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

Make sure the GPG …

According to https://www.sqlite.org/lockingv3.html, POSIX advisory locking is known to be buggy or even unimplemented on many NFS implementations (including recent versions of Mac OS X) and that there are reports of locking problems for network filesystems under Windows. So, the rule of thumb is to …