This tutorial assumes that you installed your Raspbian system to a SD-card and configured it to your taste. It also assumes that you have a partitioned usb device (e.g. a HDD, SDD or an usb-stick) with three partitions:
$ > fdisk -l /dev/sda
Disk /dev/sda: 7,5 GiB, 8011120640 bytes, 15646720 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
Disklabel type: dos
Disk identifier: 0x2052474d
Device Boot Start End Sectors Size Id Type
/dev/sda1 2048 165887 163840 80M c W95 FAT32 (LBA)
/dev/sda2 165888 8554495 8388608 4G 83 Linux
/dev/sda3 8554496 15646719 7092224 3,4G 83 Linux
The first (small) partition will be our future boot partition. The other partitions will serve as system-partitions for two installations. They should be at least 2-8GB large, depending on your needs. For Raspbian-Lite, 2-4GB will do fine, for a full desktop installation you should at least reserve 8GB. Anyhow, space should be no problem on modern HDDs/SDDs.
Note that you don't need to format the partitions, pi-boot-switch
can do this for you.
If you also want to boot from your usb-device, you should also prepare usb boot following this guide.
Personally I don't use usb boot, because it slows down the boot-process and it is not reliable enough (too many usb devices are not supported). I keep the boot-partition on the SD-card and the root-partition on usb.
The first step is to query partitition information using the option -I:
$ > sudo pi-boot-switch -I
Partition | Label | Role
----------------|------------------|---------------------
/dev/mmcblk0p1 | boot | current boot
/dev/mmcblk0p2 | | current root / next root
/dev/mmcblk0p3 | |
/dev/sda1 | |
/dev/sda2 | |
/dev/sda3 | |
Partitions on the SD-card are named like /dev/mmcblk0p1, partitions
on the usb-device have a /dev/sda prefix (if you use multiple
devices in parallel, you will also see /dev/sdb and so on).
Since we booted from the SD-card, the current boot-partition should be
/dev/mmcblk0p1 and the current root-partition is /dev/mmcblk0p2.
This will also be the next root-partition after a reboot.
To copy the root-partition, run
$ > sudo pi-boot-switch -c -t /dev/sda2 -F
info: formatting partition /dev/sda2 with ext4
info: mounting /dev/sda2 on /tmp/pi-boot-switch.FrSzev
info: copying / to /tmp/pi-boot-switch.FrSzev
info: fixing /etc/fstab on /dev/sda2
info: copying /boot/ to /tmp/pi-boot-switch.FrSzev/_boot
info: fixing /tmp/pi-boot-switch.FrSzev/_boot/cmdline.txt
info: copied system to /dev/sda2
info: use pi-boot-switch with option '-s /dev/sda2' to boot from new partition
info: setting label for /dev/sda2: raspbian 8
This will copy all files from the current root-partition to the new
root-partition (passed in with the target-option -t /dev/sda2). Since we
also used the option -F, the script will format /dev/sda2 with
the ext4-filesystem. If you already formatted your partition, just
omit this option.
You can also pass in the -v (verbose) option if you prefer
to have more output.
After the command has finished, run the info command again
$ > sudo pi-boot-switch -I
Partition | Label | Role
----------------|------------------|---------------------
/dev/mmcblk0p1 | boot | current boot
/dev/mmcblk0p2 | | current root / next root
/dev/mmcblk0p3 | |
/dev/sda1 | |
/dev/sda2 | raspbian 8 |
/dev/sda3 | |
As you can see, not much has changed. The partition /dev/sda2 now
has a label, but otherwise everything is as before.
There are two things to note: using -F destroys all existing data on
the target-partition, so be careful to select the correct partition.
Secondly, also without -F a copy operation is destructive. The
current root-partion is replicated to the target-partition and this
will overwrite all files and in addition automatically delete all
files on the target-partition which are not on the source-partition.
There is one exception if you also use the option -k: in this case,
the /home-directory is not copied to the target-partition. So you
keep data in the home-directories, but you would still loose all
configuration files e.g. in/etc. So make sure to backup all files
needed before you replicate.
The copy command will automatically label the selected partition, using
information found in /etc/os-release. Since we want a more meaningful
label, we change it with
$ > sudo pi-boot-switch -t sda2 -L "production"
info: setting label for /dev/sda2: production
$ > sudo pi-boot-switch -I
Partition | Label | Role
----------------|------------------|---------------------
/dev/mmcblk0p1 | boot | current boot
/dev/mmcblk0p2 | | current root / next root
/dev/mmcblk0p3 | |
/dev/sda1 | |
/dev/sda2 | production |
/dev/sda3 | |
Two things to note: the label is limited to 15 characters. Secondly, you
do not need to pass the /dev/ part for the partition name. This is
not limited to labelling, sda2 will always be a synonym for /dev/sda2.
