OpenBSD LiveUSB

[Oko]

Can anybody share with me (jggimi you come first to my mind) your experience in creating LiveUSB image of the OpenBSD. I Google little bit and I saw how to on OpenBSD wiki pages. Without careful inspection I am concern that the described process doesn't take into account that USB stick is writable media unlike LIveCD. In another words 8Gb LiveUSB should be nothing else but removable SCSI hard drive. I want to be able
to add and remove packages and have 2GB of home space.

I also saw that Jacek Artymiak is selling LiveUSB images of OpenBSD for something like 50 euros. Since he is very credible person I would imagine that LiveUSB image is not that difficult to create.

Would a simple installation on the machine to which USB is attached before the boot work as long as I select SCSI drive instead regular HDD?

I saw howtos for NetBSD and FreeBSD on line. OpenBSD should not be to different than NetBSD.

Jggimi can you tell me little bit about those kernel changes in OpenBSD 4.5 which are making creating LiveCD easier?

Finally, it looks also that I could use BoulFish
http://www.kernel-panic.it/software/bowlfish/
script can be used. Any thoughts on that one?

[jggimi]

USB mass storage is managed through sd(4). It is a virtual SCSI device, no matter if the device is flash memory or hard drive.

You can do a standard installation to any USB device, as long as it has sufficient capacity. Since it is treated as a hard drive, use an MBR on architectures that require them, as well as a standard disklabel.

If your BIOS permits booting from USB, nothing else is needed.

If your BIOS does not permit booting from USB, you just need a boot loader on some other media, such as: diskette, optical disc, or network.

The only changes I've made to LiveCD kernels are to point the root partition to cd0a. This is no longer necessary with 4.5, and is entirely unnecessary with sd devices. The major changes for read-only (live) media are not kernel. The changes, instead, are to /etc/rc. In general, one mounts a set of MFS filesystems for read/write.

Modern flash media is supposed to have good write lifespan, therefore, with modern BIOS and modern USB devices, the general recommendation is to treat your stick like a disk drive, and not worry.

Since most modern sticks are much larger than the storage used in tiny embedded systems, I don't think bowlfish is necessary. It's hard to find USB sticks with less than 1/2 GB of storage these days, and a complete i386 or amd64 system will fit in that with room to spare.

[BSDfan666]

Adding to jggimi's informative post, one problem you might encounter is geometry related.

When a system boots from USB, the BIOS will emulate a hard drive temporarily for real mode disk access.. this allows the MBR and the PBR code to read and write from/to the USB mass storage device.

Sometimes this emulated device will have geometry that's different from what was determined via the umass/sd(4) probing, the side effect is the second stage loader cannot find /boot on some systems. (..you'll likely see "ERR M" if this is the case).

I've only witnessed this on some older systems, but you might scratch your head wondering why the device boots on some systems.. but not others.

Hope that helps.

[ocicat]

Originally Posted by BSDfan666

Sometimes this emulated device will have geometry that's different from what was determined via the umass/sd(4) probing, the side effect is the second stage loader cannot find /boot on some systems. (..you'll likely see "ERR M" if this is the case).

As an anecdote, I have seen this when developing an application to clone disks on Sun hardware which expects all partitions to be aligned on cylinder boundaries. When attempting to use dump(8) & restore(8) on an identical disk which was attached via USB, I still had to massage where partitions were located such that they could later be mounted; a straight bit-by-bit copy (even using dd(1)...) would lead to incorrect results because the sd(4) interface exposes a different geometry than wd(4).

FWIW, i386 & macppc platforms don't have this additional requirement. Copying from wd(4) to sd(4) works fine. Cylinder alignment is simply specific to Sun hardware done to improve performance.