All I want do to is to install netbsd on flash memory and mount root and 
other fs as read only; only fs like /var or /tmp should be writable and I 
need to create ramdisk in memory for those devices (it is a bad things to 
write on flash for tmp files or logs).

And I do not have any swap partition on disk to use the command mount_mfs.
So I need pure ramdisk.

I'll try to understand the mechanism in "/usr/src/distrib/i386/floppies" as 
you suggested.

Thanks,
Roberto

--On Friday, May 16, 2003 10:27:52 -0500 Frederick Bruckman 
<fredb@immanent.net> wrote:

> On Fri, 16 May 2003 roberto@redix.it wrote:
>
>> I'd like to setup several memory disk (ramdisk), but I did not find any
>> helpful info on the docs (sorry).
>> I'd like to know:
>>  - what are the kernel options to enable ramdisk?;
>>  - which are device files I need?;
>
> The ramdisk needs "pseudo-device md 1" (or > 1), and "/dev/md0a"  and
> "/dev/md0d" for one ramdisk; you could do "cd /dev; sh MAKEDEV md1" to
> support a second (and so on).
>
>>  - what command to create, mk file sys. and mount?
>>
>> P.S.: All I've found is for FreeBsd but seems to me inapplicable to
>> NetBsd: mknod /dev/ad0a c 116 0
>>  mknod /dev/ad0c c 116 2
>>  disklabel -e /dev/ad0c and define a partition a: type 4.2BSD
>>  disklabel -B -r /dev/ad0c
>>  newfs /dev/ad0a
>>  mount /dev/ad0a /memory_fs
>
> The "/dev/MAKEDEV" script does the first two steps (or not, if you
> only need one ramdisk), then you'd need to run "mdconfig(8)". (See
> also "md(4)".) The rest should be about the same. I've never tried it.
>
> The release build uses "makefs(8)" and "mdsetimage(8)" to create a
> file system image and install it into the kernel, which is how the
> install disks manage to boot from a ramdisk. If that's what you're
> trying to do -- make a bootable image -- you might be able to usurp
> the release building mechanism in "/usr/src/distrib/i386/floppies".
>
> Frederick
>