Before you can use initrd, both RAM
disk support (CONFIG_BLK_DEV_RAM=y) and initial RAM disk support
(CONFIG_BLK_DEV_INITRD=y) must be compiled into the Linux kernel.
Then you need to prepare the normal root filesystem and create the RAM
disk image. Your Linux distribution may have utilities to do some of
the setup for you; for example, the Red Hat distribution comes with
the
mkinitrd command, which builds
the initrd image. For detailed
information, see the initrd manpage
and the file initrd.txt (the path may vary but is
usually something like
/usr/src/linux/Documentation/initrd.txt).
Once your Linux system has been set up for initrd, you can do one of the following,
depending on which boot loader you are using:
If LILO is your boot loader, add the initrd option to the appropriate image section:
image = /vmlinuz
initrd = /boot/initrd # The file to load as the contents of /dev/initrd
...
Run the /sbin/lilo command, and you
can reboot with initrd.
If you are using Loadlin, add the initrd option to the command line:
loadlin c:\linux\vmlinuz initrd=c:\linux\initrd
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4.5. Boot-time Kernel Options |  | 5. Red Hat and Debian Package Managers |