AFAIK, the reasons for the warning may be:
If the dependencies have changed on one of the packages you have
installed so that a new package must be installed to perform the
upgrade then that will be listed as "kept-back".
In this case I'd recommend waiting for the dependency to be updated to new version, this would make the "kept back" packages no longer worth keeping back.
Other solutions: dependency is there but was not found
Excerpt from fossfreedom's answer to similar question:
I have found sometimes the package manager cannot cope with the extent of the changes a particular PPA is requesting to be updated.
Package requires dependency, that is perhaps satisfied by other packages (I'm not clear on how different updating tools deal with this, but not all of them find out that package they are yet to install fulfils the dependency of the package currently being installed). Then, you may either:
- do a dangerous
dist-upgrade which may break your distribution,
- or upgrade by hand
apt install list-of-packages-here
- or just get at them one by one:
sudo apt install package1, then package2... (if you want to know which is problematic)
- or use another tool (like
aptitude) to try if it will have that problem
Worth noting that it's Ubuntu 16.04 where
apt-get install can be shortened to
Do you need them?
Taking a look at your kept-back package, I think sometimes you will have precisely the same thoughts as @lpanebr, who purged them (see his answer).
Finally: pinned packages and broken dependencies
There are options for safe upgrades or fixing broken dependencies.
man your-tool-name-here should list them. IIRC it would be
apt install -f packageName or
aptitude --safe-upgrade but I'm not certain.
As for pinned packages - I know there is an option to pin a package, to make it non-updatable. However I've never done this, so can't offer details.