docs/distributors.txt

   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.