Raspberry Pi and Roberto Piola

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pi.ilpiola.it: The site about Raspberry Pi and Roberto Piola

RPI Boot: dual boot with dual partitions on Raspberry Pi

Berryboot is a good attempt to have a multiple boot on the Raspberry Pi, but it has some drawbacks:

All OS must share the same kernel
Some OS updater may break the system (e.g. raspbmc)

So, I developed a system to place several OS instances on separated partitions of the SD card, and launch one from the other; it is not a multiboot in the strict sense, like grub, because the launcher can run only after the OS is up.

The idea behind it is that the nde SD will contain the two OS in two separate partitions, and that the shared boot partition will be overwritten, in turn, with the files coming from the boot partition for the first os or with the files from the boot partition of the second OS.

What you need

Unlike other systems, I developed rpiboot with the raspberry pi itself, and a secondary SD card reader connected on the usb port. Of course, the instructions can be easily adapted to a PC running Linux with a single card reader (you will need a PC anyway to ssh into the raspberry with raspbmc).

A Raspberry Pi with a running and configured raspbmc (or another complete OS) running on its SD (my first OS)
A second SD cartd with a running and configured raspbiano or anoher OS of choice (your second OS))
A second SD card reader connected to the USB port of the Pi
A new SD card large enough to hold both OS

let's go

First, insert the new SD card into the card reader connected to the PI, and open a terminal on the PI (ssh from a pc or an lxterminal window). If the SD is already foramtted, it will be mounted. Let's check and dismount it:

pi@raspbmc$ sudo su -
root@raspbmc:/boot# mount
/dev/mmcblk0p2 on / type ext4 (rw,noatime)
proc on /proc type proc (rw)
devpts on /dev/pts type devpts (rw,noexec,nosuid,relatime,gid=5,mode=620)
/dev/mmcblk0p1 on /boot type vfat (rw,noatime)
/dev/sdb1 on /media/035B-4020 type vfat (rw,nosuid,nodev,uid=1000,gid=1000,shortname=mixed,dmask=0077,utf8=1,showexec,uhelper=udisks)
/dev/sdb2 on /media/berryboot type ext4 (rw,nosuid,nodev,uhelper=udisks)
root@raspbmc:/boot# umount /dev/sdb1
root@raspbmc:/boot# umount /dev/sdb2/

Here, the mount command showed that the sd card reader has been detected as sdb, and that the two partitions of the sd card, namely sdb1 and sdb2, were automounted; I dismounted them with tue umount command.

Maybe your sd card reader will be detected as sda istead of sdb, or you will have just one, or more than two partitions to delete. Adapt the following instructions as follow. (You will not risk damaging your Pi... just your SD cards: if you make something wrong, you'll have to delete all partitions, reformat the cards and reinstall the OS).

So, go ahead and delete all partitions on /dev/sdb with the fdisk command:

 
root@raspbmc:/boot# fdisk /dev/sdb

Command (m for help): p

Disk /dev/sdb: 31.9 GB, 31914983424 bytes
64 heads, 32 sectors/track, 30436 cylinders, total 62333952 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1            2048      131071       64512    e  W95 FAT16 (LBA)
/dev/sdb2          131072    62333951    31101440   83  Linux

Command (m for help): d
Partition number (1-4): 2

Command (m for help): d
Selected partition 1

OK, now the sd card is completely free. We now will create several partitions:

partition#1 will be for the boot files, that will be overwritten when you switch OS
partition#2 will hold your primary OS (raspbmc, in this case)
partition#3 will hold your secondary OS (raspbian, in this case)
partition#4 is a container for extended partitions (for historical reasons, old OS were able to create only four partitions on a hard disk; more recent operating systems decided to standardize on creating subpartitions in the last standard partition, instead of revolutionizing the standard partition table to allow an arbitrary number of partitions)
partition#5 will hold the rpiboot files (boot images and scripts)
partition#6 will be a data partition shared between all OS (useful for your files)

You will be able to make any number of partitions for other OS, by shrinking partition#6 and creating partitions 7, 8, and so on

Partition#1 will be 200 M large, and will hold a FAT file system:

     

Command (m for help): n
Partition type:
   p   primary (0 primary, 0 extended, 4 free)
   e   extended
Select (default p): p
Partition number (1-4, default 1): 1
First sector (2048-62333951, default 2048):
Using default value 2048
Last sector, +sectors or +size{K,M,G} (2048-62333951, default 62333951): +200M

