apt-get update returns
W: Duplicate sources.list entry http://httpredir.debian.org/debian/ jessie-backports/main armhf Packages (/var/lib/apt/lists/httpredir.debian.org_debian_dists_jessie-backports_main_binary-armhf_Packages)
W: Duplicate sources.list entry http://httpredir.debian.org/debian/ jessie-backports/contrib armhf Packages (/var/lib/apt/lists/httpredir.debian.org_debian_dists_jessie-backports_contrib_binary-armhf_Packages)
W: Duplicate sources.list entry http://httpredir.debian.org/debian/ jessie-backports/non-free armhf Packages (/var/lib/apt/lists/httpredir.debian.org_debian_dists_jessie-backports_non-free_binary-armhf_Packages)
W: You may want to run apt-get update to correct these problems
cat /etc/apt/sources.list returns
deb http://httpredir.debian.org/debian jessie main contrib non-free
#deb-src http://httpredir.debian.org/debian jessie main contrib non-free
deb http://httpredir.debian.org/debian jessie-updates main contrib non-free
#deb-src http://httpredir.debian.org/debian jessie-updates main contrib non-free
deb http://httpredir.debian.org/debian jessie-backports main contrib non-free
#deb-src http://httpredir.debian.org/debian jessie-backports main contrib non-free
deb http://security.debian.org/ jessie/updates main contrib non-free
#deb-src http://security.debian.org/ jessie/updates main contrib non-free