sudo apt-get upgrade 不升级某些软件包

Question

sudo apt-get upgrade 不升级软件包

hp@hp-HP-15-Notebook-PC:~$ 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:
  libnss3 openjdk-7-jdk openjdk-7-jre openjdk-7-jre-headless thunderbird
  thunderbird-gnome-support
0 upgraded, 0 newly installed, 0 to remove and 6 not upgraded.
hp@hp-HP-15-Notebook-PC:~$