# "Cannot open root device" when booting from PXE

## elomaniak

Hi Folks i finally managed to get the kernel loading for my PXE Boot experiment/research

I am now getting a kernel panic while booting

here's the exact message

```
 VFS: Cannot open root device "nfs" or unknown block (0,255)

please append a correct "root=" boot option; hera are the available options

Kernel panic - not syncing VFS: unable to mount root fs on unknown block (0,255)

```

heres my /diskless/pxelinux.cfg/default

```

DEFAULT    Ubuntu test

LABEL      Ubuntu test

      kernel /client1/ubuntu/casper/vmlinuz

      append root=/dev/nfs nfsroot=192.168.0.1:/diskless/client1/ubuntu ip=dhcp

      initrd=/diskless/client1/ubuntu/initrd.lz quiet splash --

```

fstab

```

# <fs>               <mountpoint>   <type>      <opts>   <dump/pass>

/dev/sda1            /      reiserfs   noatime0 1

#/dev/SWAP            none      swap      sw   0 0

/dev/sr0            /mnt/cdrom   auto      noauto,ro   0 0

/diskless/ubuntu.iso         /diskless/client1/ubuntu   auto   defaults,loop,user   0 0

```

/etc/exports

```
# /etc/exports: NFS file systems being exported.  See exports(5).

/diskless/client1/ubuntu/ *(ro,sync,no_wdelay,insecure_locks,no_root_squash,insecure)

```

for me it seems to be ok, I am trying to figure it our for about two hours without any luck

maybe someone can suggest something that might help

Thanks in advance

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## honp

Can your kernel do this?

- NFS filesystem support (CONFIG_NFS_FS).

- Root file system on NFS (CONFIG_ROOT_NFS).

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## elomaniak

CONFIG_NFS_FS=m

cant find CONFIG_ROOT_NFS in my .config

EDIT: found it, dependencies showed i had to build in CONFIG_NFS_FS=y

will check and report later

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## honp

Yes, modul is not enough, or you must use initrd somehow...

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