apt-get not updating GUI packages?

[Hylton Conacher (ZR1HPC)]

Hi,

I run Ubuntu 16.04 as a Dovecot mailserver and to keep the system 
patched am religiously using ssh to sign into the machine and run both 
of the following commands:
$ sudo apt-get update
$ sudo apt-get upgrade with an occasional $ sudo apt autoremove

On both previous incidents where I was told after signing in that there 
were updates available, I ran the above commands.
Afterwards I reboot the machine using sudo and then sign-in again via 
SSH to check if more updates are available.

Below is a screen paste
******
Welcome to Ubuntu 16.04.4 LTS (GNU/Linux 4.4.0-121-generic x86_64)

  * Documentation:  https://help.ubuntu.com
  * Management:     https://landscape.canonical.com
  * Support:        https://ubuntu.com/advantage

   System information as of Mon Apr 30 16:00:41 SAST 2018

   System load:  0.44               Processes:           173
   Usage of /:   35.6% of 46.64GB   Users logged in:     0
   Memory usage: 1%                 IP address for eth0: xxx.xxx.x.xx
   Swap usage:   0%

   Graph this data and manage this system at:
     https://landscape.canonical.com/

10 packages can be updated.
0 updates are security updates.

You have mail.
Last login: Mon Apr 30 15:55:31 2018 from 192.168.0.10

So given that there are updates I run:
hylton at machine:~$ sudo apt-get update
[sudo] password for hylton:
Get:1 http://security.ubuntu.com/ubuntu xenial-security InRelease [107 kB]
Hit:2 http://ppa.launchpad.net/kubuntu-ppa/backports/ubuntu xenial 
InRelease
Hit:3 http://us.archive.ubuntu.com/ubuntu xenial InRelease 

Hit:4 http://us.archive.ubuntu.com/ubuntu xenial-updates InRelease 

Hit:5 http://us.archive.ubuntu.com/ubuntu xenial-backports InRelease
Fetched 107 kB in 1s (73.7 kB/s)
Reading package lists... Done
hylton at machine:~$ sudo apt-get upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following packages have been kept back:
   linux-generic linux-headers-generic linux-image-generic 
linux-signed-generic
   linux-signed-image-generic
0 upgraded, 0 newly installed, 0 to remove and 5 not upgraded.
hylton at machine:~$

******
Both times the information blurb on Ubuntu tells me there are still the 
same number of packages to be updated. Asides from this the blurb said 
10 packages needed updating yet the upgrade command said only 5 would 
not be upgraded?

Looking at the man page for apt-get it indicates that apt-get is the 
workhorse behind GUI package managers i.e. Synaptic.

However if I log onto the machine GUI and select Synaptic I can install 
the 5 packages that were kept back by apt-get?

Two questions:
1. Why does the blurb indicate there are 10 packages need updating yet 
the upgrade only indicates 5, which end up being held back and needing 
to be installed using a GUI package manager?
2. Is there a switch I am missing on the commands to install GUI 
packages from the CLI as apt-get, being the workhorse it is supposed to 
be isn't working very hard as it's leaving what seems to be kernel 
updates to the GUI package manager which probably uses apt-get in the 
background anyway.

Regards
Hylton
P.S: I am a subscriber to the mailing list

exit my SSH session