OS images for USB disks
(see talk or discussion page)
Notes before beginning...
- This page presumes that you'll be using the disks you create on OLPC's "XO" hardware. While you could try to boot a normal PC with them (making sure you select the OLPC Simulator option), there are other ways to run the OLPC's Sugar user interface on a PC, see Emulating the XO.
- By default, the images boot with the GRUB boot option OLPC USB. This is what you want if you're booting from a USB disk connected to OLPC hardware.
The OS images that OLPC creates for each release contain the computer instructions of the OLPC software. If you present those to an XO, it will run them. But the XO has to boot, read these machine instructions from the file system on the USB, and then use that file system. The OLPC operating system's layout is incompatible with the "FAT" filesystem set up on most USB drives, it requires permissions and symbolic links that FAT does not provide. ("Live" CDs and USBs for Linux get around this limitation by packing a UNIX file system into simple files on the CD or USB drive which the computer unpacks during boot.)
So you must
- create a file system on the USB drive with the necessary characteristics
- put the OLPC release's files in this file system
- modify the boot instructions in the file system
before you can attempt to boot an XO from the USB drive
USB disk with existing partitions
If you don't want to completely wipe the USB stick or hard drive, you can also try transferring the partition within the image file into an existing partition on your storage device. Using dd to transfer the image directly onto the device completely replaces the existing data and partition table. Instead, you can use loopback mounts to copy the partition across and then set-up grub on the device.
Don't follow this set of instructions if you don't know how to partition your disk or create filesystems. There are some things you need to know that the OS images assume:
ext3 root filesystem
Make sure the root partition is the ext3 filesystem, not ext2.
OLPCRoot volume label
The OS images look for the volume label OLPCRoot to determine the root FS. You can set this for an ext3 filesystem with:
# tune2fs -L OLPCRoot /dev/sdX1
Where /dev/sdX1 is the partition containing your root FS.
Extracting a build's files
Since 2010 or so the OLPC Build system does not retain a generic Linux filesystem image, it produces images specific to the built-in flash memory of different XO models. However, many builds contain the filesystem contents in a file named osNN.tree.tar.lzma
After downloading the .tree.tar.lzma file appropriate for your XO, you need to extract these files to the partition on your device, preserving their attributes and ownership. One way to extract these files to your partition.
- Insert the SD card or USB drive and allow your operating system to mount it.
- Change to its root directory, e.g.
% cd /media/OLPCRoot
- (Note that /media changes to /run/media/olpc for Fedora 17 based builds used in 12.1.0 and later).
- "Untar" the files, e.g.
% sudo tar --lzma --numeric-owner -xvf /path/to/downloaded/osNN.tree.tar.lzma
- You need to create a symbolic link from the boot directory to /boot, e.g.
% sudo ln -s versions/pristine/NN/boot boot'
- ?? You need to make additional changes to the boot path in olpc.fth and initrd ?? See ticket #11233.
- Safely remove the SD card or USB drive
- % sync
Now you try booting. Insert the USB drive, power on the XO holding down the check game key to see details, and then press [Esc] to disable the normal boot process. Then enter something like (see Custom bootloader):
ok boot U:\boot\vmlinuz
Mounting an image to extract files
JFFS2 XO-1 images
In theory you can mount a JFFS2 .img of the XO-1 file system under Linux and get the files from that. The JFFS2 FAQ mentions some issues.
Old ext3 images
Retrieve and unzip the appropriate OLPC image file as described above. This file contains a partition table, which describes exactly one partition. What we want to do is to mount that partition (using a loopback device) and copy the contents to the USB hard disk, then make that hard disk bootable.
First, we need to setup the image file on a loopback device so we can inspect that partition table:
# losetup /dev/loop0 olpc-stream-development-59-20060808_1153-rpm-ext3.img
Now, use fdisk to look at the contents:
# fdisk -l -u /dev/loop0
Disk /dev/loop0: 504 MB, 504626688 bytes 16 heads, 32 sectors/track, 1924 cylinders, total 985599 sectors Units = sectors of 1 * 512 = 512 bytes Device Boot Start End Blocks Id System /dev/loop0p1 32 985599 492784 83 Linux
In this case, the partition we want starts at sector 32, and each sector is 512 bytes = 16384 bytes into the image file. Now, we can set up a second loopback device to load this partition and mount it:
# losetup /dev/loop1 -o 16384 olpc-stream-development-59-20060808_1153-rpm-ext3.img # mount -text3 /dev/loop1 /media/tmp/
Copying files to the new disk
Now, copy the files to your USB hard disk:
# cd /media/tmp # find | cpio -p --unconditional --preserve-modification-time --dot /media/OLPCRoot
Since LinuxBIOS is no longer on olpc , GRUB is useless. Just reboot your olpc and it will start on USB key . To verify type "df" or "mount" in a terminal
And finally, we need to set up grub on the disk to boot from the first partition. We do this using the GRUB shell. Note that in this example, we're installing on (hd1), because the external disk is the 2nd disk connected to the system. When it boots on the OLPC board, it will be the primary disk and grub will treat it as (hd0)
# grub Probing devices to guess BIOS drives. This may take a long time. # grub> root (hd1) root (hd1) Filesystem type unknown, using whole disk # grub> root (hd1,0) root (hd1,0) Filesystem type is ext2fs, partition type 0x83 grub> setup (hd1) setup (hd1) Checking if "/boot/grub/stage1" exists... yes Checking if "/boot/grub/stage2" exists... yes Checking if "/boot/grub/e2fs_stage1_5" exists... yes Running "embed /boot/grub/e2fs_stage1_5 (hd1)"... 15 sectors are embedded. succeeded Running "install /boot/grub/stage1 (hd1) (hd1)1+15 p (hd1,0)/boot/grub/stage2 /boot/grub/menu.lst"... succeeded Done. # grub> ^C #
- When I tried booting from this drive on the OLPC, GRUB started but didn't load its configuration correctly - just dropping me into the grub shell instead. I needed to run 'root' and 'setup' again on the actual board to get GRUB to set itself up right. If anyone knows how to avoid this step, please fix the instructions.
To solve the Problem you have to insert two lines in each sector of /media/OLPCRoot/boot/grub/menu.lst (possibly grub.conf, whatever is printed out above):
map (hd0) (hd1) map (hd1) (hd0)
Dedicated USB disk
The #Dedicated USB disk method described here combines step 1 (create a file system on the USB drive with the necessary characteristics) and 2 (put the OLPC release's files in this file system) by dumping an XO image complete with a partition table and ext3 filesystem onto the USB drive.
However, as of 2010 OLPC's Build system no longer creates such images. The XO-1 osNNN.img file is the raw JFFS2 contents and does not work copied to a USB flash drive.
- **A tar-based copy would use the existing file system and partitions. New instructions needed.** --FGrose 15:18, 4 February 2009 (UTC)
- Consider the cpio-based method described in #USB disk with existing partitions.
USB Boot images