Do you need to reboot your ubuntu ?

Just check for the existence of this file after an update:

don@etiikka:~$ ls -al /var/run/reboot-required
-rw-r--r-- 1 root root 32 Oct  9 15:17 /var/run/reboot-required

If it is there, you need to restart the machine -- at the command line, do this:

don@etiikka:~$ sudo reboot