Setting User Preferences with Mission Control Desktop

A challenge with software

Managing software for thousands of users presents a formidable challenge to the system administrator. Publishing corporate policy, using standard environments and providing clear end-user documentation helps. However, it doesn’t beat automatically doing it right.  This is the power of MCD autoconfig.

In an earlier post, I introduced MCD as a way to configure Mozilla products (Firefox, Thunderbird, Prism, etc) and provided background on building them with autoconfig support.  This post covers how to get started with the standard javascript API.  In forthcoming posts I’ll detail the useful enhancements I built using this API.

The environment

First, a quick rehash of my world.  I work in a Solaris shop with over 33,000 users.  Supported users log into a shared Sun Ray server or their personal workstation which mounts a shared NFS directory.  That directory houses the software I support along with about 700 other programs.

While this post is unix-centric, other operating environments that launch managed software can make use of MCD. See the introductory post for  a little more detail.

Mozilla Preference System

Firefox and Thunderbird use a simple preference tree to store all configuration options. Leaves of the tree are strings that store the option’s value.  For example, the preference browser.startup.homepage is a string containing the URL(s) of Firefox’s homepage.  mail.forward_message_mode contains an integer indicating how Thunderbird should forward email messages (inline or as an attachment).  You can find every available setting and their values in the config editor for Thunderbird and about:config in Firefox.

When a user changes his or her preferences the changed values are stored in a file called prefs.js in their home directory. On my MacOS laptop, this is $HOME/Library/Application Support/Firefox/Profiles/kzssiknu.default.

The Application Programming Interface

The autoconfig acts on preferences through a javascript API defined in the file MOZILLA_LIB_DIR/defaults/autoconfig/prefcalls.js.  I will talk about the most useful in this post and cover the LDAP parts of the API later.

// Used most often
function defaultPref(prefName, value);
function lockPref(prefName, value);
// Sometimes used
function displayError(funcname, message);
function getenv(name);

defaultPref() and lockPref()

These two functions perform the bulk of work in an autoconfig script.  A default preference setting may be overridden by the user, but a locked preference may not.

getenv() and displayError()

getenv() acts as you would expect from its name. This function returns the value of an environment variable.  I use it to get $USER and $HOME. displayError() pops up an error message.  It is useful for debugging, but a user should rarely see it.

Putting it all together

We now have some basic building blocks to configure thousands of users. Here is a look at a simple autoconfig.js file for Firefox.  These settings will apply to every user.

// Catch errors
   // Set  downloads directory to a folder on the user's desktop
   var download_dir = getenv("HOME") + "/Desktop/Downloads";
   defaultPref("", download_dir);
   defaultPref("", download_dir);
   defaultPref("", download_dir);
   defaultPref("", 2);kk
   // Length of Time to Remember Visited Pages For (Days) - 30
   defaultPref("browser.history_expire_days", 30);
   // Automatically Add 'www.' and '.com' to the Location if a Web Page is Not Found - Enabled
   defaultPref("browser.fixup.alternate.enabled", true);
   // Lock the cache size to 60MB for shared performance
   lockPref("browser.cache.memory.capacity", 60000);
   lockPref("browser.cache.disk.capacity", 60000);
   // fix memory usage with lots of tabs
   lockPref("browser.sessionhistory.max_total_viewers", 2);
   // Set animated images to loop once
   defaultPref("image.animation_mode", "once");
} catch(e)
   displayError("autoconfig.js failed", e);

Learning preference strings

Finding the right preference setting or combination of preferences that change the program’s behavior sometimes presents a challenge.  I use the About:config entries page on the Mozilla Zine knowledge base.  That page also has a pointer to three more resources.

Another technique is to watch your own prefs.js file for changes when you twiddle settings.  Save a copy of prefs.js before flipping a preference.  Immediately quit the application after the change and diff the two files.

[Edit: I wrote up an entire post on this subject.]

Using LDAP and more fun things to do

In following posts I will cover retrieving information from LDAP, better error reporting, reading local files like $HOME/.printers, and simplifying Thunderbird email account management. Stay tuned.

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