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. These are the entry points for normal usage. This list may be
  63   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 change the installer behavior, including LocalSettings
  91 generated, by placing their overrides into mw-config/overrides directory. Doing
  92 that is highly preferred to modifying MediaWiki code directly. See
  93 mw-config/overrides/README for more details and examples.
  94
  95 There's a new maintenance/install.php script which could be used for performing
  96 an install through the command line.
  97
  98 Some configuration options that distributors might be in a position to set
  99 intelligently:
 100
 101   * $wgEmergencyContact: An e-mail address that can be used to contact the wiki
 102   administrator. By default, "wikiadmin@ServerName".
 103   * $wgPasswordSender: The e-mail address to use when sending password e-mails.
 104   By default, "MediaWiki Mail <apache@ServerName>".
 105         (with ServerName guessed from the http request)
 106   * $wgSMTP: Can be configured to use SMTP for mail sending instead of PHP
 107   mail().
 108
 109 == Updates ==
 110
 111 The correct way for updating a wiki is to update the files and then run from
 112 command line the maintenance/update.php script (with appropriate parameters if
 113 files were moved). It will perform all the needed steps to update the database
 114 schema and contents to the version from whatever old one it has.
 115 Any package manager which replaces the files but doesn't update the db is leaving
 116 an inconsistent wiki that may produce blank pages (php errors) when new features
 117 using the changed schema would be used.
 118
 119 Since MediaWiki 1.17 it is possible to upgrade using the web installer by providing
 120 an arbitrary secret value stored as $wgUpgradeKey in LocalSettings (older versions
 121 needed to rename LocalSettings.php in order to upgrade using the installer).
 122
 123 == Documentation ==
 124
 125 MediaWiki's official documentation is split between two places: the source
 126 code, and <https://www.mediawiki.org/>. The source code documentation is written
 127 exclusively by developers, and so is likely to be reliable (at worst,
 128 outdated). However, it can be pretty sparse. mediawiki.org documentation is
 129 often much more thorough, but it's maintained by a wiki that's open to
 130 anonymous edits, so its quality is sometimes sketchy -- don't assume that
 131 anything there is officially endorsed!
 132
 133 == Upstream ==
 134
 135 MediaWiki is a project hosted and led by the Wikimedia Foundation, the
 136 not-for-profit charity that operates Wikipedia. Wikimedia employs the lead
 137 developer and several other paid developers, but commit access is given out
 138 liberally and there are multiple very active volunteer developers as well. A
 139 list of developers can be found at <https://www.mediawiki.org/wiki/Developers>.
 140
 141 MediaWiki's bug tracker is at <https://phabricator.wikimedia.org>. However, you
 142 might find that the best place to post if you want to get developers' attention
 143 is the wikitech-l mailing list
 144 <https://lists.wikimedia.org/mailman/listinfo/wikitech-l>. Posts to wikitech-l
 145 will inevitably be read by multiple experienced MediaWiki developers. There's
 146 also an active IRC chat at <irc://irc.freenode.net/mediawiki>, where there are
 147 usually several developers at reasonably busy times of day.
 148
 149 Our Git repositories are hosted at <https://gerrit.wikimedia.org>, see
 150 <https://www.mediawiki.org/wiki/Gerrit> for more information. Patches should
 151 be submitted there. If you know which developers are best suited to review your
 152 patch, add them to it, otherwise ask on IRC to get better review time.
 153
 154 All redistributors of MediaWiki should be subscribed to mediawiki-announce
 155 <https://lists.wikimedia.org/mailman/listinfo/mediawiki-announce>. It's
 156 extremely low-traffic, with an average of less than one post per month. All
 157 new releases are announced here, including critical security updates.
 158
 159 == Useful software to install ==
 160
 161 There are several other pieces of software that MediaWiki can make good use of.
 162 Distributors might choose to install these automatically with MediaWiki and
 163 perhaps configure it to use them (see Configuration section of this document):
 164
 165   * APC (Alternative PHP Cache) or similar: Will greatly speed up the
 166   execution of MediaWiki, and all other PHP applications, at some cost in
 167   memory usage. Will be used automatically for the most part.
 168   * clamav: Can be used for virus scanning of uploaded files. Enable with
 169   "$wgAntivirus = 'clamav';".
 170   * DjVuLibre: Allows processing of DjVu files. To enable this, set
 171   "$wgDjvuDump = 'djvudump'; $wgDjvuRenderer = 'ddjvu'; $wgDjvuTxt = 'djvutxt';".
 172   * HTML Tidy: Fixes errors in HTML at runtime. Can be enabled with
 173         "$wgUseTidy = true;".
 174   * ImageMagick: For resizing images. "$wgUseImageMagick = true;" will enable
 175   it. PHP's GD can also be used, but ImageMagick is preferable.
 176   * HTTP cache such as Varnish or Squid: can provide a drastic speedup and a
 177   major cut in resource consumption, but enabling it may interfere with other
 178   applications. It might be suitable for a separate package. For setup details, see:
 179   - <https://www.mediawiki.org/wiki/Manual:Varnish_caching>
 180   - <https://www.mediawiki.org/wiki/Manual:Squid_caching>
 181   * rsvg or other SVG rasterizer: ImageMagick can be used for SVG support, but
 182   is not ideal. Wikipedia (as of the time of this writing) uses rsvg. To
 183   enable, set "$wgSVGConverter = 'rsvg';" (or other as appropriate).
 184
 185 MediaWiki uses some standard GNU utilities as well, such as diff and diff3. If
 186 these are present in /usr/bin or some other reasonable location, they will be
 187 configured automatically on install.
 188
 189 MediaWiki also has a "job queue" that handles background processing. Because
 190 shared hosts often don't provide access to cron, the job queue is run on every
 191 page view by default. This means the background tasks aren't really done in
 192 the background. Busy wikis can set $wgJobRunRate to 0 and run
 193 maintenance/runJobs.php periodically out of cron. Distributors probably
 194 shouldn't set this up as a default, however, since the extra cron job is
 195 unnecessary overhead for a little-used wiki.
 196
 197 == Web server configuration ==
 198
 199 MediaWiki includes several .htaccess files to restrict access to some
 200 directories. If the web server is not configured to support these files, and
 201 the relevant directories haven't been moved someplace inaccessible anyway (e.g.
 202 symlinked in /usr/share with the web server configured to not follow symlinks),
 203 then it might be useful to deny web access to those directories in the web
 204 server's configuration.