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You accidentally deleted your production kernel?
Both your new and backup kernel are trash?

No worries. You could always use a FreeBSD setup or bootonly CD to load a fallback kernel from there.

It’s fairly easy to do so.

Just hit ‘6′ while in the beastie menu to enter the boot loader prompt.
Depending on your platform or installation, a plain “Hit [Enter] to boot immediatly…” prompt might be shown alternatively. Just press any key to enter boot loader prompt at this stage.

On the boot loader prompt, which shows up using the plain words ‘OK’ at the beginning of each line, enter this command:

OK set vfs.root.mountfrom=ufs:/dev/ad0s1a

This will force the kernel from the CD to use the root file system from the given location.
Replace the device name as required to match your system.

Then boot the system into single user mode like this:

OK boot -s

This should boot into your system useing the kernel from the CD-ROM.

If everything went smothely you will end up with a prompt like this:

[output omitted]
Mounting root from ufs:/dev/ad0s1a
Enter full pathname of shellor RETURN for /bin/sh:

Congratulations. You are now ready to go cleaning up your mess

On a Sun Ultra 5 keyboard and screen are used as default input/output devices. This causes the serial port not to be used by default, at least not unless you send a keypress over an attached terminal.

To change this behaviour, two values need to be changed in OpenBoot.

So first we need to enter OpenBoot by sending a Break over the serial line or STOP-A.

Examine the environment values like this and look out for the variables called ‘input-device’ and ‘output-device’:

# printenv
Variable Name Value Default Value
[output omitted]
output-device screen screen
input-device keyboard keyboard
[output omitted]

Set them as follows to enable the serial console to be used by default:

#setenv output-device virtual-console
#setenv input-device virtual-console

Next time the machine is powered on, the serial console should come up at once.

Building pxelinux and memdisk on FreeBSD is not as straight forward as on Linux. A fair amount of additional handwork is involved.

But don’t worry, all steps required to master this task are outlined below.

The requirement to build pxelinux came while implementing a FreeBSD-hosted network bootstrap environment, where I wanted to use it as primary boot loader.

Of course I could have taken pxelinux from an existing Linux distro’s binary package. I couldn’t resist the challenge however…

#1 Prerequisites

These prerequisite tools need to be installed first: nasm and gmake

It’s easiest you install them from the ports:

#cd /usr/ports/devel/gmake
#make clean build install && make clean
#cd /usr/ports/devel/nasm
#make clean build install && make clean

#2 Get the source

Since pxelinux and memdisk are part of syslinux, you need to fetch a current syslinux release tarball to a temporary directory and extract it.

#cd /tmp
#wget http://www.kernel.org/pub/linux/utils/boot/syslinux/syslinux-3.36.tar.bz2
#tar -xjpvf syslinux-3.36.tar.bz2

#3 Apply source code patch

Now you could run ‘gmake’ within the source directory, this would however yield a linker error.
Let’s fix this first.

#cd syslinux-3.36
#find . -type f -exec grep -le ‘elf_i386′ {} \; | xargs perl -i -p -e ’s/elf_i386/elf_i386_fbsd/g;’

#4 Building pxelinux and memdisk

Now let’s head on to building pxelinux and memdisk, the two components needed in particular.

#gmake pxelinux.bin
#cd memdisk; gmake; cd ..

They should compile cleanly so the next step would be copying them to your tftpd boot directory, which is /var/tftpd for me.

#cp pxelinux.bin /var/tftpd/pxelinux
#cp memdisk/memdisk /var/tftpd/memdisk

#5 Conclusion

pxelinux and memdisk can now be used in a pxe bootstrap environment (see also Convert FreeBSD ISO image for PXE bootstrap).

There still remain some compile time issues with syslinux itself. This is why running ‘gmake’ within the source directory yet fails due to unresolved include file dependencies.

I didn’t tamper with them because I was only interested in getting pxelinux and memdisk to run in the first place. Also I coulnd’t think of a practical reason in using syslinux on FreeBSD so I spared me these efforts.

Usually ISO’s of most Linux distros use isolinux as boot loader, so these may be served up easily for pxe bootstrap through pxelinux/memdisk.

For FreeBSD this does not hold true, so the vanilla ISO’s must be converted before they can be bootstrapped.

The basic idea is to convert the FreeBSD ISO into a harddisk image to circumvent a limitation in the ISO boot loader.

#1 Preparation

We need some staging directory where we can safely play around with the files.

#mkdir /tmp/build
#mkdir /tmp/build/iso.mnt
#mkdir /tmp/build/hd.mnt
#mkdir /tmp/build/mfs.mnt

#2 Get the ISO image

I usually use the ‘bootonly’ image because of it’s size (~25 MB). It would work with the full ISO’s of course, however will not only take longer to download via tftp but also require more memory on the client host.

