Clarification wanted on apt upgrade/update and synaptic etc.

[Jensen Somers]

Chris G wrote:
> I'm moving (probably) to Ubuntu from Fedora.  I'm installing Ubuntu on
> new hardware leaving my Fedora system on the old hardware until I can
> rely on the new system.  

Welcome.

> 
> I'm a mostly command line person (at work I'm a developer on Sun
> Solaris 'legacy' systems), I cut my Linux teeth on Slackware.  Thus I
> tend to use the command line in preference to GUI.
> 
> I have installed Ubuntu 8.10 beta on my new system knowing that by the
> time I have decided to rely on it 8.10 will have been released. I understand
> the fundamentals of what apt/synaptic are doing (having used yum/rpm for
> a while) but I'm still feeling my way a bit as regards the details of what's
> going on. Now on to my questions:-
> 
>     What does 'apt-get update' do?  Is it just updating my local copy
>     of the distribution lists to the latest versions of available
>     software? 

Update is used to resynchronize the package index files from their 
sources. The indexes of available packages are fetched from the 
location(s) specified in /etc/apt/sources.list. For example, when using 
a Debian archive, this command retrieves and scans the Packages.gz 
files, so that information about new and updated packages is available. 
An update should always be performed before an upgrade or dist-upgrade. 
Please be aware that the overall progress meter will be incorrect as the 
size of the package files cannot be known in advance.

I always believed 'refresh' was a better word in stead of 'update'.

> 
>     If I do 'apt-get upgrade' will it do (have done?) an update of the
>     file lists automatically?  Is there some sort of algorithm used to
>     decide when an 'update' is required?

Upgrade is used to install the newest versions of all packages currently 
installed on the system from the sources enumerated in 
/etc/apt/sources.list. Packages currently installed with new versions 
available are retrieved and upgraded; under no circumstances are 
currently installed packages removed, or packages not already installed 
retrieved and installed. New versions of currently installed packages 
that cannot be upgraded without changing the install status of another 
package will be left at their current version. An update must be 
performed first so that apt-get knows that new versions of packages are 
available.

Basically it just checks version information. I don't think any fancy 
algorithms are used for that.

> 
>     When the GUI (from gnome-panel) pops up and tells me that upgrades
>     are available is it taking me to the 'same place' as I will get to
>     by doing 'apt-get upgrade'?  It seems to take much less time, is
>     this because it has already done some of the work in the
>     background? 

It's the same thing and should take as much time as the command line 
version. The only difference is that it doesn't necessarily writes any 
debug output to your screen, which is something that adds up to the 
total time.

> 
>     If I keep upgrading my 8.10 beta will it become the 8.10 release
>     version in due course or do I need to take any special actions to
>     achieve this?
> 

Yes, it just moves along and no extra steps are required.

- Jensen