Command (m for help): t
Selected partition 1
Hex code (type L to list codes): e
Changed system type of partition 1 to e (W95 FAT16 (LBA))

Command (m for help): p

Disk /dev/sdb: 31.9 GB, 31914983424 bytes
64 heads, 32 sectors/track, 30436 cylinders, total 62333952 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1            2048      411647      204800    e  W95 FAT16 (LBA)

Partitions #2 and #3 will be 4 GB large, and will hold a linux filesystem (default type)

Command (m for help): n
Partition type:
   p   primary (1 primary, 0 extended, 3 free)
   e   extended
Select (default p): p
Partition number (1-4, default 2): 2
First sector (411648-62333951, default 411648):
Using default value 411648
Last sector, +sectors or +size{K,M,G} (411648-62333951, default 62333951): +4G

Command (m for help): n
Partition type:
   p   primary (2 primary, 0 extended, 2 free)
   e   extended
Select (default p): p
Partition number (1-4, default 3): 3
First sector (8800256-62333951, default 8800256):
Using default value 8800256
Last sector, +sectors or +size{K,M,G} (8800256-62333951, default 62333951): +4G

Then we'll make a four partition with all the remaining space, and we'll mark it as an "extended" partition for holding more logical partitions:

Command (m for help): n
Partition type:
   p   primary (3 primary, 0 extended, 1 free)
   e   extended
Select (default e): e
Selected partition 4
First sector (17188864-62333951, default 17188864):
Using default value 17188864
Last sector, +sectors or +size{K,M,G} (17188864-62333951, default 62333951):
Using default value 62333951

Now we'll make logical partitions #5 and #6:


Command (m for help): n
All primary partitions are in use
Adding logical partition 5
First sector (17190912-62333951, default 17190912):
Using default value 17190912
Last sector, +sectors or +size{K,M,G} (17190912-62333951, default 62333951): +200M

Command (m for help): n
All primary partitions are in use
Adding logical partition 6
First sector (17602560-62333951, default 17602560):
Using default value 17602560
Last sector, +sectors or +size{K,M,G} (17602560-62333951, default 62333951):
Using default value 62333951

Command (m for help): p

Disk /dev/sdb: 31.9 GB, 31914983424 bytes
64 heads, 32 sectors/track, 30436 cylinders, total 62333952 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1            2048      411647      204800    e  W95 FAT16 (LBA)
/dev/sdb2          411648     8800255     4194304   83  Linux
/dev/sdb3         8800256    17188863     4194304   83  Linux
/dev/sdb4        17188864    62333951    22572544    5  Extended
/dev/sdb5        17190912    17600511      204800   83  Linux
/dev/sdb6        17602560    62333951    22365696   83  Linux

at last, we'll quit fdisk and start formatting the partitions; before formatting, we'll check again if the automount process remounted some remainings of the first partition of the sdcard, and, if so, we umount them. Another thing worth noticing is that we'll add option -E nodiscard for formatting the linux filesystems: it greatly improves perforance on sdcards.

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.

WARNING: If you have created or modified any DOS 6.x
partitions, please see the fdisk manual page for additional
information.
Syncing disks.
root@raspbmc:/boot# mkfs.vfat /dev/sdb1
mkfs.vfat 3.0.13 (30 Jun 2012)
mkfs.vfat: /dev/sdb1 contains a mounted file system.
root@raspbmc:/boot# mount
/dev/mmcblk0p2 on / type ext4 (rw,noatime)
proc on /proc type proc (rw)
devpts on /dev/pts type devpts (rw,noexec,nosuid,relatime,gid=5,mode=620)
/dev/mmcblk0p1 on /boot type vfat (rw,noatime)
/dev/sdb1 on /media/035B-4020 type vfat (rw,nosuid,nodev,uid=1000,gid=1000,shortname=mixed,dmask=0077,utf8=1,showexec,uhelper=udisks)
root@raspbmc:/boot# umount /dev/sdb1
root@raspbmc:/boot# mkfs.vfat /dev/sdb1
mkfs.vfat 3.0.13 (30 Jun 2012)
root@raspbmc:/boot# 
root@raspbmc:/boot# mkfs.ext4 -E nodiscard -L /raspbmc /dev/sdb2
mke2fs 1.42.5 (29-Jul-2012)
Filesystem label=/raspbmc
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
262144 inodes, 1048576 blocks
52428 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=1073741824
32 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks:
        32768, 98304, 163840, 229376, 294912, 819200, 884736

