I assume that you use rbenv.

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Update your rbenv and ruby-build

cd ~/.rbenv && git pull

cd "$(rbenv root)"/plugins/ruby-build && git pull

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Check what versions are installed

rbenv versions

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Check what versions of Ruby are available for installing

rbenv install -l

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Install Ruby in some version

rbenv install 2.4.2

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Create the project directory and go there

mkdir ~/projects/hosting_manager

cd ~/projects/hosting_manager/

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Switch the directory to your Ruby version

rbenv local 2.4.2

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Install Bundler and init it

gem install bundler

bundle init

bundle install --path vendor/bundle