**Contents** [[!toc levels=2]] # Introduction The purpose of this document is to guide you to create a [RAM disk](http://en.wikipedia.org/wiki/RAM_disk) image and a custom kernel in order to boot your mini NetBSD off a [Compact Flash](http://en.wikipedia.org/wiki/CompactFlash) or use it to debug it in an emulated environment, such as [qemu](http://en.wikipedia.org/wiki/QEMU). The ramdisk image will have to be inserted into your kernel and then extracted to memory of your embedded device (or your emulator) and used as the root file system, which then can be used by your kernel as if it resided on a "normal" storage media like a hard drive. The steps below were tested in a NetBSD 4.99.20 i386 box. # Create the ramdisk First we need to create the ramdisk that will get embedded into the kernel. The ramdisk contains a filesystem with whatever tools are needed, usually [[basics/init|init(8)]] and some tools like sysinst, ls(1), etc. ## Standard ramdisk To create the standard ramdisk (assuming your source tree lies at `/usr/src` and you have `/usr/obj` and `/usr/tools`): # cd /usr/src # ./build.sh -O ../obj -T ../tools -u tools # cd /usr/src/etc/ # make MAKEDEV # cd /usr/src/distrib/i386/ramdisks/ramdisk-big # make TOOLDIR=/usr/tools ## Custom ramdisk If you want to customize the contents of the filesystem, customize the `list` file. Let's say for example that we need the [[basics/uname|uname(1)]] utility to be included in the ramdisk, which is not by default. # cd /usr/src # ./build.sh -O ../obj -T ../tools -u tools # cd /usr/src/etc/ # make MAKEDEV # cd /usr/src/distrib/i386/ramdisks/ramdisk-big # cp list list.old Then we edit the `list` file, by adding the following line: PROG bin/uname And after having done it: # make TOOLDIR=/usr/tools Either way, you will get something like this: # create ramdisk-big/ramdisk-big.fs Calculated size of `ramdisk-big.fs.tmp': 5120000 bytes, 65 inodes Extent size set to 4096 ramdisk-big.fs.tmp: 4.9MB (10000 sectors) block size 4096, fragment size 512 using 1 cylinder groups of 4.88MB, 1250 blks, 96 inodes. super-block backups (for fsck -b #) at: 32, Populating `ramdisk-big.fs.tmp' Image `ramdisk-big.fs.tmp' complete And verify with: $ ls -lh ramdisk-big.fs -rwxr-xr-x 1 root wheel 4.9M Jun 19 08:33 ramdisk-big.fs # Build the kernel Next we shall build our custom kernel with ramdisk support. We may choose any INSTALL* kernel configuration. Here, we will use INSTALL_TINY: # cd /usr/src/sys/arch/i386/conf # cp INSTALL_TINY MY_INSTALL_TINY Then we edit `MY_INSTALL_TINY` file, and we go to the section: # Enable the hooks used for initializing the root memory-disk. options MEMORY_DISK_HOOKS options MEMORY_DISK_IS_ROOT # force root on memory disk options MEMORY_DISK_SERVER=0 # no userspace memory disk support options MEMORY_DISK_ROOT_SIZE=3100 # size of memory disk, in blocks The size of `MEMORY_DISK_ROOT_SIZE` must be equal or bigger than the size of your image. To calculate the kernel value you can use following rule: MEMORY_DISK_ROOT_SIZE=10000 would give 10000*512/1024 = 5000 kb We check that the following lines are un-commented: pseudo-device md 1 # memory disk device (ramdisk) file-system MFS # memory file system Once we are done with the configuration file, we proceed with building our kernel: # cd /usr/src # ./build.sh -O ../obj -T ../tools -u kernel=MY_INSTALL_TINY # Insert ramdisk to kernel Having built our kernel, we may now insert the ramdisk to the kernel itself: # cd /usr/src/distrib/i386/instkernel # cp Makefile Makefile.old Then we edit the `Makefile`, to make sure that the `RAMDISKS` and `MDSETTARGETS` variables are set properly. After the modifications, mine looks like this: # $NetBSD: how_to_create_bootable_netbsd_image.mdwn,v 1.3 2014/04/03 03:27:42 wiki Exp $ .include .include "${NETBSDSRCDIR}/distrib/common/Makefile.distrib" # create ${RAMDISK_*} variables # RAMDISKS= RAMDISK_B ramdisk-big .for V F in ${RAMDISKS} ${V}DIR!= cd ${.CURDIR}/../ramdisks/${F} && ${PRINTOBJDIR} ${V}= ${${V}DIR}/${F}.fs .endfor MDSETTARGETS= MY_INSTALL_TINY ${RAMDISK_B} - MDSET_RELEASEDIR= binary/kernel .include "${DISTRIBDIR}/common/Makefile.mdset" .include Next write: make KERNOBJDIR=/usr/obj/sys/arch/i386/compile TOOLDIR=/usr/tools Should you encounter errors of the following form, try increasing the `MEMORY_DISK_ROOT_SIZE` at your kernel configuration file. i386--netbsdelf-mdsetimage: fs image (5120000 bytes) too big for buffer (1587200 bytes) *** Error code 1 Provided that everything went ok, you will have the following files in your current directory: # ls -lh netbsd* -rwxr-xr-x 1 root wheel 21M Jun 20 11:07 netbsd-MY_INSTALL_TINY -rw-r--r-- 1 root wheel 1.5M Jun 20 11:07 netbsd-MY_INSTALL_TINY.gz -rw-r--r-- 1 root wheel 58K Jun 20 11:07 netbsd-MY_INSTALL_TINY.symbols.gz # Make image bootable Finally: # cd /usr/src/distrib/i386/floppies/bootfloppy-big # cp Makefile Makefile.old Edit the Makefile if your kernel config has a different name than INSTALL*. Replace `FLOPPYKERNEL= netbsd-INSTALL.gz` with `FLOPPYKERNEL= netbsd-MY_INSTALL_TINY.gz` (Where MY_INSTALL_TINY is of course the name of the custom kernel.) # make TOOLDIR=/usr/tools [...] Final result: -rw-r--r-- 1 root wheel 2949120 Jun 20 11:15 boot-big1.fs Now you are ready to test your image, with qemu for example: $ cd /usr/src/distrib/i386/floppies/bootfloppy-big $ qemu boot-big1.fs # Credits This article is based on [[Yazzy's]] work, who was kind enough to permit us include an article in this wiki. The original document may be found [here](http://www.yazzy.org/docs/NetBSD/netbsd-on-cf.txt). # Additional related links 1. [Creating a custom install/boot floppies for i386](http://www.netbsd.org/docs/guide/en/chap-misc.html#chap-misc-creating-bootfloppies)