Package upgrade command

[Lian Liming <lianliming@gmail.com>]

Hi all,

   To upgrade the package, I have two way:
   "aptitude update" and then "aptitude upgrade",
   or "aptitude update" and then "aptitude dist-upgrade".

   So what is main difference between the two parameters
"upgrade" and "dist-upgrade" for command "aptitude"? and which is
recommended on Debian/Unstable?
 
   Thanks in advance!
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