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$ /usr/lib/apt/apt-helper download-file http://dl.bintray.com/i3/i3-autobuild-ubuntu/pool/main/i/i3-autobuild-keyring/i3-autobuild-keyring_2016.10.01_all.deb keyring.deb SHA256:460e8c7f67a6ae7c3996cc8a5915548fe2fee9637b1653353ec62b954978d844
# apt install ./keyring.deb
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$ /usr/lib/apt/apt-helper download-file http://dl.bintray.com/i3/i3-autobuild-ubuntu/pool/main/i/i3-autobuild-keyring/i3-autobuild-keyring_2016.10.01_all.deb keyring.deb SHA256:460e8c7f67a6ae7c3996cc8a5915548fe2fee9637b1653353ec62b954978d844
# apt install ./keyring.deb