| Frequently Asked Questions |

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# Frequently asked questions

## Table Of Contents

- How complete are the backends?
- Why can't I add or remove software sources
- What's a package catalog?
- Can I include formatting characters in package descriptions?
- Does PackageKit support 1-Click Install?
- How does the command not found functionality work?
- When run as root, gpk-application and pkcon do not work!
- Why is there a session service and and a system service?
- How do I use PackageKit in my application?
- Why don't I get update details with Fedora Rawhide?
- Why doesn't PackageKit work with SELinux?
- What do the tray icons mean?
- What if we don't support percentage updates?
- Why are the remaining times sometimes wildly wrong?
- How will PackageKit support all the different options?
- Error codes are different on each backend?
- Installing packages needs user interaction!
- Does PackageKit replace up2date?
- Is PackageKit a system daemon, always running and using resources?
- How does PackageKit handle dependencies?
- Does PackageKit replace the Red Carpet service?
- How fast is PackageKit?
- How does PackageKit work with multiple users?
- Can users still use their normal package managers?
- What is a Service Pack?
- What is Hughsie's law?
- How do I translate gnome-packagekit?
- Is there an organization sponsoring development of PackageKit?

### How complete are the backends?

Backends do not have to be complete when they are added to PackageKit. If a feature is not present then it is hidden in the UI, which will explain why on some distributions the client tools look a little different to other distributions. You can see the latest feature matrix here.

### Why can't I add or remove software sources?

In the software source viewer you can enable and disable repositories, but you cannot rename, add or remove them. This is a deliberate design choice chosen for the following reasons:

- The mirrorlist and source URL formats are very different between distributions
- There are better ways of adding sources, for instance installing the `repo-release.rpm` package which also adds the GPG keys
- Removing the `repo-release.rpm` removes the repo and any temporary files
- Renaming a repo has no purpose

### What's a package catalog?

There's one use case that I'm very interested in, and that is getting new users with the correct environment to build and start hacking on software or using other software tools. For instance, on www.packagekit.org in the FAQ section, we can have a link to install build files to start hacking on PackageKit.

Now, this `.catalog` file is handled by `gpk-install-catalog` that parses this file and causes the appropriate packages to be installed if they are not already installed. This rocks as we can get GTK+, Xorg hackers up to speed with the minimum of fuss and confusion. It also lets people put links on webpages to install all the stuff you need when writing a How to use a scanner in GIMP howto.

So, what does a .catalog file look like?

    [PackageKit Catalog]

    # Just a package on all versions of fedora that can provide the dependency.
    # If there are multiple packages then the user will be asked to choose
    InstallProvides(fedora)=audio/QCELP

    # Just for Fedora 9, install two development files
    InstallPackages(fedora-9)=glib2-devel;PolicyKit-gnome-devel

    # On any distro, install the package with this file
    InstallFiles=/usr/bin/fontinst

    # For each architecture on Fedora 8, install one of the two different compat files
    InstallFiles(fedora-8-i686)=/usr/lib/pango/1.6.0/modules/pango-arabic-fc.so
    InstallFiles(fedora-8-x64)=/usr/lib64/pango/1.6.0/modules/pango-arabic-fc.so

You'll notice the `distro-id` in between the `()`'s - this lets a packager fine tune the package name, where for instance in Debian the package is called `policykit` and Fedora `PolicyKit`. You can specify a granularity of distribution, distribution-version or distribution-version-architecture - PackageKit will process all the entries that apply. It's of course better to not specify a `()` if possible, as this lets the file work on as many distributions as possible out of the box.

There's also no version checking - intentionally - the distro should be specified and have the correct data. If there's an optional package not in earlier versions then you can do something like this:

    [PackageKit Catalog]

    # Fedora 9 does not have Unique
    InstallPackages(fedora-9)=glib2-devel;PolicyKit-gnome-devel

    # Rawhide is fedora 9.90
    InstallPackages(fedora-9.90)=glib2-devel;PolicyKit-gnome-devel;unique-devel

There's also no description of the catalog that needs translating and verifying - they are just lists of packages, files and provides that might be useful. All the translations come from the distributions metadata, and it's up to the user to verify the package lists that are asked to be installed, so there are no signing or trust issues.

