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Building TensorFlow for Raspberry Pi: a Step-By-Step Guide

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What You Need

  • Raspberry Pi 2 or 3 Model B
  • An SD card running Raspbian with several GB of free space
    • An 8 GB card with a fresh install of Raspbian does not have enough space. A 16 GB SD card minimum is recommended.
    • These instructions may work on Linux distributions other than Raspbian
  • Internet connection to the Raspberry Pi
  • A USB memory drive that can be installed as swap memory (if it is a flash drive, make sure you don't care about the drive). Anything over 1 GB should be fine
  • A fair amount of time

Overview

These instructions were crafted for a Raspberry Pi 3 Model B running a vanilla copy of Raspbian 8.0 (jessie). It appears to work on Raspberry Pi 2, but there are some kinks that are being worked out. If these instructions work for different distributions, let me know!

Here's the basic plan: build a 32-bit version of Protobuf, use that to build a RPi-friendly version of Bazel, and finally use Bazel to build TensorFlow.

Contents

  1. Install basic dependencies
  2. Build Protobuf
  3. Build Bazel
  4. Install USB Memory as Swap
  5. Compiling TensorFlow
  6. Cleaning Up
  7. References

The Build

1. Install basic dependencies

First, update apt-get to make sure it knows where to download everything.

sudo apt-get update

Next, install some base dependencies and tools we'll need later.

For Protobuf:

sudo apt-get install autoconf automake libtool maven

For Bazel:

sudo apt-get install pkg-config zip g++ zlib1g-dev unzip

For TensorFlow:

# For Python 2.7
sudo apt-get install python-pip python-numpy swig python-dev
sudo pip install wheel

# For Python 3.3+
sudo apt-get install python3-pip python3-numpy swig python3-dev
sudo pip3 install wheel

Finally, for cleanliness, make a directory that will hold the Protobuf, Bazel, and TensorFlow repositories.

mkdir tf
cd tf

2. Build Protobuf

Clone the Protobuf repository.

git clone https://github.com/google/protobuf.git

Now move into the new protobuf directory, configure it, and make it. Note: this takes a little while.

cd protobuf
git checkout d5fb408d
./autogen.sh
./configure --prefix=/usr
make -j 4
sudo make install

Once it's made, we can move into the java directory and use Maven to build the project.

cd java
mvn package

After following these steps, you'll have two spiffy new files: /usr/bin/protoc and protobuf/java/core/target/protobuf-java-3.0.0-beta2.jar

3. Build Bazel

First, move out of the protobuf/java directory and clone Bazel's repository.

cd ../..
git clone https://github.com/bazelbuild/bazel.git

Next, go into the new bazel direcotry and immediately checkout version 0.2.1 of Bazel.

cd bazel
git checkout 0.2.1

After that, copy the two Protobuf files mentioned earlier into the Bazel project. Note the naming of the files in this step- it must be precise.

sudo cp /usr/bin/protoc third_party/protobuf/protoc-linux-arm32.exe
sudo cp ../protobuf/java/target/protobuf-java-3.0.0-beta-2.jar third_party/protobuf/protobuf-java-3.0.0-beta-1.jar

Before building Bazel, we need to set the javac maximum heap size for this job, or else we'll get an OutOfMemoryError. To do this, we need to make a small addition to bazel/scripts/bootstrap/compile.sh. (Shout-out to @SangManLINUX for pointing this out..

nano scripts/bootstrap/compile.sh

Move down to line 128, where you'll see the following block of code:

run "${JAVAC}" -classpath "${classpath}" -sourcepath "${sourcepath}" \
      -d "${output}/classes" -source "$JAVA_VERSION" -target "$JAVA_VERSION" \
      -encoding UTF-8 "@${paramfile}"

At the end of this block, add in the -J-Xmx500M flag, which sets the maximum size of the Java heap to 500 MB:

run "${JAVAC}" -classpath "${classpath}" -sourcepath "${sourcepath}" \
      -d "${output}/classes" -source "$JAVA_VERSION" -target "$JAVA_VERSION" \
      -encoding UTF-8 "@${paramfile}" -J-Xmx500M

Now we can build Bazel! Note: this also takes some time.

./compile.sh

When the build finishes, you end up with a new binary, output/bazel. Copy that to your /usr/local/bin directory.

sudo mkdir /usr/local/bin
sudo cp output/bazel /usr/local/bin/bazel

To make sure it's working properly, run bazel on the command line and verify it prints help text. Note: this may take 15-30 seconds to run, so be patient!

$ bazel

Usage: bazel <command> <options> ...

Available commands:
  analyze-profile     Analyzes build profile data.
  build               Builds the specified targets.
  canonicalize-flags  Canonicalizes a list of bazel options.
  clean               Removes output files and optionally stops the server.
  dump                Dumps the internal state of the bazel server process.
  fetch               Fetches external repositories that are prerequisites to the targets.
  help                Prints help for commands, or the index.
  info                Displays runtime info about the bazel server.
  mobile-install      Installs targets to mobile devices.
  query               Executes a dependency graph query.
  run                 Runs the specified target.
  shutdown            Stops the bazel server.
  test                Builds and runs the specified test targets.
  version             Prints version information for bazel.

