sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-4.8 10 sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-4.9 20 sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-4.8 10 sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-4.9 20 sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-4.8 10 sudo update-alternatives --install /usr/
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