Raspberry Pi: key-based authentication

  • Ubuntu 16.04 LTS
  • Raspberry Pi 3 Model B

Key-based authentication is a nice alternative to username/password-based login. Below is a basic process describing how to generate an RSA key pair and install public key on Raspberry Pi.

For more info see How to configure ssh key-based authentication on a linux server, or Securing your Raspberry Pi.

Create RSA key pair
$ ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/home/user/.ssh/id_rsa):        
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /home/user/.ssh/id_rsa.
Your public key has been saved in /home/user/.ssh/id_rsa.pub.
The key fingerprint is:

The key will be created in the ~/.ssh folder by default.

Upload public key to Raspberry Pi
$ cat ~/.ssh/id_rsa.pub | ssh pi@192.168.0.xxx "mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys"

Alternatively, use ssh-copy-id:

$ ssh-copy-id pi@192.168.0.xxx
DISABLE PASSWORD authentication (optional)

If higher level of security is required – consider disabling password authentication. Edit the following lines in /etc/ssh/sshd_config as shown below:

ChallengeResponseAuthentication no
PasswordAuthentication no
UsePAM no
Key-based authentication

Start ssh session as usually, password will not be required:

$ ssh pi@192.168.0.xxx

IoT-DSA: install and run broker-dart

  • Ubuntu 16.04 LTS
  • Dart VM version: 1.23.0 (Fri Apr 21 10:05:24 2017)
Install Dart

Taken from Installing Dart on Linux.

# Enable HTTPS for apt.
$ sudo apt-get update
$ sudo apt-get install apt-transport-https
# Get the Google Linux package signing key.
$ sudo sh -c 'curl https://dl-ssl.google.com/linux/linux_signing_key.pub | apt-key add -'
# Set up the location of the stable repository.
$ sudo sh -c 'curl https://storage.googleapis.com/download.dartlang.org/linux/debian/dart_stable.list > /etc/apt/sources.list.d/dart_stable.list'
$ sudo apt-get update
$ sudo apt-get install dart
Install and run broker-dart
$ sudo apth-get intsall https://github.com/IOT-DSA/broker-dart
$ cd broker-dart$ pub get
$ pub global run dsbroker:broker
[INFO][DSA] Listening on HTTP port 8080
[INFO][DSA] Listening on HTTP port 8443

Raspberry Pi: gdb debugging in Eclipse

If you want to do gdb debugging on command line – see Raspberry Pi: gdb debugging, command line.

In case you are interested how to debug Dart command line applications in IntelliJ – see Raspberry Pi: How to remote debug Dart command line applications in IntelliJ.

  • Ubuntu 16.04 LTS
  • Eclipse Neon.3 Release 4.6.3
  • arm-linux-gnueabihf (Ubuntu/Linaro 5.4.0-6ubuntu1~16.04.4) 5.4.0 20160609
  • Raspberry Pi 3 Model B

Based on this and this GuruCoding pages.

ARM toolchain

See Raspberry Pi: cross-compiling blog.

Install Eclipse IDE for C/C++ developers

Download and install from here.

Create and compile an example project

See Raspberry Pi: cross-compiling in Eclipse blog.

Set up remote access in Eclipse
  • Window > Perspective > Open perspective > Other > Remote System Explorer
  • File > New > Other > Remote System Explorer > Connection
  • Select Remote System Type:
    • Linux
    • Next
  • Remote System Connection:
    • Host name: raspberry-pi
    • Connection name: raspberry-pi
    • Next
  • Files:
    • Configuration: ssh.files
    • Next
  • Processes
    • Configuration: processes-shell-linux
    • Next
  • Shells:
    • Configuration: ssh-shells
    • Next
  • Ssh Terminals:
    • Configuration: ssh.terminals
    • Finish
  • Right click created connection > Properties
    • Host > Default User Id: pi
Create project

In Eclipse:

  • File > New > C++ Project
  • C++ Project
    • Project name: helloworld
    • Project type: Hello World C++ Project
    • Toolchains: Cross GCC
    • Next
  • Basic Settings
    • Hello world greeting: Hello world!
    • Next
  • Select Configurations
    • Next
  • Cross GCC Command
    • Cross compiler prefix: arm-linux-gnueabihf-
    • Cross compiler path: /usr/sbin
    • Finish
  • Right-click project name > Properties > C/C++ Settings
    • Tool Settings > Cross Settings
      • Prefix: arm-linux-gnueabihf-
      • Path: /usr/sbin
  • Project > Build All

