My first reaction to PackageKit UI was negative after its initial release on Fedora. It was prejudice at first sight. I did not see any advantage in reinventing the wheel. The only GUI package manager I used was Synaptic on Ubuntu. Usually the GUI package managers seemed to be too limiting and, besides, “yum -y update” is hardly a problem to remember. Even searching for packages via yum was not a problem. Using pacman or apt is equally easy.
I did not see the need to unify the backends of package managers. For all practical purposes, only rpm or dpkg formats mattered and there seemed to be little reason for someone to create one more. Users of distributions like Gentoo, Arch Linux were not particularly interested in a GUI front end for their package management applications.
Even the controversy which arose with a proposed change in the package installation policy of Fedora 12 (https://bugzilla.redhat.com/show_bug.cgi?id=534047) did not raise a doubt in my mind that there was something more to PackageKit than I had assumed. I continued to ignore PackageKit.
While I would have loved greater simplicity in package management, the solutions from various distributions seemed to be simplistic GUIs. Had Synaptic been integrated into Fedora, I would have been far happier.
It was while trying to understand how PolicyKit framework was being integrated into the distributions that I realised that I had misunderstood PackageKit very badly.
My new understanding was that it was not a reinvention of the wheel but rather an approach to the same issue from a different perspective. The philosophy of PolicyKit is that the user interface should not run in a privileged mode. This goes against the common assumption that package management should require administrative privileges. Hence, an application like Synaptic runs as a superuser. If the PolicyKit framework is to be used, package management applications must be split into a server and a client. The server will be a privileged application which will use PolicyKit framework and D-Bus to control access rights. The client application just does not worry about access controls at all. The access controls will be managed by policy files and PolicyKit framework.
We can go a step further and recognise that the core operations required of a package management server are the same or similar. Implementation details differ. Hence, instead of creating a PackageKit server only for yum, it would be better to define a common interface for the client. That is, rather than recreate functionality of yum or extend yum to support PolicyKit, a separate PackageKit server is written which then has a thin layer for talking to yum or apt or whatever may be the case.
Unfortunately, what we as users saw was the GUI which was disappointing. However, nothing prevents Synaptic-like application to use the PackageKit server and appeal to a different set of audience.
Implications are obvious. Which set of operations can be done by whom can be determined by the owner of the system. Package managers can offer a default policy, which may be modified by the distribution developers and which may finally be modified by the administrator of the system.
The default policy is available in /usr/share/polkit-1/actions/org.freedesktop.packagekit.policy. If the default is over-ridden by the distribution, it will be available in /var/lib/polkit-1/localauthority/10-vendor.d. The default policy requires administrative privileges on the active console to be able to install any applications. I could not install an application or update the system using the GUI application from a diskless workstation!
However, updating a system can be done by any active console user, a fact I had not noticed as I was relying only on yum to keep my system current.
You can find the various actions and the default access controls in the org.freedesktop.packagekit.policy file mentioned above.
An interesting option would be to integrate PackageKit server with pacman for Arch Linux instead of minimal functionality with ALPM as at present.
What about Ubuntu? Here's an indication from the main page of Software Center, the new package management application for Ubuntu.
“Ubuntu Software Center is implemented using Python, GTK, and Aptdaemon, and may use PackageKit for some components. “
I am not inclined to give up using yum (or pacman) and use the GUI instead. However, my appreciation of what is being done with PackageKit has gone up. If Synaptic is modified to work with PackageKit server, I may even switch to the GUI.
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