us
   timezone Europe/Prague --isUtc
   rootpw a
   #platform x86, AMD64, or Intel EM64T
   reboot
   text
   bootloader --location=mbr --append="crashkernel=auto"
   zerombr
   clearpart --all --initlabel
   autopart
   auth --passalgo=sha512 --useshadow
   firewall --enabled
   firstboot --disable
   network  --bootproto=dhcp --onboot=on --ipv6=auto --hostname=test
   
   %packages
   @base
   %end
   

   The folder for the USB stick contains the following files:

   $ ll usb_stick/
   total 44
   drwxrwxr-x 4 test test 4096 Oct 30 15:26 .
   drwxrwxr-x 5 test test 4096 Oct 30 15:05 ..
   -rw-r--r-- 1 test test  426 Oct 30 14:48 client.cfg
   drwxr-xr-x 2 test test 4096 Oct 30 15:11 isolinux
   -rw-r--r-- 1 test test  426 Oct 30 14:48 netinstall.cfg
   -rw-r--r-- 1 test test  426 Oct 30 14:47 server.cfg
   -rw-r--r-- 1 test test  426 Oct 30 14:48 workstation.cfg
   -rw-rw-r-- 1 test test 4203741184 Oct 30 14:33 RHEL-7.0-20140507.0-Workstation-x86_64-dvd1.iso
   -rw-rw-r-- 1 test test 4497342464 May 13 13:51 RHEL-7.6-20181010.0-Server-x86_64-dvd1.iso
   -rw-rw-r-- 1 test test 3956277248 Oct 30 14:43 RHEL-7.7-20190723.1-Client-x86_64-dvd1.iso
   

5. Create the ISO image (the command isohybrid makes USB stick bootable):

   #!/bin/bash
   
   ISO=usb_stick
   NAME="RHEL7"
   
   mkisofs -allow-limited-size -o $ISO.iso \
       -b isolinux/isolinux.bin -c isolinux/boot.cat -no-emul-boot -V "$NAME" \
       -boot-load-size 4 -boot-info-table -r -T -J $ISO
   isohybrid -v $ISO.iso
   

6. Copy the usb_stick.iso to physical USB stick:

   # dd if=usb_stick.iso of=/dev/<USB stick device name> bs=512k; sync
   

   or

   # cat usb_stick.iso > /dev/<USB stick device name>
   

Disclaimer: Using custom ISO images is not supported; for example if anaconda fails when using a custom ISO image, Red Hat will not be able to help investigate the issue.