Allocating group tables: done
Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done

root@raspbmc:/boot# mkfs.ext4 -E nodiscard -L /raspbian /dev/sdb3
mke2fs 1.42.5 (29-Jul-2012)
Filesystem label=/raspbian
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
262144 inodes, 1048576 blocks
52428 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=1073741824
32 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks:
        32768, 98304, 163840, 229376, 294912, 819200, 884736

Allocating group tables: done
Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done

root@raspbmc:/boot# mkfs.ext4 -E nodiscard -L /rpiutils /dev/sdb5
mke2fs 1.42.5 (29-Jul-2012)
Filesystem label=/rpiutils
OS type: Linux
Block size=1024 (log=0)
Fragment size=1024 (log=0)
Stride=0 blocks, Stripe width=0 blocks
51200 inodes, 204800 blocks
10240 blocks (5.00%) reserved for the super user
First data block=1
Maximum filesystem blocks=67371008
25 block groups
8192 blocks per group, 8192 fragments per group
2048 inodes per group
Superblock backups stored on blocks:
        8193, 24577, 40961, 57345, 73729

Allocating group tables: done
Writing inode tables: done
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done

root@raspbmc:/boot# mkfs.ext4 -E nodiscard -L /data /dev/sdb6
mke2fs 1.42.5 (29-Jul-2012)
Filesystem label=/data
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
1398096 inodes, 5591424 blocks
279571 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=0
171 block groups
32768 blocks per group, 32768 fragments per group
8176 inodes per group
Superblock backups stored on blocks:
        32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
        4096000

Allocating group tables: done
Writing inode tables: done
Creating journal (32768 blocks):  done
Writing superblocks and filesystem accounting information: done

root@raspbmc:/boot#

Done formatting, let's check the file systems:

root@raspbmc:/boot# mount
/dev/mmcblk0p2 on / type ext4 (rw,noatime)
proc on /proc type proc (rw)
devpts on /dev/pts type devpts (rw,noexec,nosuid,relatime,gid=5,mode=620)
/dev/mmcblk0p1 on /boot type vfat (rw,noatime)

Good: only raspbmc on the internal sd card is mounted. Let's mount the partitions that will hold raspbmc on the NEW card:

root@raspbmc:/boot# mount /dev/sdb2 /mnt/
root@raspbmc:/boot# mkdir /mnt/boot
root@raspbmc:/boot# mount /dev/sdb1 /mnt/boot/

And now, let's copy the raspbmc installation:

root@raspbmc:/boot# cd /
root@raspbmc:/# tar cf - --one-file-system / /boot | (cd /mnt ; tar xvfp -)
......

You will have enough time to brew and drink coffee or tea. When it finishes, we will update the fstab on the raspbmc partition on the new sdcard for forcing a mount of partition#5 on /rpiutils, (and also for forcing a mount of the other partitions under it, so that they will not show up under /media.... we will let the autmount process mount partition#6 under /media/_data like an external device) and we will make a copy of the boot partition; last, we will check fstab. Remember that, after inserting the sd card in the internal slot, the partitions will be renamed from /dev/sdXY to /dev/mmcblk0pY

root@raspbmc:/#cd /mnt
root@raspbmc:/mnt# mkdir rpiutils
root@raspbmc:/mnt# mount /dev/sdb5 rpiutils/
root@raspbmc:/mnt# mkdir /mnt/rpiutils/raspbmc
root@raspbmc:/mnt# mkdir /mnt/rpiutils/raspbian
root@raspbmc:/mnt# echo "/dev/mmcblk0p5 /rpiutils ext4 defaults,noatime 0 1" >> /mnt/etc/fstab ######################### CHECK
root@raspbmc:/mnt# echo "/dev/mmcblk0p2 /rpiutils/raspbmc ext4 defaults,noatime 0 1" >> /mnt/etc/fstab ######################### CHECK
root@raspbmc:/mnt# echo "/dev/mmcblk0p3 /rpiutils/raspbian ext4 defaults,noatime 0 1" >> /mnt/etc/fstab ######################### CHECK
root@raspbmc:/mnt# tar cvf rpiutils/boot-raspbmc.tar boot/
root@raspbmc:/mnt# cat /mnt/etc/fstab
################# paste

if everything is OK, shutdown the pi:

root@raspbmc:/mnt# shutdown -h now

Remove the raspbmc SD from the internal slot, and move the multiboot sd from the external reader to the internal slot, then reboot. Raspbmc will come up. Check that everything is OK, shutdown raspbmc, insert the raspbian-only SD in the internal slot, move the multiple boot SD into the esternal reader and reboot.