Note: this isn't designed to replace one click install, it just does something that is similar in a different way.

### Can I include formatting characters in package descriptions?

Yes, as long as the descripions are formatted with Markdown then the descriptions will be formatted correctly in client programs. Using Markdown is a deliberate choice as it does not force the vendor to adopt any specific markup language. An example Markdown package description would be:

    GNOME Power Manager uses the information and facilities
    provided by HAL displaying icons and handling user
    callbacks in an **interactive** GNOME session.

    The following *GUI* programs are provided:
    * `gnome-power-preferences` - set policy and change preferences
    * `gnome-power-statistics` - view power graphs and device history

This would be rendered by a text program as:

    GNOME Power Manager uses the information and facilities provided by HAL
    displaying icons and handling user callbacks in an interactive GNOME session.

    The following GUI programs are provided:
    * gnome-power-preferences - set policy and change preferences
    * gnome-power-statistics - view power graphs and device history

A GUI front-end would format the text like this:

GNOME Power Manager uses the information and facilities provided by HAL displaying icons and handling user callbacks in an interactive GNOME session.

The following GUI programs are provided:

- `gnome-power-preferences` - set policy and change preferences
- `gnome-power-statistics` - view power graphs and device history

Update descriptions are also processed for markdown, for example:

### How does the command not found functionality work?

The command not found functionality is a bash extension that allows PackageKit to suggest similar commands, or to offer to install packages to provide commands. It's probably best to click on the image and watch the video.

### Does PackageKit support 1-Click Install?

No, as they are a potential security problem. The issues are as follows:

- That some developer creates a repository with a package with a higher package epoch, and then the distro releases a critical security package (with an updated version, but smaller epoch) and the package does not get upgraded, leaving the user vulnerable.
- The user installs some random repository, where the developer pushes a few svn packages. The developer gets bored, and stop produces updates, and then one of the old packages blocks on the distribution update, causing no further automatic system updates.
- There's no signing of 1-click-install files, so we can't actually be sure that they come from a reputable source.
- There's no localisation in the 1-click-files. For instance, if we only show a French language speaker a description of "remote exploit trojan" they are not going to understand the description.

So what's the solution? Using a standard `$vendor-release.rpm` or `.deb` you can ship the standard repo or source with a signed GPG key. PackageKit also supports catalogs which can install sets of files provided by your distro.

Quoting Sebastian Heinlein, Allowing to easily add third party repositories and install third party software without a certification infrastructure is like opening the gates to hell. Most user just don't have got the technical understanding to handle this well.

### When run as root, `gpk-application` and `pkcon` do not work!

GTK+ tools should not be run as the root user, PERIOD. Any GTK+ program run as the root user is a massive security hole -- GTK+ just isn't designed with this in mind. There are numerous attack vectors when running as root, and programs shouldn't do such insane and insecure things.

Please see the GTK+ explanation for more rationale.

### Why is there a session service and and a system service?

PackageKit runs a process `packagekitd` that is a daemon that runs per-system. The daemon lets you schedule transactions using either the raw DBUS methods, or using libpackagekit. The transactions are very fine grained, so an application would have to manage the transaction process itself. This would mean handling the EULA and GPG callbacks in each application. This is less than ideal.

For this reason, a session helper is provided by the `gpk-update-icon` process which basically makes all the complexity go away; it handles all the GPG key authentication and EULA agreements, and also works with Seahorse and GConf to give some of the settings session persistence. Using the session service is also designed to be synchronous, which means you can send the DBUS call and just wait for the result, rather than managing callbacks to update custom GUIs.

The session helper therefore depends on the shared code in `gpk-update-icon`, but because this is implemented as a DBUS service, can be coded as a QObject for KDE or a simpler object for XFCE or EFL. If you want full integration using custom dialogs without running the extra session process, then use libpackagekit. If you don't care, and just want things to work then use the session interface.

If you want a demo, you can download session.c for a session example and system.c as a system example.

Compile with:

    gcc -o session -Wall session.c `pkg-config --cflags --libs dbus-glib-1`
    gcc -o system -Wall system.c `pkg-config --cflags --libs packagekit-glib`

### How do I use PackageKit in my application?

If you are using GNOME, or running the `gpk-update-icon` then you can use the session dbus interface provided by this process. If you are not using GNOME, or choose to not use the `gpk-update-icon` applet then you can use an alternate interface provided by your desktop.

