Cheatsheet: Master Linux Package Management, spawned a LinuxChix discussion of the subtleties of Debian package management (which includes other Debian-based distros such as Ubuntu, Knoppix etc.) Specifically, we were unclear on the differences among apt-get upgrade or dist-upgrade, aptitude upgrade, aptitude dist-upgrade, and aptitude -f dist-upgrade. Most of us have just been typing whichever command we learned first, without understanding the trade-offs.
But Erinn Clark, our Debian Diva, checked with some of her fellow Debian experts and got us most of the answers, which I will attempt to summarize with a little extra help from web references and man pages.
First, apt-get vs. aptitude: we were told that the primary difference between them is that "aptitude is less likely to remove packages." I confess I'm still not entirely clear on what that means, but aptitude is seen as safer and smarter and I'll go on using it.
aptitude upgrade gets updates (security, bug fixes or whatever) to all currently installed packages. No packages will be removed, and no new packages will be installed. If a currently installed package changes to require a new package that isn't installed, upgrade will refuse to update those packages (they will be "kept back"). To install the "kept back" packages with their dependencies, you can use:
aptitude dist-upgrade gets updates to the currently installed packages, including any new packages which are now required. But sometimes you'll encounter problems in the dependencies, in which case it will suggest that you:
aptitude -f dist-upgrade tries to "fix broken packages", packages with broken dependencies. What sort of broken dependencies? Well, for example, if one of the new packages conflicts with another installed package, it will offer to remove the conflicting package. Without -f, all you get is that a package will be "held back" for unspecified reasons, and you have to go probing with commands like aptitude -u install pkgname or apt-get -o Debug::pkgProblemResolver=yes dist-upgrade to find out the reason.
The upshot is that if you want everything to just happen in one step without pestering you, use aptitude -f dist-upgrade; if you want to be cautious and think things through at each step, use aptitude upgrade and be willing to type the stronger commands when it runs into trouble.
Sections 6.2 and 6.3 of the Debian Reference cover these commands a little, but not in much detail. The APT Howto is better, and runs through some useful examples (which I used to try to understand what -f does).
Thanks go to Erinn, Ari Pollak, and Martin Krafft (whose highly rated book, The Debian System: Concepts and Techniques, apparently would have answered these questions, and I'll be checking it out).
[ 22:19 Mar 14, 2007 More linux | permalink to this entry | ]