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   1  This document is intended to provide useful advice for parties seeking to
   2  redistribute MediaWiki to end users.  It's targeted particularly at maintainers
   3  for Linux distributions, since it's been observed that distribution packages of
   4  MediaWiki often break.  We've consistently had to recommend that users seeking
   5  support use official tarballs instead of their distribution's packages, and
   6  this often solves whatever problem the user is having.  It would be nice if
   7  this could change.
   8  
   9  == Background: why web applications are different ==
  10  
  11  MediaWiki is intended to be usable on any web host that provides support for
  12  PHP and a database.  Many users of low-end shared hosting have very limited
  13  access to their machine: often only FTP access to some subdirectory of the web
  14  root.  Support for these users entails several restrictions, such as:
  15  
  16    1) We cannot require installation of any files outside the web root.  Few of
  17    our users have access to directories like /usr or /etc.
  18    2) We cannot require the ability to run any utility on the command line.
  19    Many shared hosts have exec() and similar PHP functions disabled.
  20    3) We cannot assume that the software has write access anywhere useful.  The
  21    user account that MediaWiki (including its installer) runs under is often
  22    different from the account the user used to upload the files, and we might be
  23    restricted by PHP settings such as safe mode or open_basedir.
  24    4) We cannot assume that the software even has read access anywhere useful.
  25    Many shared hosts run all users' web applications under the same user, so
  26    they can't rely on Unix permissions, and must forbid reads to even standard
  27    directories like /tmp lest users read each others' files.
  28    5) We cannot assume that the user has the ability to install or run any
  29    programs not written as web-accessible PHP scripts.
  30  
  31  Since anything that works on cheap shared hosting will work if you have shell
  32  or root access too, MediaWiki's design is based around catering to the lowest
  33  common denominator.  Although we support higher-end setups as well (like
  34  Wikipedia!), the way many things work by default is tailored toward shared
  35  hosting.  These defaults are unconventional from the point of view of normal
  36  (non-web) applications -- they might conflict with distributors' policies, and
  37  they certainly aren't ideal for someone who's installing MediaWiki as root.
  38  
  39  == Directory structure ==
  40  
  41  Because of constraint (1) above, MediaWiki does not conform to normal
  42  Unix filesystem layout.  Hopefully we'll offer direct support for standard
  43  layouts in the future, but for now *any change to the location of files is
  44  unsupported*.  Moving things and leaving symlinks will *probably* not break
  45  anything, but it is *strongly* advised not to try any more intrusive changes to
  46  get MediaWiki to conform more closely to your filesystem hierarchy.  Any such
  47  attempt will almost certainly result in unnecessary bugs.
  48  
  49  The standard recommended location to install MediaWiki, relative to the web
  50  root, is /w (so, e.g., /var/www/w).  Rewrite rules can then be used to enable
  51  "pretty URLs" like /wiki/Article instead of /w/index.php?title=Article.  (This
  52  is the convention Wikipedia uses.)  In theory, it should be possible to enable
  53  the appropriate rewrite rules by default, if you can reconfigure the web
  54  server, but you'd need to alter LocalSettings.php too.  See
  55  <https://www.mediawiki.org/wiki/Manual:Short_URL> for details on short URLs.
  56  
  57  If you really must mess around with the directory structure, note that the
  58  following files *must* all be web-accessible for MediaWiki to function
  59  correctly:
  60  
  61    * api.php, img_auth.php, index.php, load.php, opensearch_desc.php, thumb.php,
  62    profileinfo.php, redirect.php, trackback.php.  These are the entry points for
  63    normal usage.  This list may be incomplete and is subject to change.
  64    * mw-config/index.php: Used for web-based installation (sets up the database,
  65    prompts for the name of the wiki, etc.).
  66    * images/: Used for uploaded files.  This could be somewhere else if
  67    $wgUploadDirectory and $wgUploadPath are changed appropriately.