Using this shared session service you can use the following DBUS methods to make PackageKit just do the right thing. All the additional confirmation, package downloads, GPG and EULA prompting is done automatically.

The DBUS methods are designed to be run syncronously, but can be run async using `dbus_g_proxy_begin_call` and then returning on the `DBusGProxyCallNotify`.

For example, the following code snippet would install a package by name:

    #include <dbus/dbus-glib.h>

    DBusGConnection *connection;
    DBusGProxy *proxy;
    GError *error = NULL;
    gboolean ret;

    connection = dbus_g_bus_get (DBUS_BUS_SESSION, NULL);
    proxy = dbus_g_proxy_new_for_name (connection,
                                 "org.freedesktop.PackageKit",
                                 "/org/freedesktop/PackageKit",
                                 "org.freedesktop.PackageKit.Modify");
    /* execute sync method */
    ret = dbus_g_proxy_call (proxy, "InstallPackageNames", &error,
                             G_TYPE_STRV, {"openoffice-clipart", NULL},
                             G_TYPE_STRING, "",
                             G_TYPE_INVALID, G_TYPE_INVALID);
    if (!ret) {
            g_warning ("failed: %s", error->message);
            g_error_free (error);
    }

or in python...

    import dbus

    try:
        bus = dbus.SessionBus()
    except dbus.DBusException, e:
        print 'Unable to connect to dbus: %s' % str(e)
        sys.exit()
    try:
        proxy = bus.get_object('org.freedesktop.PackageKit', '/org/freedesktop/PackageKit')
        iface = dbus.Interface(proxy, 'org.freedesktop.PackageKit')
        iface.InstallPackageName('openoffice-clipart')
    except dbus.DBusException, e:
        print 'Unable to use PackageKit: %s' % str(e)

The methods available on this interface are:

- `InstallPackageName("openoffice-clipart")`
- `InstallProvideFile("/usr/share/fonts/sarai/Sarai_07.ttf")`
- `InstallLocalFile("/home/dave/Desktop/lirc-0.6.6-4.rhfc1.dag.i686.rpm")`
- `InstallMimeType("application/x-rpm")`
- `InstallFont("lang(en_GB)")`

Please email me or the mailing list if you have any other questions

### What do the tray icons mean?

| Bugfix update |  | Enhancement update |  | High priority update
| Low priority update |  | Normal update |  | Security update

NOTE:Not all the icons may show for some backends.

If you are using Fedora rawhide then only the bugfix icon will be show due to missing metadata. In the released versions of Fedora metadata is added to updates and the type of update can be found.

### Why don't I get update details with Fedora Rawhide?

The Rawhide repository does not supply metadata needed for the update-viewer to display extra information about the update, such as changelogs, CVE and bugzilla references. Only released versions of Fedora have this metadata.

### Why doesn't PackageKit work with SELinux?

The process `packagekitd` is not recognized by SELinux if you are using old selinux-policy rules. Until the policy is updated to handle system activation, you'll have to run in permissive mode, rather than enforcing.

See Red Hat Bugzilla for further information.

### What if the backend package manager doesn't support percentage updates?

You don't have to have a backend that supports percentage updates. If you don't know the progress, just emit NoPercentageUpdates and then the UI should just do the right thing and spin backwards and forwards.

### Why are the remaining times sometimes not present or wildly wrong?

The remaining time to completion of the transaction is calculated using an average time of the time between percentage updates points, extrapolated to 100%. This means that backends that give accurate and frequent percentage-changed signals will get accurate times.

If a backend updates the percentage using very course updates (e.g. 20%, 40%, 60%, 80%, 100%) then the remaining time algorithm will not perform well. Similarly, if the duration of 0% to 50% takes 2 minutes and 50% to 100% takes 10 minutes then at first the time will be reported under the true time to completion. It is up to the backends to map the transaction progress to fine-granularity accurate percentage updates, at least as best as possible.

### With all the differences between backends, how will PackageKit support all the different options?

Backends don't have to support all options of all methods. Just set an error and return false if not implemented.