Raspberry Pi: how to solve the “version `GLIBCXX_6.0.21′ not found” problem

  • Ubuntu 16.04 LTS
  • arm-linux-gnueabihf (Ubuntu/Linaro 5.4.0-6ubuntu1~16.04.4) 5.4.0 20160609
  • Raspberry Pi 3 Model B
Upgrade libstdc++ to 6.0.21

If you use arm-linux-gnueabihf toolchain (see Raspberry Pi: C++ cross-compiling) to build your applications for Raspberry Pi then there is a chance that you’ll have to upgrade your Raspbbery Pi libstdc++ to the toolchain’s version 6.0.21 (or later).


$ scp /usr/arm-linux-gnueabihf/lib/libstdc++.so.6.0.21 pi@192.168.0.xxx:/home/pi

Raspberry Pi:

$ sudo mv libstdc++.so.6.0.21 /usr/lib/arm-linux-gnueabihf/
$ sudo ln -s /usr/lib/arm-linux-gnueabihf/libstdc++.so.6.0.21 /usr/lib/arm-linux-gnueabihf/libstdc++.so.6

Raspberry Pi: install Dart VM, create and run helloword.dart

  • Ubuntu 16.04 LTS
  • arm-linux-gnueabihf (Ubuntu/Linaro 5.4.0-6ubuntu1~16.04.4) 5.4.0 20160609
  • Dart SDK, master 1.24.0-edge.eb1839b8fd453b6c0c93376346743fa96db48440
  • Raspberry Pi 3 Model B
Download and build Dart SDK

See Dart: build Dart SDK for x86 and ARM.

Important: though Raspberry Pi 3 has a 64-bit CPU the Raspbian OS does not support 64-bit builds at the moment of writing – we will build 32-bit Dart SDK for ARM.

Alternatively, you can download pre-built Dart SDK for ARM:

$ wget https://storage.googleapis.com/dart-archive/channels/stable/release/2.2.0/sdk/dartsdk-linux-arm-release.zip.sha256sum
Upgrade libstdc++ to 6.0.21

See Raspberry Pi: how to solve the “version `GLIBCXX_6.0.21′ not found” problem.

Copy Dart VM to Raspbbery Pi


$ cd dart-sdk/sdk
$ scp -r out/ReleaseXARM/dart-sdk/bin/dart pi@192.168.0.xxx:/home/pi

Raspberry Pi:

$ sudo mv dart /usr/local/bin

Restart Raspberry Pi ssh session, then check if Dart VM works:

$ dart --version
Dart VM version: 1.24.0-edge.eb1839b8fd453b6c0c93376346743fa96db48440 (Sun Apr 16 18:04:59 2017) on "linux_arm"
Hello World application

Create helloworld.dart file with the following content:

main() {
  print('Hello world!');

Run the application:

$ dart helloworld.dart 
Hello world!

Dart: build Dart SDK for x86 and ARM

Based on Building Dart, Building Dart SDK for ARM processors and Building Dart SDK for Raspberry Pi.

  • Ubuntu 16.04 LTS
  • arm-linux-gnueabihf (Ubuntu/Linaro 5.4.0-6ubuntu1~16.04.4) 5.4.0 20160609
  • Dart SDK, master f6a2fb0050eeaf24706da66bdd73c2f3c9770f96
x86 toolchain

Pre-installed in Ubuntu (16.04 LTS).

ARM 32-bit toolchain

See Raspberry Pi: C++ cross-compiling .

