[SATLUG] diskless ramdisk booting

Borries Demeler demeler at biochem.uthscsa.edu
Thu Jul 21 11:42:23 CDT 2016


On Thu, Jul 21, 2016 at 10:55:29AM -0500, Bruce Dubbs wrote:
> 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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Thanks, Bruce, we'll check it out. 

-b.


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