### But error codes are different on each backend?

Error codes have to be standardized so they can be localized. The error detail field can just be the untranslatable output. If you are creating a backend and you need another error enum, mention it and we can add it to the supported list.

### How will PackageKit handle installation an application that needs user interaction?

Upgrading, installing or removing packages has to be 100% silent.

The user cannot be prompted mid-transaction for questions as these will not be handled in PackageKit. The backend should do the right thing, as these questions mean very little to the average user.

The reasons for this are as follows:

- The messages cannot be translated as the daemon is running in the C locale, and there may be multiple running session clients in different locales.
- Stopping the transaction and waiting for input would also mean the methods are no longer "fire and forget".
- Security updates can now be performed automatically, i.e. when the user is idle. There's no user at the console in this case to answer questions.
- Due to the client/server split of PackageKit, a non-root user would be able to change the answer of debconf scripts, and another PolicyKit role would have to be defined. In this case a situation could arise where a user is able to update software, but not agree to EULAs, thus making the transaction invalid and impossible.

EULAs or other agreements will have to be agreed to before the transaction is processed using the `EulaRequired` signal. EULAs should preferably be shown per-user - i.e. the first time an application is run.

PackageKit will not install packages with broken maintainer scripts that require a stdin. Debian policy clearly says that prompting on `stdin` instead of using debconf is deprecated. If this is attempted the backend should detect this and error out of the transaction with `PK_ERROR_ENUM_BROKEN_PACKAGE`. We cannot and will not ask the user for random standard input.

See the Debian PackageKit wiki for more details and further discussion.

If the transaction needs to tell the user something, the `Message()` method can be used that will localise the message up the stack, and also give the user a way of ignoring duplicate messages of this type. We really don't what to be doing things like this or this.

### Does PackageKit replace up2date?

PackageKit does not replace up2date. PackageKit is a way for users to interact with the packaging system, not for an administrator to install software on remote machines.

### Is PackageKit a system daemon, always running and using resources?

PackageKit is not yet another system daemon. It quits when not doing anything, and only starts when something wants information or a task completed.

### How does PackageKit handle dependencies?

PackageKit does not do dependency resolution. This problem has already been solved by the backend systems and we don't really want to re-invent the wheel.

PackageKit does not have the fine-grained API to do everything. For instance, synaptic should still use libapt as can do much more than can be provided by PackageKit.

### Does PackageKit replace the Red Carpet service?

PackageKit is not a replacement to red carpet. Red carpet was really great and years ahead of it's time, but tried to do everything package related on the system, and moved onto the enterprise centralized management model. Although cool, this latter point made things too political in my opinion.

### How fast is PackageKit?

PackageKit is really fast. It takes about 1 second to search for installed and available packages with "power" in the description - no blocking of the UI happens at all as it's all asynchronous. All the applications start instantly with no root password needed at startup.

### How does PackageKit work with multiple users?

PackageKit is designed from the ground up to work with fast user switching and logging in and out of sessions during upgrades. You can start a system upgrade, log out, log in as another user, and be notified when the upgrade is complete, all without risking your rpmdb.

### Can users still use their normal package managers and backends, such as Yum, APT or Conary?

PackageKit does not stop you using the low level tools yourself. You can use rpm and yum or dpkg and apt when PK is inactive (99.999% of the time) when you really need some command line love. No more fighting over `yum`, `yum-updatesd`, `pup` and `pirut`.

### What is a Service Pack?

A service pack is a tarball which contains the particular package and its dependencies. The user can select the dependencies to be packed using the --with-package-list option. Along with the dependencies, a service pack has a file named metadata.conf which contains the distribution name and version and the date of creation of the pack. Service packs are generated using the command line client `pkgenpack`.

### What is Hughsie's law?

A joke that started on IRC late one night in '07. Put formally it is: Authentication or license prompts can only be done before the transaction has started, and messages or notices about the transaction can only be shown after the transaction has completed.

### How do I translate gnome-packagekit?

See the GNOME Translation Team web pages for how to contribute to GNOME localisation.

### Is there an organization or corporation sponsoring development of PackageKit?

PackageKit is not sponsored by anyone. Whilst interning at Red Hat in '07 I spent a few days on the API and some UI designs, but all the coding is done in my free time. I now work at Red Hat full time.

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