OS images for USB disks: Difference between revisions
(reworked using images an on existing partition) |
m (fixed formatting error) |
||
Line 36: | Line 36: | ||
==== ''OLPCRoot'' volume label ==== |
==== ''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: |
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/sdb1 |
# tune2fs -L OLPCRoot /dev/sdb1 |
Revision as of 19:02, 23 August 2006
Dedicated USB disk
If you can devote an entire USB flash drive or hard disk for trying images out, using the images is easy.
To try out an image, simply download the appropriate .img.bz2 file, e.g.,
olpc-stream-development-42-20060714_1709-rpm-ext3.img.bz2
unzip it, and transfer it to a USB storage device via dd, e.g.,
# bunzip2 olpc-stream-development-42-20060714_1709-rpm-ext3.img.bz2 # dd if=olpc-stream-development-42-20060714_1709-rpm-ext3.img of=/dev/sdb bs=1M # sync
Remember to:
- Make sure any old partitions from the storage device are unmounted.
- Do this as the super user / root
- Replace /dev/sdb with the device file of the USB storage device. The images do contain a partition table and boot loader, so make sure to write to the device and not a partition on the device (e.g. not /dev/sdb1)
- The USB storage device must be 512 MB or larger. All existing data will be lost.
Now you should be able to boot the OLPC operating system off the USB storage device.
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.
Partitioning
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/sdb1
Where /dev/sdb1 is the partition containing your root FS.
Mounting the image
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/usbdisk
Bootloader setup
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.