We also label the root-partition on the SD-card. Since this is our
current root, we don't have to pass the -t xxx option:
$ > sudo pi-boot-switch -L "original"
info: setting label for /dev/mmcblk0p2: original
Until now, we only copied the system partition from the SD-card to the usb-device. The next command actually performs the switch:
$ > sudo pi-boot-switch -s -t sda2
info: copying /boot/ to /_boot
info: mounting /dev/sda2 on /tmp/pi-boot-switch.FOT7cc
info: copying /tmp/pi-boot-switch.FOT7cc/_boot/ to /boot
info: unmounting /dev/sda2
info: reboot the system to start from /dev/sda2
$ > sudo pi-boot-switch -I
Partition | Label | Role
----------------|------------------|---------------------
/dev/mmcblk0p1 | boot | current boot
/dev/mmcblk0p2 | original | current root
/dev/mmcblk0p3 | |
/dev/sda1 | |
/dev/sda2 | production | next root
/dev/sda3 | |
If you reboot the system now, it will boot from SD-card but the root-system
will be mounted on the partition /dev/sda2.
Note that switching the root-partition does not replicate user data. So don't be surprised that files you created (e.g. in /home/pi) are no longer there. They still exist, but on the original root-partition.
To replicate user-data you have to add the option -u. This will copy all
files from the /home-directory of the source-partition to the
/home-directory of the target partition.
If we also want to boot from the usb-device, we also need to copy the boot-partition from the SD-card to the usb-device:
$ > sudo pi-boot-switch -B -t sda1 -F
info: formatting partition /dev/sda1 with Fat32
mkfs.fat 3.0.27 (2014-11-12)
info: mounting /dev/sda1 on /tmp/pi-boot-switch.GZGPMR
info: copying /boot/ to /tmp/pi-boot-switch.GZGPMR
fatlabel: warning - lowercase labels might not work properly with DOS or Windows
info: fixing /boot in /etc/fstab on current root-partition
info: testing /dev/mmcblk0p1 ...
info: /dev/mmcblk0p1 is not a relevant partition
info: testing /dev/sda2 ...
info: found _boot, fixing /boot in /etc/fstab on partition /dev/sda2
info: testing /dev/sda1 ...
info: /dev/sda1 is not a relevant partition
info: activate USB-boot to and remove SD-card to boot from /dev/sda1
The option -F will again take care of formatting /dev/sda1. Note that
it is essential to first switch the system-partition and then copy
the boot-partition. Otherwise when booting from the usb-device the system will
still try to mount the old root-partition from the (non-existent) SD-card.
The command also updates the /etc/fstab of all systems to mount the
new boot-partition.
At this point you can shutdown the system, disconnect power, remove the SD-card and repower the system again. If you activated usb-boot as described in the prerequisites and your system (and device) is supported, then your system should boot normally. Running
$ > sudo pi-boot-switch -I
Partition | Label | Role
----------------|------------------|---------------------
/dev/mmcblk0p1 | boot |
/dev/mmcblk0p2 | original |
/dev/mmcblk0p3 | |
/dev/sda1 | boot | current boot
/dev/sda2 | production | current root / next root
/dev/sda3 | |
should confirm that you booted from /dev/sda1 and your current root is
/dev/sda2.
At this point we have an up and running Raspbian system labelled "production". One golden rule of IT is to never change a running system, at least not without a good backup. For this reason we copy the system to a new partition. This time we will use an all-in-one command to demonstrate that we can do all the steps we did above with separate commands with a single commandline:
$ > sudo pi-boot-switch -c -t sda3 -s -L "test" -F
info: formatting partition /dev/sda3 with ext4
info: mounting /dev/sda3 on /tmp/pi-boot-switch.NPKDvD
info: copying / to /tmp/pi-boot-switch.NPKDvD
info: fixing /etc/fstab on /dev/sda3
info: copying /boot/ to /tmp/pi-boot-switch.NPKDvD/_boot
info: fixing /tmp/pi-boot-switch.NPKDvD/_boot/cmdline.txt
info: copied system to /dev/sda3
info: reboot the system to start from /dev/sda3
info: copying /boot/ to /_boot
info: mounting /dev/sda3 on /tmp/pi-boot-switch.xDgauR
info: copying /tmp/pi-boot-switch.xDgauR/_boot/ to /boot
info: unmounting /dev/sda3
info: reboot the system to start from /dev/sda3
info: setting label for /dev/sda3: test
$ > sudo pi-boot-switch -I
Partition | Label | Role
----------------|------------------|---------------------
/dev/mmcblk0p1 | boot |
/dev/mmcblk0p2 | original |
/dev/mmcblk0p3 | |
/dev/sda1 | boot | current boot
/dev/sda2 | production | current root
/dev/sda3 | test | next root
We use the option -c to initiate copying of the current root-partition
to the target-partition (option -t sda3). We also switch to /dev/sda3
using option -s. Finally, we label the target-partition using the
option -L. Since we also want to format the target-partition, we use
the option -F. Note that the order of the options is not relevant.
So now we have two working installations, one on /dev/sda2 and one on
/dev/sda3. You can use pi-boot-switch -s to switch back and forth
between both versions. Don't forget to reboot in between, since
switching only changes the root-partition for the next-boot.
Let's assume you did some changes using the system on /dev/sda3
(labelled 'test'). Once you are satisfied you want to go productive. In this
case you can use the normal copy command (assuming you have booted the
system on sda3):
$ > sudo pi-boot-switch -c -t /dev/sda2
Without the format option -F this will copy new or differing files.
Note that this command will also delete all files on /dev/sda2 which
are not on /dev/sda3. So be very careful that you don't loose any files
you have created e.g. in your home-directory or in /etc!! If you add
the -k-option, user-data is not copied and the existing /home-directory
on the target-partition will not be touched.