#wget ftp://ftp.freebsd.org/pub/FreeBSD/ISO-IMAGES-i386/6.2/6.2-RELEASE-i386-bootonly.iso –output-document=/tmp/build/6.2-RELEASE-i386-bootonly.iso

Now we need to attach ‘md’ (memory device) to the ISO image and mount it.

#mdconfig -a -t vnode -f /tmp/build/6.2-RELEASE-i386-bootonly.iso
md0
#mount_cd9660 /dev/md0 /tmp/build/iso.mnt/

#3 Create a new harddisk image

Let’s create a new harddisk image of 32 MB in size. It make it a bit bigger than the original ISO so I could include further scripts with it.

#dd if=/dev/zero of=/tmp/build/6.2-RELEASE-i386-bootonly.hd bs=1m count=32
32+0 records in
32+0 records out
33554432 bytes transferred in 2.078232 secs (16145664 bytes/sec)

Then we attach a ‘md’ device to this one, too. Afterwards partition table and bsdlabel are initialized.

#mdconfig -a -t vnode -f /tmp/build/6.2-RELEASE-i386-bootonly.hd
md1
#fdisk -B -I /dev/md1
#bsdlabel -B -w /dev/md1

Now we would need to edit the bsdlabel to add the ‘a’ slice of type 4.2BSD covering the whole harddisk image.

#bsdlabel -e /dev/md1
# /dev/md1:
8 partitions:
# size offset fstype [fsize bsize bps/cpg]
a: 65520 16 4.2BSD
c: 65536 0 unused 0 0 # “raw” part, don’t edit

Finally, the slaved will be newfs’ed with UFS and mounted.
#newfs /dev/md1a
#mount /dev/md1a /tmp/build/hd.mnt

Now the ‘boot’ directory must be copied from the mounted ISO image onto the harddisk image.

#copy -r /tmp/build/iso.mnt/boot /tmp/build/hd.mnt/boot

#4 Optional: Prepare SysInstall for automatic installations

This step is completely optional, though will allow us to place an ‘install.cfg’ file to the image. SysInstall will use this file as configuration template for automatic installations. A sample of it is found within the source tree at /usr/src/usr.sbin/sysinstall/install.cfg. Optionally you can use mine as a starting point.

First we need to copy away mfsroot.gz into our build directory. It will then be extracted, attached to a vnode and mounted.

#cp /tmp/build/hd.mnt/boot/mfsroot.gz /tmp/build/hd.mnt
#gunzip /tmp/build/hd.mnt/mfsroot.gz
#mdconfig -a -t vnode -f /tmp/build/hd.mnt/mfsroot
md2
#mount /dev/md2 /tmp/build/mfs.mnt

Then add the install.cfg file to the mfsroot top level directory.

#cp /tmp/build/install.cfg /tmp/build/mfs.mnt

You are free to add further customizations, like self-built packages, to the mfsroot.
When finished unmount the mfsroot device, detach it from the ‘md’ device, compress and copy it back to the harddisk image.

#umount /tmp/build/mfs.mnt
#mdconfig -d -u 2
#gzip /tmp/build/mfsroot
#cp /tmp/build/mfsroot.gz /tmp/build/hd.mnt/boot

#5 Finalize

So let’s clean up little.

#umount /tmp/build/hd.mnt
#mdconfig -d -u 1
#umount /tmp/build/iso.mnt
#mdconfig -d -u 0

Let’s shift the harddisk image to the tftpd boot image directory, which is /var/tftpd/images for me.

#cp /tmp/build/6.2-RELEASE-i386-bootonly.hd /var/tftpd/images

Finally pxelinux must be instructed on how to boot this image.
The assistance of memdisk is required to achieve this by adding the lines below to pxelinux.cfg/default configuration file.

label fbsd62
kernel memdisk
append initrd=/images/6.2-RELEASE-i386-bootonly.hd harddisk

So from now on requesting ‘fbsd62′ at the pxelinux boot prompt should boot the image.

It happend to me occasionally that the FreeBSD boot loader crashed on some systems. So far this seems depending on the BIOS, because upgrading to the latest releases fixed it usually. I suspect that some BIOS versions mess up if a PXE bootstrapped image reports itself as beeing a harddisk.

It did not yet find a solution to this particular issue except using old-fashioned 1.44/2.88m floppy disk images for PXE bootstrap.

#6 Boot Environment and Configuration Files

This howto actually covers a topic which came up during development of a network installation environment.

The host acting as boot server is running FreeBSD with ISC dhpcd, stock tftpd and pxelinux serving as bootstrap loader.

I’m providing you with some basic configuration files to round up the picture.

My live-setup is in fact a bit more sophisticated than that and uses some additional scripting magic do achieve real automated setups not only for FreeBSD but also for various Linux distros. This however I am not allowed to publish in detail due to company policy.

dhcpd.conf

inetd.conf

pxelinux.cfg

install.cfg