Getting more help:
  bazel help <command>
                   Prints help and options for <command>.
  bazel help startup_options
                   Options for the JVM hosting bazel.
  bazel help target-syntax
                   Explains the syntax for specifying targets.
  bazel help info-keys
                   Displays a list of keys used by the info command.

Move out of the bazel directory, and we'll move onto the next step.

cd ..

4. Install a Memory Drive as Swap for Compiling

In order to succesfully build TensorFlow, your Raspberry Pi needs a little bit more memory to fall back on. Fortunately, this process is pretty straightforward. Grab a USB storage drive that has at least 1GB of memory. I used a flash drive I could live without that carried no important data. That said, we're only going to be using the drive as swap while we compile, so this process shouldn't do too much damage to a relatively new USB drive.

First, put insert your USB drive, and find the /dev/XXX path for the device.

sudo blkid

As an example, my drive's path was /dev/sda1

Once you've found your device, unmount it by using the umount command.

sudo umount /dev/XXX

Then format your device to be swap:

sudo mkswap /dev/XXX

If the previous command outputted an alphanumeric UUID, copy that now. Otherwise, find the UUID by running blkid again. Copy the UUID associated with /dev/XXX

sudo blkid

Now edit your /etc/fstab file to register your swap file. (I'm a Vim guy, but Nano is installed by default)

sudo nano /etc/fstab

On a separate line, enter the following information. Replace the X's with the UUID (without quotes)

UUID=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX none swap sw,pri=5 0 0

Save /etc/fstab, exit your text editor, and run the following command:

sudo swapon -a

If you get an error claiming it can't find your UUID, go back and edit /etc/fstab. Replace the UUID=XXX.. bit with the original /dev/XXX information.

sudo nano /etc/fstab
# Replace the UUID with /dev/XXX
/dev/XXX none swap sw,pri=5 0 0

Alright! You've got swap! Don't throw out the /dev/XXX information yet- you'll need it to remove the device safely later on.

5. Compiling TensorFlow

First things first, clone the TensorFlow repository and move into the newly created directory.

git clone --recurse-submodules https://github.com/tensorflow/tensorflow
cd tensorflow

Note: if you're looking to build to a specific version or commit of TensorFlow (as opposed to the HEAD at master), you should git checkout it now.

Once in the directory, we have to write a nifty one-liner that is incredibly important. The next line goes through all files and changes references of 64-bit program implementations (which we don't have access to) to 32-bit implementations. Neat!

grep -Rl 'lib64'| xargs sed -i 's/lib64/lib/g'

Next, we need to delete a particular line in tensorflow/core/platform/platform.h. Open up the file in your favorite text editor:

$ sudo nano tensorflow/core/platform/platform.h

Now, scroll down toward the bottom and delete the following line containing #define IS_MOBILE_PLATFORM:

#elif defined(__arm__)
#define PLATFORM_POSIX
...
#define IS_MOBILE_PLATFORM   <----- DELETE THIS LINE

This keeps our Raspberry Pi device (which has an ARM CPU) from being recognized as a mobile device.

Now let's configure Bazel:

$ ./configure

Please specify the location of python. [Default is /usr/bin/python]: /usr/bin/python
Do you wish to build TensorFlow with Google Cloud Platform support? [y/N] N
Do you wish to build TensorFlow with GPU support? [y/N] N

Note: if you want to build for Python 3, specify /usr/bin/python3 for Python's location.

Now we can use it to build TensorFlow! Warning: This takes a really, really long time. Several hours.

bazel build -c opt --copt="-mfpu=neon" --local_resources 1024,1.0,1.0 --verbose_failures tensorflow/tools/pip_package:build_pip_package

Note: I toyed around with telling Bazel to use all four cores in the Raspberry Pi, but that seemed to make compiling more prone to completely locking up. This process takes a long time regardless, so I'm sticking with the more reliable options here. If you want to be bold, try using --local_resources 1024,2.0,1.0 or --local_resources 1024,4.0,1.0

When you wake up the next morning and it's finished compiling, you're in the home stretch! Use the built binary file to create a Python wheel.

bazel-bin/tensorflow/tools/pip_package/build_pip_package /tmp/tensorflow_pkg

And then install it!

sudo pip install /tmp/tensorflow_pkg/tensorflow-0.9-cp27-none-linux_armv7l.whl

6. Cleaning Up

There's one last bit of house-cleaning we need to do before we're done: remove the USB drive that we've been using as swap.

First, turn off your drive as swap:

sudo swapoff /dev/XXX

Finally, remove the line you wrote in /etc/fstab referencing the device

sudo nano /etc/fstab

Then reboot your Raspberry Pi.

And you're done! You deserve a break.

References

  1. Building TensorFlow for Jetson TK1
  2. Turning a USB Drive into swap
  3. Safely removing USB swap space

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