[SATLUG] diskless ramdisk booting

Mark Mayfield mayfield_mark at gvtc.com
Thu Jul 21 14:00:04 CDT 2016


I didn't catch at first that your cramming you distro into the ramdisk 
instead of using an initial ramdisk. I put my whole systems on nfs 
shares and just loaded the kernel or kernel+initial ramdisk. The way he 
make the ramdisk your network drivers must be in the kernel

I would just go into the kernel drivers section->network cards and mark 
all the net drivers with * (in kernel) instead of M (kernel module)

I'd also use lsmod to find the kernel module the systems your using use 
and make sure they are options in the kernel. If they can't be compiled 
into the kernel you'll have to make sure they can be loaded from the 
ramdisk.

On 07/21/2016 08:53 AM, 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.
>
> Thanks, -Borries




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