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Open
/etc/apt/sources.list
and add the following line to the end.deb http://www.backports.org/debian jessie-backports main contrib non-free
or
deb http://ftp.us.debian.org/debian/ jessie-backports main contrib non-free deb-src http://ftp.us.debian.org/debian/ jessie-backports main contrib non-free
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Make sure the GPG …