You are about to install software that can't be authenticated
by ychaouche from LinuxQuestions.org on (#5BM63)
https://i.imgur.com/YdRCMUK.png
This has been a first since I am using mint (2015). I didn't touch my sources file, only added a repo for slack and another one for google earth, but the warning message is about system packages, not third party apps.
Code:chaouche#ychaouche-PC 16:35:35 ~ $ cat /etc/apt/sources.list /etc/apt/sources.list.d/*
#deb cdrom:[Linux Mint 17 _Qiana_ - Release amd64 20140619]/ trusty contrib main non-free
# deb http://archive.getdeb.net/ubuntu trusty-getdeb apps
### THIS FILE IS AUTOMATICALLY CONFIGURED ###
# You may comment out this entry, but any other modifications may be lost.
# deb [arch=amd64] http://dl.google.com/linux/chrome/deb/ stable main
### THIS FILE IS AUTOMATICALLY CONFIGURED ###
# You may comment out this entry, but any other modifications may be lost.
# deb http://dl.google.com/linux/earth/deb/ stable main
### THIS FILE IS AUTOMATICALLY CONFIGURED ###
# You may comment out this entry, but any other modifications may be lost.
# deb http://dl.google.com/linux/talkplugin/deb/ stable main
# Do not edit this file manually, use Software Sources instead.
deb http://packages.linuxmint.com qiana main upstream import #id:linuxmint_main
deb http://extra.linuxmint.com qiana main #id:linuxmint_extra
deb http://archive.ubuntu.com/ubuntu trusty main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu trusty-updates main restricted universe multiverse
deb http://security.ubuntu.com/ubuntu/ trusty-security main restricted universe multiverse
deb http://archive.canonical.com/ubuntu/ trusty partner
# deb http://ppa.launchpad.net/oguzhaninan/stacer/ubuntu trusty main
# deb-src http://ppa.launchpad.net/oguzhaninan/stacer/ubuntu trusty main
# deb http://dl.ajaxplorer.info/repos/apt stable main
# deb-src http://dl.ajaxplorer.info/repos/apt stable main### THIS FILE IS AUTOMATICALLY CONFIGURED ###
# You may comment out this entry, but any other modifications may be lost.
deb https://packagecloud.io/slacktechnologies/slack/debian/ jessie main
# Written by ubuntu-advantage-tools
deb https://esm.ubuntu.com/ubuntu trusty-infra-security main
# deb-src https://esm.ubuntu.com/ubuntu trusty-infra-security main
deb https://esm.ubuntu.com/ubuntu trusty-infra-updates main
# deb-src https://esm.ubuntu.com/ubuntu trusty-infra-updates main
ychaouche#ychaouche-PC 16:35:45 ~ $Any comments ?


This has been a first since I am using mint (2015). I didn't touch my sources file, only added a repo for slack and another one for google earth, but the warning message is about system packages, not third party apps.
Code:chaouche#ychaouche-PC 16:35:35 ~ $ cat /etc/apt/sources.list /etc/apt/sources.list.d/*
#deb cdrom:[Linux Mint 17 _Qiana_ - Release amd64 20140619]/ trusty contrib main non-free
# deb http://archive.getdeb.net/ubuntu trusty-getdeb apps
### THIS FILE IS AUTOMATICALLY CONFIGURED ###
# You may comment out this entry, but any other modifications may be lost.
# deb [arch=amd64] http://dl.google.com/linux/chrome/deb/ stable main
### THIS FILE IS AUTOMATICALLY CONFIGURED ###
# You may comment out this entry, but any other modifications may be lost.
# deb http://dl.google.com/linux/earth/deb/ stable main
### THIS FILE IS AUTOMATICALLY CONFIGURED ###
# You may comment out this entry, but any other modifications may be lost.
# deb http://dl.google.com/linux/talkplugin/deb/ stable main
# Do not edit this file manually, use Software Sources instead.
deb http://packages.linuxmint.com qiana main upstream import #id:linuxmint_main
deb http://extra.linuxmint.com qiana main #id:linuxmint_extra
deb http://archive.ubuntu.com/ubuntu trusty main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu trusty-updates main restricted universe multiverse
deb http://security.ubuntu.com/ubuntu/ trusty-security main restricted universe multiverse
deb http://archive.canonical.com/ubuntu/ trusty partner
# deb http://ppa.launchpad.net/oguzhaninan/stacer/ubuntu trusty main
# deb-src http://ppa.launchpad.net/oguzhaninan/stacer/ubuntu trusty main
# deb http://dl.ajaxplorer.info/repos/apt stable main
# deb-src http://dl.ajaxplorer.info/repos/apt stable main### THIS FILE IS AUTOMATICALLY CONFIGURED ###
# You may comment out this entry, but any other modifications may be lost.
deb https://packagecloud.io/slacktechnologies/slack/debian/ jessie main
# Written by ubuntu-advantage-tools
deb https://esm.ubuntu.com/ubuntu trusty-infra-security main
# deb-src https://esm.ubuntu.com/ubuntu trusty-infra-security main
deb https://esm.ubuntu.com/ubuntu trusty-infra-updates main
# deb-src https://esm.ubuntu.com/ubuntu trusty-infra-updates main
ychaouche#ychaouche-PC 16:35:45 ~ $Any comments ?