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HOWTOs: The Debian Sandwich Part II Posted on Monday, April 02 @ 21:36:20 BST
Welcome to the second part of The Debian Sandwich, I received so much glory and praise from the first part so I decided I thought I ought to write a sequel.
Before we delve into the mysteries of dpkg which this article is mostly concerned with let me lead you through the reasoning behind The Debian Sandwich. This metaphor relates to the fact that in the Debian package system there are three layers, your highest level (which is the top slice of bread) is your favourite apt front end dselect/gnome-apt/kapt ( does this exist or am I imaging it?), the next layer in the sandwich is apt itself, this is the filling (Bacon, Lettuce and Tomato for me 🙂 ), the front end programs control apt. You can of course run apt yourself and many people do (including me!), apt is itself a wrapper for the lowest layer, dpkg, which is the bottom layer in the sandwich . Dpkg is a complex beast of which we are only going to scratch the surface of, it is unlikely that you will need to use dpkg much, it is mainly used to build new packages and those from source through its variants dpkg-deb, dpkg-buildpackage, dpkg-source (there are lots, typing dpkg and then using the auto complete feature of your shell (if it has one) will reveal them).
We will just cover the basic and most useful features, of dpkg. If you want more in depth knowledge the man page provides an excellent source of information. I strongly recommend that you use apt as a wrapper for dpkg wherever possible. The only times you will not be able to use apt is if you have a stand alone deb file that you wish to install or if you want to remove a specific package without affecting dependencies etc through the use of --force-thing.
The basic options available for dpkg are:
dpkg -i | --install filename(s) - this command simply installs the given package file. Note: it takes the FULL path to the file not just the package name. If the package is already installed it upgrades it to this version
dpkg -r | --remove packagename(s) - this command removes a package leaving any configuration files. Note: it takes the package name NOT the path to the file.
dpkg -P | --purge packagename(s) - this command does the same as above but removes the configuration files also
dpkg -s | --status packagename(s) - check the status of specified packages, see the man page for a full list but these include, installed, half-configured etc.
dpkg -C | --audit - this is a very useful it checks all the installed packages on your system to look for broken packages, useful one to run in a crontab perhaps
dpkg -L | --listfilespackagename(s) - list files belonging to specified package(s)
dpkg -S | --searchpattern - list the package(s) owning files that match pattern
Thats about all the important commands there is just one option I think is important to mention and that is --force-thing, this allows you to override certain aspects of the packaging system for the command you are executing, for a full list of possible options do --force-help, but the only one i've ever used is --force-depends which turns all dependency problems into warnings.
I hope you enjoyed this sequel, if you have any comments why not make them below