  68    * skins/*/: Subdirectories of skins/ contain CSS and JavaScript files that
  69    must be accessible to web browsers.  The PHP files and Skin.sample in skins/
  70    don't need to be accessible.  This could be somewhere else if
  71    $wgStyleDirectory and $wgStylePath are changed appropriately.
  72    * extensions/: Many extensions include CSS and JavaScript files in their
  73    extensions directory, and will break if they aren't web-accessible.  Some
  74    extensions might theoretically provide additional entry points as well, at
  75    least in principle.
  76  
  77  But all files should keep their position relative to the web-visible
  78  installation directory no matter what.  If you must move includes/ somewhere in
  79  /usr/share, provide a symlink from /var/www/w.  If you don't, you *will* break
  80  something.  You have been warned.
  81  
  82  == Configuration ==
  83  
  84  MediaWiki is configured using LocalSettings.php.  This is a PHP file that's
  85  generated when the user visits mw-config/index.php to install the software, and
  86  which the user can edit by hand thereafter.  It's just a plain old PHP file,
  87  and can contain any PHP statements.  It usually sets global variables that are
  88  used for configuration, and includes files used by any extensions.
  89  
  90  Distributors can easily add extra statements to the autogenerated
  91  LocalSettings.php by changing mw-config/overrides.php (see that file for details
  92  and examples).
  93  
  94  There's a new maintenance/install.php script which could be used for performing
  95  an install through the command line.
  96  
  97  Some configuration options that distributors might be in a position to set
  98  intelligently:
  99  
 100    * $wgEmergencyContact: An e-mail address that can be used to contact the wiki
 101    administrator.  By default, "wikiadmin@ServerName".
 102    * $wgPasswordSender: The e-mail address to use when sending password e-mails.
 103    By default, "MediaWiki Mail <apache@ServerName>".
 104      (with ServerName guessed from the http request)
 105    * $wgSMTP: Can be configured to use SMTP for mail sending instead of PHP
 106    mail().
 107  
 108  == Updates ==
 109  
 110  The correct way for updating a wiki is to update the files and then run from 
 111  command line the maintenance/update.php script (with appropriate parameters if
 112  files were moved). It will perform all the needed steps to update the database 
 113  schema and contents to the version from whatever old one it has.
 114  Any package manager which replaces the files but doesn't update the db is leaving
 115  an inconsistent wiki that may produce blank pages (php errors) when new features 
 116  using the changed schema would be used.
 117  
 118  Since MediaWiki 1.17 it is possible to upgrade using the installer by providing 
 119  an arbitrary secret value stored as $wgUpgradeKey in LocalSettings (older versions 
 120  needed to rename LocalSettings.php in order to upgrade using the installer).
 121  
 122  == Documentation ==
 123  
 124  MediaWiki's official documentation is split between two places: the source
 125  code, and <https://www.mediawiki.org/>.  The source code documentation is written
 126  exclusively by developers, and so is likely to be reliable (at worst,
 127  outdated).  However, it can be pretty sparse.  mediawiki.org documentation is
 128  often much more thorough, but it's maintained by a wiki that's open to
 129  anonymous edits, so its quality is sometimes sketchy -- don't assume that
 130  anything there is officially endorsed!
 131  
 132  == Upstream ==
 133  
 134  MediaWiki is a project hosted and led by the Wikimedia Foundation, the
 135  not-for-profit charity that operates Wikipedia.  Wikimedia employs the lead
 136  developer and several other paid developers, but commit access is given out
 137  liberally and there are multiple very active volunteer developers as well.  A
 138  list of developers can be found at <https://www.mediawiki.org/wiki/Developers>.
 139  
 140  MediaWiki's bug tracker is at <https://bugzilla.wikimedia.org>.  However, most
 141  developers follow the bug tracker little or not at all.  The best place to
 142  post if you want to get developers' attention is the wikitech-l mailing list
 143  <https://lists.wikimedia.org/mailman/listinfo/wikitech-l>.  Posts to wikitech-l
 144  will inevitably be read by multiple experienced MediaWiki developers.  There's
 145  also an active IRC chat at <irc://irc.freenode.net/mediawiki>, where there are
 146  usually several developers at reasonably busy times of day.
