~ubuntu-core-dev/update-notifier/ubuntu

After certain upgrades (most notably upgrades between Ubuntu

releases), there are follow-up actions which should be taken by the

user. These are not logically part of the upgrade, but should be dealt

with at some point after the upgrade is complete.

A prime example is the UTF8MigrationTool. During an upgrade from

WartyWarthog to HoaryHedgehog, the system will be configured such that

UTF-8 encoding is available, and will be expected by applications per

default. The user should switch to a UTF-8 locale, and possibly rename

or re-encode files in order to achieve the best user experience. These

things cannot be done in automated fashion during the upgrade, but

must instead be dealt with interactively by the user.

Another example is the reboot notification. Packages like the kernel,

glibc, dbus and hal require a reboot. To simplify things

update-notifier installs a helper script in

/usr/share/update-notifier/notify-reboot-required

that can be called in the packages postinst script (make sure to check

for it first). It is i18n-able via langpacks and it will only be shown

once.  

Design:

 * Maintainer scripts create/copy a notification to

   /var/lib/update-notifier/user.d

 * update-notifier checks for those after each apt invocation (when

   /var/lib/update-notifier/dpkg-was-run changed) and notifies the user

   that they are pending

 * When the user selects to process pending actions, they are executed

   in sequence within the context of the user and the desktop (and so

   can display a GUI, interact with the user, etc.)

Details:

 * the directory /var/lib/update-notifier/user.d/ is used to store hooks

 * a hook file looks follows rfc822 rules:

   - a fieldname may have a "-$locale" in it. This is for i18n.

   - if "GettextDomain" is found, dgettext() will also be tried to get a

     i18n string (for langpacks)

   - each hook must have a unique "Name" key and a "Description" key

   - a optional "Priority" with {crititcal, high, medium, low} that

     gives the user a idea how importend the hook is (currently not used) 

   - a optional "Command" field may be registered with a shell-command

     that the user can run (e.g. a script like /usr/share/package/do-something)

   - a optional "Terminal: True" field if the command should be

     execute in a terminal

   - update-notifier uses inotify to monitor

     /var/lib/update-notifier/dpkg-was-run and

     /var/lib/update-notifier/user.d/ and show a small information icon for

     hooks it has not seen yet

   - when the user clicks on the icon the name and description is

     given. If a shell script is registered a button is displayed that will

     run the script. the description in the hook should explain what the

     script will do

   - the encoding of the i18n fields is UTF-8

   - the optional key "DontShowAfterReboot" will make sure that the 

     notification is not shown when the system rebootet since it was 

     created/refreshed 

   - the optional key "DisplayIf" will run a shell command (system())

     to figure out if the note should be displayed or not. If the command

     returns 0 the note will be displayed, otherwise it will be ignored

   - the optional key "OnlyAdminUsers" controls if the note is shown to all

     users or only to the admin users (users in the admin group). the

     default is "OnlyAdminsUsers=true".

Example

Name: The great UTF-8 Migration

Name-de_DE: Die grosse UTF-8 Migration

Priority: Medium

Command: utf8-migration-assistant

Terminal: True

GettextDomain: utf8-migration-assistant

DisplayIf: shell-command

OnlyAdminUsers: False

Description: This command will convert your stuff into UTF-8.

 Use this command if you want a working gnome desktop and you

 feel the world should be a better place.