If you used the instructions at this post to update your Ubuntu Linux packages, basically, apply patches, you get the following message at times:
The following packages have been kept back:
<list of packages>
This basically prevents the packages listed from getting updated. To overcome this issue, there are two ways:
sudo apt-get dist-upgrade <enter> in a terminal window, OR;
2. Start Update Manager and update the packages from there.
I prefer the second option.