I am trying to boot a ramdisk and am getting the following error:
16384 ram0 (driver?)
.
.
.
16384 ram181 (driver?)
No filesystem could mount root, tried:ext2 iso9660.
Kernel panic - not syncing:VFS:Unable to mount root fs on unknown-block (1,0)

This is RHEL5 so input the ramdisk_blocksize into isolinux.cfg:
DEFAULT linux
LABEL linux
KERNEL vmlinuz
APPEND initrd=initrd.img root=/dev/ram0 ramdisk_blocksize=1024 ramdisk=2969600 rw init=/etc/rc.d/rc.sysinit


#!/bin/sh
mkdir /mnt/ramdisk

echo Cleaning up...
rm -f /Build/BOS/image/*; sync
rm -f /Build/BOS/tmp/ram0; sync

echo Generating zeroed ext2 fs...
dd if=/dev/zero of=/Build/BOS/tmp/ram0 bs=1024 count=2969600 >& /dev/null; sync
mke2fs -F -L / -b 1024 -m 0 /Build/BOS/tmp/ram0 2969600 >& /dev/null
echo Mounting new fs...
mount -t ext2 -o loop /Build/BOS/tmp/ram0 /mnt/ramdisk
sync
echo Copying dependencies to fs...
pushd /mnt/ramdisk
cp -dpR /Build/BOS/POOL/* /mnt/ramdisk
popd
sync
echo Configuring library dependencies...
ldconfig -r /mnt/ramdisk; sync
echo Unmounting new fs...
umount /mnt/ramdisk
echo Creating compressed RAM disk image...
gzip -9 /Build/Recorder-BOS/tmp/ram0
sync
mv /Build/BOS/tmp/ram0.gz /Build/BOS/isolinux/initrd


I updated the fstab and mtab files :
fstab:
/dev/ram0 / ext2 defaults 0 0

mtab:
/dev/ram0 / ext2 rw 0 0

I updated the kernel to support 182 ramdisks. Any ideas why this is failing?

When you mean ramdisk you mean a dedicated device that should hold the data at reboot or do you mean a normal ramdisk that erases all data on reboot?

normal ramdisk that erases all data on reboot. This system does not have a hard drive. The messages scroll by so fast that I can not tell if there are any errors before the 182 16384 ram0-182 (driver?) scroll by and it ends in Panic.

I am not sure I have ever heard of someone trying to boot to a ram disk like that.

You'd have to create it, format it and load the data to it before almost anything was loaded or configured. To even run a script you'd have to be up in linux. I guess you could then use loadlin or such to change command control to the ram disk.

You might be able to create it with memdisk and pxe or gpxe boot.

I have been told that I have boot with a DVD. I boot ramdisks all the time with flash drives (Lilo) and PXEBoots. It is just not working with isolinux. I will look into memdisk.

Then I might be misunderstanding the exact thing you are trying to do. It seems like you wanted a computer to boot from cold boot to a ram drive without pxe or flash drive with option toram.

Since isolinux is very similar to pxe, both syslinux products, I believe it should work. I am trying to replicate what slackware does with their busybox ramdisk.
Slackware isolinux.cfg file:
default hugesmp.s
prompt 1
timeout 1200
display message.txt
F1 message.txt
F2 f2.txt
label huge.s
kernel /kernels/huge.s/bzImage
append initrd=initrd.img load_ramdisk=1 prompt_ramdisk=0 rw SLACK_KERNEL=huge.s
label hugesmp.s
kernel /kernels/hugesmp.s/bzImage
append initrd=initrd.img load_ramdisk=1 prompt_ramdisk=0 rw SLACK_KERNEL=hugesmp.s
label speakup.s
kernel /kernels/speakup.s/bzImage
append initrd=initrd.img load_ramdisk=1 prompt_ramdisk=0 rw SLACK_KERNEL=speakup.s

I think I have found the problem. but will not able to test until tomorrow. I thought the kernel would create the ram0... devices dynamically. I am going to try and add the devices to ramdisk to see if that helps.

I think then the issue is that some machines need isolinux while others can use syslinux.

The system is booting from the DVD now. I change to a 64 bit version of the 2.6.25.14 kernel based on the Redhat 2.6.18 X64 config. The 32 bit version of the 2.6.25.14 was based on the RedHat 2.6.18 32bit config, so I am not sure what is different about the two kernels. I did a diff on the config files, but the amount of differences was huge.

All is working now under the 64 bit version of the 2.6.25.14 kernel. Using extlinux 4.0 for the flash drive version and isolinux for the DVD version. Still not sure what option was kernel option in the 32 bit version was missing to cause it to fail like that.

your append file doesn't state ramdisk_size=2048000 or whatever size...you only wrote ramdisk=20xxxx

try this

#create 'ramdisksave' directory using terminal
mkdir /home/ramdisksave

#edit grub config or custom_40. This allocates max ram for ramdisks
kernel /vmlinuz ramdisk_size=2048000

#edit rc.local add these lines to create & mount ramdisk at boot
mke2fs -t ext2 /dev/ram1 2048000
mount /dev/ram1 /home/ramdisksave

#copies 'ramdisksave' contents to ramdisk save as *.sh make exe!
cp -a /home/ramdisksave/. /mnt/ram1

#saves ramdisk contents to ramdisksave folder save as *.sh make exe!
cp -a /mnt/ram1/. /home/ramdisksave/

#deletes ramdisk contents save as *.sh make exe!
cd /mnt && rm -rf ram1/*

#deletes ramdisksave contents save as *.sh make exe! DANGEROUS!!
cd /home && rm -rf ramdisksave/*