Building bootable FreeBSD/i386 images
From time to time I hear people complain at how hard it is to build an image from the FreeBSD sources. This week, I'll explain how I built a bootable i386 image on a USB flash device and also make some observations about the results.
Recently, I needed to create a bootable i386 image. The easiest way was to build one on my amd64. Here's what I did. I setup my environment for the build (steps 1-3), built FreeBSD/i386 userland and kernel (steps 4 and 5), prepared the flash (steps 6-11), installed userland and the kernel (steps 12 and 13), added the extra files needed for boot (steps 14-18). The detailed commands follow:
setenv MAKEOBJDIRPREFIX /blah
setenv TARGET i386
setenv TARGET_ARCH i386
make buildworld
make buildkernel KERNCONF=GENERIC
fdisk -I da0
fdisk -B da0
bsdlabel -w da0s1 auto
bsdlabel -B da0s1
newfs /dev/da0s1a
mount /dev/da0s1a /mnt
make installworld DESTDIR=/mnt
make installkernel DESTDIR=/mnt KERNCONF=GENERIC INSTALL_NODEBUG=t
make distrib-dirs DESTDIR=/mnt
make distribution DESTDIR=/mnt
echo /dev/da0s1a / ufs rw 1 1 > /mnt/etc/fstab
echo ifconfig_DEFAULT=DHCP > /mnt/etc/rc.conf
echo hostname=demo >> /mnt/etc/rc.conf
I put all this on an SD card and inserted that into an usb adapater and booted the laptop with it. FreeBSD's base system isn't too big these days, only 205MB for a full system.
% df /mnt
Filesystem 1024-blocks Used Avail Capacity Mounted on
/dev/da0s1a 484822 205570 240468 46% /mnt
This can easily be trimmed, but with a 512MB SD card for $5 at Office Max, there's little point in trimming for the project I needed the flash for. I just needed something that I could boot to transition my FreeBSD/amd64 laptop to a FreeBSD/i386 laptop.
If one needed to reduce the amount of space used by an installation, then there's a number of options than can be used to reduce the footprint of the system. In my experience, it is best to build everything without these options, then use the WITHOUT_* options on the installworld step to keep the image size down. It is easy to cut FreeBSD's footprint in half with these options. In addition, the kernel is 28MB with all its modules, and this can easily be reduced below 5MB in most cases.
nanobsd can be used to automate this process, as can TinyBSD. I'll save for another column the techniques I have used in the past to reach 16MB.
Posted by Warner Losh
at 11:46 PM
9 comments:
Destari said...
Also, in many cases, removable devices can boot with a different device name than it did originally. For instance, it may come up as da0, or da1, or daX, sometimes even adX (think: virtual machines).
In these cases, I label my UFS file system while doing the newfs command with the -L option:
newfs -L "usbroot" /dev/...
or something similar. Then, instead of using /dev/daXXX in the /etc/fstab, I use:
/dev/ufs/usbroot ...
and I also make sure I add GEOM_LABEL into my kernel config (or load as a module). It's relatively small, and very useful.
