always wondered about why some packages are held back by the Update Manager? These are mostly core components, we the Linux kernel. If you want the update still does the following: sudo apt-get
update & & sudo apt-get dist-upgrade
However, remember that such components are not held back completely groundless, that they are indeed released for the Update, but since it is such an important component, may still have problems due to interactions (eg kernel modules no longer work and must be recompiled) occur.