CentOS - Feb 2009 - Problem with PXEBOOT of diskless client -- fails to mount RAMDISK

I am having a problem with setting up diskless clients under CentOS 5.2.
I have everything working under CentOS 4.7.  This is an adaptation of
the (somewhat old) Diskless Linux with PXE HOWTO by Gerd v. Egidy,
originally at the URL
http://www.intra2net.com/opensource/diskless-howto/, which is now defunt
(there is a mirror of it at
http://blog.chinaunix.net/u/2389/showart_82438.html). 

What I am doing is using a RAMDISK to mount a NFS exported (read-only)
root file system and copying part of it to a RAMDISK root file system,
all of this after configuring the clients ethernet (via DHCP) and
loading the NFS modules.  The RAMDISK uses a statically built BusyBox
for all of its functions, including ash.

I am using the stock syslinux, dhcpd, tftp-server, and kernel RPMS.

My /tftpboot directory contains:

sauron.deepsoft.com% dir -l /CentOS52/tftpboot/
total 10012
-rw-r--r--  1 root root 8388608 Feb 12 14:26 pxeboot-2.6.18-92.el5.img
-rw-r--r--  1 root root   13148 Feb 11 16:27 pxelinux.0
drwxr-xr-x  2 root root    4096 Feb 12 14:37 pxelinux.cfg/
-rw-r--r--  1 root root 1806388 Feb 11 16:26 vmlinuz-2.6.18-92.el5
sauron.deepsoft.com% dir -lhR /CentOS52/tftpboot/
/CentOS52/tftpboot/:
total 9.8M
-rw-r--r--  1 root root 8.0M Feb 12 14:26 pxeboot-2.6.18-92.el5.img
-rw-r--r--  1 root root  13K Feb 11 16:27 pxelinux.0
drwxr-xr-x  2 root root 4.0K Feb 12 14:37 pxelinux.cfg/
-rw-r--r--  1 root root 1.8M Feb 11 16:26 vmlinuz-2.6.18-92.el5

/CentOS52/tftpboot/pxelinux.cfg:
total 16K
-rw-r--r--  1 root root 101 Feb 12 14:37 default
-rw-r--r--  1 root root 134 Feb 12 14:09 default~

and /CentOS52/tftpboot/pxelinux.cfg/default contains:

sauron.deepsoft.com% cat /CentOS52/tftpboot/pxelinux.cfg/default
LABEL linux
        KERNEL vmlinuz-2.6.18-92.el5
        APPEND ramdisk_size=8192 initrd=pxeboot-2.6.18-92.el5.img

vmlinuz-2.6.18-92.el5 is the stock kernel, copied from /boot

pxeboot-2.6.18-92.el5.img is a 8meg EXT2 filesystem image (under CentOS
4.7 the image is compressed, under CentOS 5.2, I have it uncompressed --
I seem to get 'further' that way).

The last thing the kernel writes out is:

RAMDISK: ext2 filesystem found at block 0
RAMDISK: Loading 8192KiB [1 disk] into ram disk... done.
EXT2 fs: blocksize too small for device.
grow_buffers: requested out-of-range block 18446744071562067968 for device ram0
isofs_fill_super: bread failed, dev=ram0, iso_blknum=17, block=-2147483648
No filesystem could mount root, tried: ext2 iso9660
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(8,3)

Under CentOS 4.7 (*stock* kernel version 2.6.9-67.0.22.EL), the ramdisk
is uncompress, mounted, and the linuxrc script runs.  Once the root file
system is NFS mounted and setup, the normal boot process continues to
completion. *Something* seems to be different with CentOS 5.2, and
things don't seem to work and I cannot figure it out. I've looked
through all of the kernel documents, but I am not finding any clues.


-- 
Robert Heller             -- 978-544-6933
Deepwoods Software        -- Download the Model Railroad System
http://www.deepsoft.com/  -- Binaries for Linux and MS-Windows
heller at deepsoft.com       -- http://www.deepsoft.com/ModelRailroadSystem/

> -----Original Message-----
> From: centos-bounces at centos.org 
> [mailto:centos-bounces at centos.org] On Behalf Of Robert Heller
> Sent: Thursday, February 12, 2009 5:15 PM
> To: centos at centos.org
> Subject: [CentOS] Problem with PXEBOOT of diskless client -- 
> fails to mountRAMDISK
> 
> sauron.deepsoft.com% cat /CentOS52/tftpboot/pxelinux.cfg/default
> LABEL linux
>         KERNEL vmlinuz-2.6.18-92.el5
>         APPEND ramdisk_size=8192 initrd=pxeboot-2.6.18-92.el5.img
> 
-------
Try changing your RAM Disk Size above to 16384 and give that a go.

JohnStanley

On Thu, Feb 12, 2009 at 05:14:54PM -0500, Robert Heller
wrote:
> I am having a problem with setting up diskless clients under CentOS 5.2.
> I have everything working under CentOS 4.7.
...
> 
> RAMDISK: ext2 filesystem found at block 0
> RAMDISK: Loading 8192KiB [1 disk] into ram disk... done.
> EXT2 fs: blocksize too small for device.
/boot/config-2.6.18-*.el5 reads:
...
CONFIG_BLK_DEV_RAM_BLOCKSIZE=4096
...
your ext2 filesystem is using 1024...

append ramdisk_blocksize=1024 to your command line?

What about adding your howto to the centos wiki?

Cheers,

Tru
-- 
Tru Huynh (mirrors, CentOS-3 i386/x86_64 Package Maintenance)
http://pgp.mit.edu:11371/pks/lookup?op=get&search=0xBEFA581B
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