Apt-get upgrade & dist-upgrade - Différence ?

[Domi <cdominic at free dot fr>]

Question:

je pratique régulièremet apt-get upgrade...mais pas dist-upgrade....

voici ce que le retour console :

domi at breizhiz:~$ su -
Password:
breizhiz:~# apt-get dist-upgrade
Reading Package Lists... Done
Building Dependency Tree... Done
Calculating Upgrade... Done
The following packages will be REMOVED:
 mozilla-firefox-locale-fr
The following NEW packages will be installed:
 desktop-file-utils libflac++4 libreadline5 sudo
The following packages will be upgraded:
 dialog gksu jackd k3b k3blibs libgda2-1 libgda2-common libgnomevfs2-0
 libgnomevfs2-common libidn11 libjack0.80.0-0 liboggflac1 mozilla-firefox
 vorbis-tools
14 upgraded, 4 newly installed, 1 to remove and 0 not upgraded.
Need to get 15.4MB of archives.
After unpacking 919kB of additional disk space will be used.
Do you want to continue? [Y/n]

Ma question est la suivante, le fichier "mozilla-firefox-locale-fr" va 
être effacer !...
Il me faudra donc le réinstaller.... pour le reste je sais pas...en bref 
quel est l'utilité de "dist-upgrade"
par rapport à "upgrade".

Merci

Domi