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Old 10-10-2011, 08:45 PM   #1
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diskless node unable to mount root FS via NFS

Hello! I'm using TFTP, NFS and DHCP to boot a diskless node using PXELinux.

Each node has a basic root filesystem which resides in
/diskless/ip_address on the server

Right now, my node acquires an IP from my DHCP server, which instructs the bootrom to download a file called pxelinux.0, and the default pxelinux config file (/diskless/pxelinux.conf/default ) is shown below:

DEFAULT /bzImage
APPEND ip=dhcp root=/dev/nfs nfsroot=
The node downloads the bzImage via tftp (INTFTPD_PATH="/diskless") and boots the kernel. It goes through its hardware detection and all that fun stuff, and then the message:

VFS: cannot open root device "nfs" or unknown block(2,0)
The root device that it is refering to "nfs" is that which is defined in the pxelinux default config as root = /dev/nfs

[NOTE: Modern kernels recognize root=/dev/nfs as a command-line argument] Which leads me to think that I am possibly missing something in the kernel (bzImage) that the client node is booting. Here is a grep NFS of the kernel .config file:

# CONFIG_NFS_V4_1 is not set
# CONFIG_NFSD_V3_ACL is not set
# CONFIG_NFSD_V4 is not set
From what I can see, everything is enabled that needs to be enabled. Maybe a missing kernel option isn't the answer.

ANY suggestions would be awesome!

Last edited by jwpaine; 10-10-2011 at 08:48 PM.
Old 10-11-2011, 04:58 PM   #2
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I don't think defining a mountpoint in the /dev tree is a great idea. Try a different mountpoint. I assume you plan to do a pivotroot after the NFS mount happens, otherwise I think you have to mount the NFS share on '/'.

--- rod.
Old 10-11-2011, 08:00 PM   #3
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No. root=/dev/nfs does not point to a specific device. "/dev/nfs" is an argument that is read by the kernel, before opening a root FS via NFS.

The problem was the kernel on my Gentoo server had been configured for NFS version 2 server support, when my client was using 3.0, so a little change and now my diskless node is booting up and providing a login prompt.

Thanks anyways, though.


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