ARM 64-bit toolchain
$ sudo apt-get install g++-aarch64-linux-gnu
Other build tools
$ sudo apt-get install g++ git make python
$ sudo apt-get install g++-multilib
Install Chromium depot_toops
$ git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git
$ export PATH="$PATH:$PWD/depot_tools"
Get the source
$ mkdir dart-sdk
$ cd dart-sdk
$ gclient config https://github.com/dart-lang/sdk.git
### Checkout HEAD
$ gclient sync
### Checkout a tag, e.g. 1.9.3
$ gclient sync --revision=1.9.3
Create (if missing) symbolic links

create_sdk build will fail if the following symbolic links are missing:

$ sudo ln -s /usr/include/x86_64-linux-gnu/asm/ /usr/include/asm
$ sudo ln -s /usr/include/x86_64-linux-gnu/bits/ /usr/include/bits
Build 64-bit x86
$ cd dart-sdk/sdk
$ ./tools/build.py --mode release --arch x64 create_sdk
Build 32-bit x86
$ cd dart-sdk/sdk
$ ./tools/build.py --mode release --arch ia32 create_sdk
Build for 32-bit ARM
$ cd dart-sdk/sdk
$ ./tools/build.py --mode release --arch arm create_sdk

The build fails (master #eb1839b):

g++ -MMD -MF x86/obj/runtime/bin/gen_snapshot_dart_io/eventhandler_linux.o.d -DDART_IO_SECURE_SOCKET_DISABLED -D_FORTIFY_SOURCE=2 -DNDEBUG -DTARGET_OS_LINUX -DTARGET_ARCH_ARM -DNDEBUG -DDART_USE_TCMALLOC -DDART_PRECOMPILER -I../../runtime -I../../third_party -I../.. -Ix86/gen -I../../third_party/tcmalloc/gperftools/src -I../../third_party/zlib -m32 -msse2 -mfpmath=sse -fno-exceptions -pthread -Wall -Wextra -Werror -Wendif-labels -Wno-missing-field-initializers -Wno-unused-parameter -Wno-unused-local-typedefs -O3 -fno-ident -fdata-sections -ffunction-sections -g3 -ggdb3 -Werror -Wall -Wextra -Wno-unused-parameter -Wnon-virtual-dtor -Wvla -Wno-conversion-null -Woverloaded-virtual -g3 -ggdb3 -fno-rtti -fno-exceptions -O3 -fvisibility-inlines-hidden -fno-omit-frame-pointer -fno-rtti -fno-exceptions -c ../../runtime/bin/eventhandler_linux.cc -o x86/obj/runtime/bin/gen_snapshot_dart_io/eventhandler_linux.o
In file included from ../../runtime/vm/simulator_arm.h:19:0,
                 from ../../runtime/vm/simulator.h:15,
                 from ../../runtime/vm/atomic.h:11,
                 from ../../runtime/bin/reference_counting.h:8,
                 from ../../runtime/bin/socket.h:14,
                 from ../../runtime/bin/eventhandler_linux.cc:27:
../../runtime/vm/constants_arm.h:263:17: error: ‘dart::STMP’ defined but not used [-Werror=unused-variable]
 const SRegister STMP = EvenSRegisterOf(DTMP);
cc1plus: all warnings being treated as errors
ninja: build stopped: subcommand failed.

This can be fixed by changing the dart-sdk/sdk/runtime/vm/constants_arm.h file, lines 262-263 from:

const DRegister DTMP = EvenDRegisterOf(QTMP);  
const SRegister STMP = EvenSRegisterOf(DTMP);


const DRegister DTMP __attribute__((unused)) = EvenDRegisterOf(QTMP);  
const SRegister STMP __attribute__((unused)) = EvenSRegisterOf(DTMP);

Raspberry Pi note: This procedure will produce a useful Dart VM – the dart and pub utilities.

Pre-built 32-bit ARM Dart SDK image
$ wget http://share.geomodule.com/dart-sdk-f6a2fb0050eeaf24706da66bdd73c2f3c9770f96.tar.gz
Build for 64-bit ARM
$ cd dart-sdk/sdk
./tools/build.py --mode release --arch arm64 create_sd
Install Dart SDK on Raspberry Pi

Make sure you have correct version of the GLIBCXX library, see here:


# On your build host host
$ cd dart-sdk
$ scp -r sdk/out/ReleaseXARM/dart-sdk pi@192.168.0.xxx:~/dart-sdk
# On Raspberry Pi
# Add the following line at the end of .bashrc
# export PATH=${PATH}:/home/pi/dart-sdk/bin
$ dart --version
Dart VM version: 1.24.0-edge.eb1839b8fd453b6c0c93376346743fa96db48440 (Sun Apr 16 18:04:59 2017) on "linux_arm"
$ pub --version
Pub 1.25.0-edge.511963d71509de50ac577ac22f3bac8d33c17e34

Git: links, cheatsheets, tutorials, etc…

setup git credentials store
$ git config credential.helper store
$ git config credential.helper store --file=github
merge and rebase

Atlassian Merge vs Rebase tutorial.

