[CentOS] How is initrd.img packed and compressed?

Wed Jan 31 19:46:53 UTC 2018
James Pearson <james-p at moving-picture.com>

Mircea Husz wrote:
> In order to work around a known upstream bug I needed to add a udev
> rule to pxeboot initrd.img on CentOS 7.
> The process is straightforward:
> 1 - extract the pxeboot initrd.img  to a new directory
> 2 - add the udev rule needed to fix the bug
> 3 - pack and compress it back in initrd.img format

Instead of re-creating a new initrd.img, why not just create an 
'updates' image that contains your new udev rule and use the 
'inst.updates=' pxeboot cmdline option?

I use this to add things to the install image - no need to alter the 
existing initrd image - if you need more info, let me know

James Pearson