Ubuntu18.04 selenium geckodriver chromedriver "Tried to run command without establishing a connection"

Tried to run command without establishing a connection (Selenium::WebDriver::Error::InvalidSessionIdError)

2G未満のRAMだと、Window数個でドライバーがクラッシュ、結果このエラーがでる。

geckodriverのダウンロード
　https://github.com/mozilla/geckodriver/releases

geckodriverの設置場所

/usr/bin/geckodriver

## Geckodriver
wget https://github.com/mozilla/geckodriver/releases/download/v0.23.0/geckodriver-v0.23.0-linux64.tar.gz
sudo sh -c 'tar -x geckodriver -zf geckodriver-v0.23.0-linux64.tar.gz -O > /usr/bin/geckodriver'
sudo chmod +x /usr/bin/geckodriver
rm geckodriver-v0.23.0-linux64.tar.gz

## Chromedriver
wget https://chromedriver.storage.googleapis.com/2.29/chromedriver_linux64.zip
unzip chromedriver_linux64.zip
sudo chmod +x chromedriver
sudo mv chromedriver /usr/bin/
rm chromedriver_linux64.zip