I’ve upgraded to Linux 16.04, but when running the third line, it says “the packages have been kept back”. (See the details below)
makara@makara-VirtualBox:~$ sudo apt-get upgrade
Reading package lists… Done
Building dependency tree
Reading state information… Done
Calculating upgrade… Done
The following packages were automatically installed and are no longer required:
linux-headers-4.4.0-72 linux-headers-4.4.0-72-generic linux-image-4.4.0-72-generic linux-image-extra-4.4.0-72-generic
Use ‘sudo apt autoremove’ to remove them.
The following packages have been kept back:
libparse-debianchangelog-perl onboard onboard-data
0 upgraded, 0 newly installed, 0 to remove and 3 not upgraded.