Raspbian should come up regularly, and automount the external SD under /media/something (boot partition), /media/_raspbian, /media/_raspbmc, /media/_rpiutils, /media/_data). First: let's dismount and remount the interesting partitions (all operations should be done as root):

pi@raspberrypi$ sudo su -
root@raspberrypi:/# umount /dev/sdb3
root@raspberrypi:/# mount /dev/sdb3 /mnt/
root@raspberrypi:/# mkdir /mnt/boot
root@raspberrypi:/# mount /dev/sdb1 /mnt/boot/

Then, copy the raspbian setup into the new directories:

root@rasperrypi:/# cd /
root@rasperrypi:/# tar cf - --one-file-system / /boot | (cd /mnt ; tar xvfp -)
......

Time for another coffee... now we will be ready to begin the tricky part: edit (with vi or your favorite editor), /mnt/boot/cmdline.cfg e /mnt/etc/fstab, replacing mmcblk0p2 (i.e.: the default root partition) with mmcblk0p3 (that is the NEW root partition)

root@rasperrypi:/# vi /mnt/boot/cmdline.cfg /mnt/etc/fstab
root@rasperrypi:/# cat /mnt/boot/cmdline.cfg
######### RIPORTARE 
root@rasperrypi:/# cat /mnt/etc/fstab
######### RIPORTARE

Now, like we did with raspbmc, we will make a copy of the boot files, and add rpiutils to the fstab:

root@raspberrypi:/mnt# mkdir data
root@raspberrypi:/mnt# mkdir rpiutils
root@raspberrypi:/mnt# mount /dev/sdb5 rpiutils
root@raspberrypi:/mnt# tar cvf rpiboot/boot-raspbian.tar boot/
root@raspberrypi:/mnt# echo "/dev/mmcblk0p5 /rpiutils ext4 defaults,noatime 0 1" >> /mnt/etc/fstab ######################### CHECK
root@raspberrypi:/mnt# echo "/dev/mmcblk0p2 /rpiutils/raspbmc ext4 defaults,noatime 0 1" >> /mnt/etc/fstab ######################### CHECK
root@raspberrypi:/mnt# echo "/dev/mmcblk0p3 /rpiutils/raspbian ext4 defaults,noatime 0 1" >> /mnt/etc/fstab ######################### CHECK

perform a clean shutdown, remove the raspbian-only SD and boot with the multiboot SD. Now the raspbian OS will be loaded. Open again a terminal and create the scripts to change identity:

pi@raspberrypi$ sudo su -
root@raspberrypi:/# cat <<*EOS* >/rpiutils/go-raspbian.sh
cd /
sudo /bin/rm /boot/*
sudo tar xf /rpiutils/boot-raspbian.tar
sudo shutdown -r now
*EOS*
root@raspberrypi:/# chmod a+x /rpiutils/go-raspbian.sh
root@raspberrypi:/# cat <<*EOS* >/rpiutils/go-raspbmc.sh
cd /
sudo /bin/rm /boot/*
sudo tar xf /rpiutils/boot-raspbmc.tar
sudo shutdown -r now
*EOS*
root@raspberrypi:/# chmod a+x /rpiutils/go-raspbmc.sh

/rpiutils/go-raspbmc.sh will be the magic command that will change your system from raspbian to raspbmc. Make a shortcut for it on your desktop (if you like), and then invoke it (it can be done as user pi)

pi@raspberrypi$ /rpiutils/go-raspbmc.sh

Your system will be restored to your raspbmc installation: install the "advanced launcher" addon and then add script /rpiutils/go-raspbian.sh as a linux program launcher, then use it to switch from raspbmc back to raspbian with your remote.

Notes

It is nice to have the same ip address (easy, if you use DHCP), same passwords and same ssh keys on both systems (I'm still working on how to have the same ssh keys, since raspbian and raspbmc use different ssh subsystems).
If you have additional codec licenses, be sure to configure them on the original SD cards BEFORE creating the multiboot card.
If some updater does updates your boot partition, remember to copy it back into the correct /rpiutils/boot-XXXXX.tar archive
If, for any reasons, your current OS becomes unable to boot, you may recover the system by restoring the contents of the boot partition (partition#1). It is a VFAT partition, so you'll be able to do it from a windows PC... just keep a copy of them off the sd card (or keep the original SD)

you can write me at roberto@ilpiola.it