pxeboot - EXT3-fs:unable to read superblock

Steve steve at focb.co.nz
Wed Jun 16 23:20:45 UTC 2004


On Wed, 16 Jun 2004, Grey Kuyper wrote:

> Steve:
>  
> It is trying to mount a remote NFS.
> The HDD had NOT beed disconnected.
> I disconnected the HDD and rebooted. There is no change in behaviour.
>  
> I also did the following:
>  
> 1) I created a /nfs subdirectory on the server.
> 2) I copied the ENTIRE contents of the client's / directory to the server's /nfs directory.
> 3) here are the contents of the /etc/exports file:
>      /nfs      192.168.0.100(ro,no_root_squash,sync)
> 4) I restarted the nfd daemon with service nfs restart.
> 5) I added root=/nfs to the append line in the /tftpdboot/pxelinux.cfg/default file. The complete line now reads:
>      APPEND initrd=initrd-2.4.20-6.img root=/nfs
>  
> To me this should export the server's /nfs as a point to mount on the client. It should be identical to what the client sees when it boots from its own hard disk (since it is a copy of that hard disc that has beed placed inn  the /nfs directory of the server and then exported via nfs)
> 
> This did change the error message. It now says:
>  
>    VFS: Cannot open root device "/nfs" or 00:00
>    please append a correct "root=" boot option.
>  
> I guess this is progress!  I just read a half a dozen posts on the internet re this message but nothing usable yet.
> 

with nfs usually the mount is specified as server:/mountpoint (if my 
memory serves me correctly, its been a while since I played with nfs)

specifying /nfs as the root device will mean that the kernel will look for 
a device called "/nfs" and assume that this is a block capable device and 
try to mount it - as you dont even have a hard drive, it wont be able to 
find this device (in the initrd image) and so will fail with this error.

(co-incedently, this is how initrd mounts local hard drives and scsi 
devices)

You will need to bring up the nfs subsystem on bootup which shoudl be done 
by the rc script in the initrd, modules for your netowkr devices, nfs 
stuff and possibly nfs utils such as the portmapper may need to be brought 
up within the initrd ramdisk and then the nfs share mounted as a rood 
device after your system has become nfs aware.

Keep in mind that I've never done this myself - but the boot sequences 
tend to be a logical system and before you can mount an nfs device your 
system will need the necessary nfs support - and the locical place for 
that to be brought up is the initrd ramdisk.



-- 
Steve.





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