Rename local and remote branch

Taken from here.

### Rename local branch
$ git branch -m new-name
### Rename local branch if you are on a different branch
$ git branch -m old-name new-name
# Remove old remote and push new local branch
$ git push origin :old-name new-name
### Reset upstream branch for thew name, switch to the new local
$ git push origin -u new-name
### Remote
$ git push --delete <remote_name> <branch_name>
### Or
$ git branch -rd <branch_name>
### Local
$ git branch -d <branch_name>
### Squash merge
$ git checkout develop
$ git merge --squash feature/branch
### Revert to a specific commit
$ git checkout -f COMMITID -- .
$ git commit -a

### Revert a specific commit
$ git revert --no-commit COMMITID
git flow

Nice git flow cheatsheet.

git stash

Good tutorial from Atlassian.

git submodules

Good tutorial from Jon Cairns.

Export existing git project to Github/Bitbucket

More details see on How can I export the project in Eclipse to a GitHub repository:

# github
$ git remote add origin git@github.com:<username>/<reponame>.git
# bitbucket
$ git remote add origin https://<username>@bitbucket.org/<username>/<reponame>.git
$ git push -u origin master
Find branch point

Taken from stackoverflow:

$ git log --pretty=oneline master > 1
$ git log --pretty=oneline branch_A > 2
$ git rev-parse `diff 1 2 | tail -1 | cut -c 3-42`^

CMake: cross-compile GoogleTest

This post is about how to cross-compile GoogleTest in Eclipse.

  • Ubuntu 16.04 LTS
  • Eclipse Neon.3 Release 4.6.3
Install CMake
$ sudo apt-get install cmake
Checkout GoogleTest
$ git clone https://github.com/google/googletest.git
Configure ARM toolchain

How to install ARM toolchain see Raspberry Pi: C++ cross-compiling.

  • Create in the root of GoogleTest folder  toolchain-arm-linux-gnueabihf.cmake file with the following content:
# Target system

set(CMAKE_FIND_ROOT_PATH /usr/arm-linux-gnueabihf)

# Cross compiler
SET(CMAKE_C_COMPILER   /usr/bin/arm-linux-gnueabihf-gcc)
SET(CMAKE_CXX_COMPILER /usr/bin/arm-linux-gnueabihf-g++)

# Search for programs in the build host directories

# Libraries and headers in the target directories
  • Configure CMake:
$ cmake -DCMAKE_TOOLCHAIN_FILE=./toolchain-arm-linux-gnueabihf.cmake
Create Eclipse project
$ cmake -G "Eclipse CDT4 - Unix Makefiles"

Import the project in Eclipse:

  • File > Import
  • Select:
    • General
    • Existing Project into Workspace
    • Next
  • Select project
    • Select root directory > Browse (to the GoogleTest folder)
    • Finish
Compile GoogleTest


Project > Build project

Check library type
$ readelf -a -W ./googlemock/gtest/libgtest.a | more

File: ./googlemock/gtest/libgtest.a(gtest-all.cc.o)
ELF Header:
  Magic:   7f 45 4c 46 01 01 01 03 00 00 00 00 00 00 00 00 
  Class:                             ELF32
  Data:                              2's complement, little endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - GNU
  ABI Version:                       0
  Type:                              REL (Relocatable file)
  Machine:                           ARM
  Version:                           0x1
  Entry point address:               0x0
  Start of program headers:          0 (bytes into file)
  Start of section headers:          1328016 (bytes into file)
  Flags:                             0x5000000, Version5 EABI
  Size of this header:               52 (bytes)
  Size of program headers:           0 (bytes)
  Number of program headers:         0
  Size of section headers:           40 (bytes)
  Number of section headers:         10368
  Section header string table index: 10365