[SATLUG] diskless ramdisk booting

Bruce Dubbs bruce.dubbs at gmail.com
Thu Jul 21 10:55:29 CDT 2016


Borries Demeler wrote:
> I am hoping someone on this list can explain how diskless booting works.
>
> I have a bunch of high school kids in my lab this summer and we are
> trying to build a diskless linux cluster as a summer project. I have a
> bunch of generic boxes with quad-core processors, on board video and 8
> GB RAM each. We configured one of the boxes with CentOS 6.8 as a head
> node. It has dhcpd, tftpd, nfs working fine now.  We can successfully
> pxe boot various iso images served through the tftp server, the nodes
> get private IP addresses, tftp boot the kernels and ramdisks on the iso
> images, and the nodes can mount nfs shared volumes from the head node.
> All of this works fine.
>
> We now wanted to build our own custom image and wanted to compile a
> minimal kernel and build a minimal ramdisk on which we could nfs mount
> various shares that hold the software and home directories we want to have
> accessible on the slave nodes.
>
> But we so far have been unable to build a proper kernel or ramdisk that
> gets past the mounting point where the root ramdisk file system gets
> mounted and cannot figure out where we are going wrong. Any help would
> be appreciated. We tried to follow this guide to the T:
>
> http://eduardo-lago.blogspot.com/2012/06/ram-only-pxe-boot-smallest-diskless.html
>
> and searched the internet for all kinds of other documentation on the topic.
> But we must be missing something essential, like our init is not getting
> executed or the kernel cannot find the root file system.
>
> Any help for these kids would be greatly appreciated! Can someone explain
> how the boot process works exactly step-by-step so we can see where our
> newly built image might be failing? THe boot process always fails at the
> point where the initrd specified ramdisk does not mount root.

Have you made a custom initrd?  See if

http://www.linuxfromscratch.org/blfs/view/stable/postlfs/initramfs.html

helps.  You will, of course, need to modify the init.in file.

   -- Bruce



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