 147  
 148  Unfortunately, we don't have a very good system for patch review.  Patches
 149  should be submitted on Bugzilla (as unified diffs produced with "svn diff"
 150  against the latest trunk revision), but many patches languish without review
 151  until they bitrot into uselessness.  You might want to get a developer to
 152  commit to reviewing your patch before you put too much effort into it.
 153  Reasonably straightforward patches shouldn't be too hard to get accepted if
 154  there's an interested developer, however -- posting to Bugzilla and then
 155  dropping a note on wikitech-l if nobody responds is a good tactic.
 156  
 157  All redistributors of MediaWiki should be subscribed to mediawiki-announce
 158  <https://lists.wikimedia.org/mailman/listinfo/mediawiki-announce>.  It's
 159  extremely low-traffic, with an average of less than one post per month.  All
 160  new releases are announced here, including critical security updates.
 161  
 162  == Useful software to install ==
 163  
 164  There are several other pieces of software that MediaWiki can make good use of.
 165  Distributors might choose to install these automatically with MediaWiki and
 166  perhaps configure it to use them (see Configuration section of this document):
 167  
 168    * APC (Alternative PHP Cache), XCache, or similar: Will greatly speed up the
 169    execution of MediaWiki, and all other PHP applications, at some cost in
 170    memory usage.  Will be used automatically for the most part.
 171    * clamav: Can be used for virus scanning of uploaded files.  Enable with
 172    "$wgAntivirus = 'clamav';".
 173    * DjVuLibre: Allows processing of DjVu files.  To enable this, set
 174    "$wgDjvuDump = 'djvudump'; $wgDjvuRenderer = 'ddjvu'; $wgDjvuTxt = 'djvutxt';".
 175    * HTML Tidy: Fixes errors in HTML at runtime.  Can be enabled with 
 176      "$wgUseTidy = true;".
 177    * ImageMagick: For resizing images.  "$wgUseImageMagick = true;" will enable
 178    it.  PHP's GD can also be used, but ImageMagick is preferable.
 179    * Squid: Can provide a drastic speedup and a major cut in resource
 180    consumption, but enabling it may interfere with other applications.  It might
 181    be suitable for a separate mediawiki-squid package.  For setup details, see:
 182    <https://www.mediawiki.org/wiki/Manual:Squid_caching>
 183    * rsvg or other SVG rasterizer: ImageMagick can be used for SVG support, but
 184    is not ideal.  Wikipedia (as of the time of this writing) uses rsvg.  To
 185    enable, set "$wgSVGConverter = 'rsvg';" (or other as appropriate).
 186    * texvc: Included with MediaWiki.  Instructions for compiling and
 187    installing it are in the math/ directory.
 188  
 189  MediaWiki uses some standard GNU utilities as well, such as diff and diff3.  If
 190  these are present in /usr/bin or some other reasonable location, they will be
 191  configured automatically on install.
 192  
 193  MediaWiki also has a "job queue" that handles background processing.  Because
 194  shared hosts often don't provide access to cron, the job queue is run on every
 195  page view by default.  This means the background tasks aren't really done in
 196  the background.  Busy wikis can set $wgJobRunRate to 0 and run
 197  maintenance/runJobs.php periodically out of cron.  Distributors probably
 198  shouldn't set this up as a default, however, since the extra cron job is
 199  unnecessary overhead for a little-used wiki.
 200  
 201  == Web server configuration ==
 202  
 203  MediaWiki includes several .htaccess files to restrict access to some
 204  directories.  If the web server is not configured to support these files, and
 205  the relevant directories haven't been moved someplace inaccessible anyway (e.g.
 206  symlinked in /usr/share with the web server configured to not follow symlinks),
 207  then it might be useful to deny web access to those directories in the web
 208  server's configuration.