It seem like CentOS7/RHEL7 is slightly different from CentOS6/RHEL6, when trying to install from USB with multiple boot images (eg YUMI).
CentOS7/RHEL7 require “inst.stage2″^^1 to be specific, and the default from the ISO file is “inst.stage2=hd:LABEL=CentOS\x207\x20x86_64” or “inst.stage2=hd:LABEL=RHEL-7.3\x20x86_64”. This will need to be amend to reflect the correct LABEL of the usb.
How to find out the LABEL for your USB? You can refer to here. But to save your time (since you found this instead of that):
1. Boot into Linux
2. Assume your USB is on /dev/sda, and the first partition contain your multiboot:
Example of the label on my USB is “MULTIBOOT”, therefore I need to change the “inst.stage2” to:
which will load the stage2 image from /dev/sda1/multiboot/CentOS-7
^^1 – This specifies the location to fetch only the installer runtime image; packages will be ignored.
^^2 – More info on the Boot options from here.