When I tried to upgrade from Ubuntu 14.04 to 16.04, this is the message logs shown after sudo apt-get upgrade. Notice the last line, how do I forcefully update those 961 items?     ..........................................................................    ..........................................................................             xserver-xorg-input-vmmouse-lts-vivid xserver-xorg-input-wacom-lts-vivid          xserver-xorg-lts-vivid xserver-xorg-video-all-lts-vivid          xserver-xorg-video-ati-lts-vivid xserver-xorg-video-cirrus-lts-vivid          xserver-xorg-video-fbdev-lts-vivid xserver-xorg-video-intel-lts-vivid          xserver-xorg-video-mach64-lts-vivid xserver-xorg-video-mga-lts-vivid          xserver-xorg-video-neomagic-lts-vivid xserver-xorg-video-nouveau-lts-vivid          xserver-xorg-video-openchrome-lts-vivid xserver-xorg-video-r128-lts-vivid          xserver-xorg-video-radeon-lts-vivid xserver-xorg-video-savage-lts-vivid          xserver-xorg-video-siliconmotion-lts-vivid          xserver-xorg-video-sisusb-lts-vivid xserver-xorg-video-tdfx-lts-vivid          xserver-xorg-video-trident-lts-vivid xserver-xorg-video-vesa-lts-vivid          xserver-xorg-video-vmware-lts-vivid yelp zeitgeist-core zenity zenity-common        0 upgraded, 0 newly installed, 0 to remove and 961 not upgraded.
How do I upgrade everything on Ubuntu
ubuntu;apt
apt-get upgrade plays it safe: it upgrades all the packages that can be upgraded without breaking other packages. If upgrading package A requires uninstalling package B, apt-get upgrade won't do it, and A ends up in the not upgraded list.Over time, packages get broken into pieces, joined together, renamed, etc. In addition to basic dependencies (A requires B), a package C can declare that it replaces a package B, indicating that when C is installed, it should be ok to uninstall B. Apt also has a concept of automatically-installed vs manually-installed package; it should be ok to remove an automatically-installed package even if it isn't explicitly getting replaced, whereas manually-installed packages are requested by the user and should stay. But apt-get upgrade doesn't take any risk.There is another command apt-get dist-upgrade which is willing to remove packages if necessary. The idea is that apt-get upgrade only upgrades individual packages, whereas apt-get dist-upgrade upgrades the whole distribution. apt-get upgrade is low-risk and you can pretty much do it without paying attention, whereas apt-get dist-upgrade might occasionally remove a program that you rely on, especially if you haven't taken care to mark all the packages you absolutely need as manually installed. You're unlikely to end up with a broken system after apt-get dist-upgrade, but sometimes you might need to reinstall a package or two.Aptitude has the same command duality, but has introduced prefered synonyms:safe-upgrade=upgrade  vs.  full-upgrade=dist-upgrade.In addition, Ubuntu provides a program called do-release-upgrade which is the recommended way to upgrade from one Ubuntu release to the next (or from one Ubuntu LTS to the next). This program runs apt-get dist-upgrade under the hood, but makes some checks and preparations first and performs some cleanup afterwards.In summary: If upgrading between Ubuntu releases, use do-release-upgrade.If you're just installing security updates and bug fixes, use apt-get update followed by apt-get upgrade (or aptitude safe-upgrade).Otherwise use apt-get update followed by apt-get dist-upgrade (or aptitude full-upgrade).