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    <title>Frequently Asked Questions</title>
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  <div id=content>
<h1>Frequently Asked Questions</h1>
<h2 id="other-servers">I'm not running Apache or Nginx, do you support my
http server?</h2>

<p>
While we only support Apache and Nginx, there are community developed ports to
several other webservers:
</p>
<ul>
<li><a
href="https://cwiki.apache.org/confluence/display/TS/ats_speed">Apache
Traffic Server</a></li>
<li><a href="http://www.iispeed.com/"
>Internet Information Services (IIS)</a></li>
<li><a
href="http://open.litespeedtech.com/mediawiki/index.php/Help:Modules:PageSpeed"
>OpenLiteSpeed</a></li>
</ul>
<p>
If you run a webserver that doesn't have a port, one option would be to set up
some other server running PageSpeed as a reverse proxy in front of it.  If
you're not sure which to use we recommend using PageSpeed on nginx, but any of
these servers should work well as an optimizing reverse proxy.
</p>
<p>
(And, of course, if you're interested in porting PageSpeed to a new server, that
would be awesome, and anyone porting should feel free to send us lots of
detailed technical questions!)
</p>

<h2 id="when-support">When will you support my favorite OS or protocol?</h2>

<p>
While we have no dates to announce for upcoming releases, we definitely want to
know what you think we should be working
on. Please <a href="https://github.com/apache/incubator-pagespeed-mod/issues">search
our issues</a> for your feature. If you don't find
it, <a href="https://github.com/apache/incubator-pagespeed-mod/issues/new">open a new
issue</a> and tag it "Type-Enhancement". To get updates on an issue, click the
"star" icon for it.  This also lets us know how many people are interested in
the issue.  If your issue is Nginx-specific, consider posting on
the <a href="https://github.com/apache/incubator-pagespeed-ngx/issues">ngx_pagespeed
bug tracker</a>.
</p>

<h2 id="suse">Do you support SUSE?</h2>
<p>
We support SUSE on Apache and Nginx when <a href="build_from_source">building
from source</a>.  For Apache, Robert Munteanu (robert.munteanu@gmail.com) has
set up a repository which publishes OpenSUSE RPMs for mod_pagespeed. The
repository is
hosted <a href="http://software.opensuse.org/package/apache2-mod_pagespeed">on
OpenSUSE's build service instance</a>.  The builds have seen some testing on one
of Robert's servers (OpenSUSE 12.1/x86_64) but he'd appreciate anyone else
testing it.
</p>
<p>
To enable the module, install it, add <code>deflate pagespeed</code> to your
list of Apache modules in <code>/etc/sysconfig/apache2</code> and restart
Apache.
</p>
<p>
Please note that the module is linked dynamically with the current system
libraries and as such will bring in more dependencies than the 'stock' Fedora or
CentOS RPM.
</p>

<h2 id="not-rewriting">Why isn't PageSpeed rewriting any of my pages?</h2>
<p>
Check the HTTP response headers from your HTML page:
</p>
<pre class="prettyprint lang-bsh">
  curl -D- http://example.com | less
</pre>
<p>
You should get something like:
</p>
<dl>
  <dt>Apache:<dd>
<pre>
Date: Fri, 30 Sep 2016 15:36:57 GMT
Server: Apache/2.4.7 (Ubuntu)
...
X-Mod-Pagespeed: 1.11.33.4-0
...
</pre>
  <dt>Nginx:<dd>
<pre>
Date: Fri, 30 Sep 2016 15:37:24 GMT
Server: nginx/1.11.4
...
X-Page-Speed: 1.11.33.4-0
</pre>
</dl>
<p>
If you don't see an <code>X-Mod-Pagespeed</code> header (Apache)
or <code>X-Page-Speed</code> header (Nginx), this means that your webserver
isn't letting PageSpeed run.  This could be because it isn't actually installed,
you don't have it turned on in the configuration file, or many other reasons.
In Apache the problem might be that you have multiple
<code>SetOutputFilter</code> directives: only one of those will win. See the
Apache <a
href="http://httpd.apache.org/docs/current/mod/core.html#SetOutputFilter"
>SetOutputFilter documentation</a>.
</p>
<p>
If you do see the header, but it doesn't look like PageSpeed is making any
changes to your page, its possible that none of the active filters are finding
anything to rewrite.  Try comparing your page with PageSpeed off and with
the <a href="filter-whitespace-collapse">collapse_whitespace</a> filter enabled:
</p>
<pre class="prettyprint">
  curl -D- 'http://example.com?ModPagespeed=off' | less
  curl -D- 'http://example.com?ModPagespeed=on&ModPagespeedFilters=collapse_whitespace' | less
</pre>
<p>
If you see a change when run with <code>collapse_whitespace</code> on, that
means PageSpeed is running but the filters you have selected aren't
optimizing anything.  There are several reasons that could happen:
</p>
<ul>
  <li>The filters you have enabled aren't aggressive enough.</li>
  <li>Your resources (images, css, javascript) aren't cacheable.  If
      PageSpeed sees <code>cache-control</code> headers such
      as <code>nocache</code> or <code>private</code> it will not rewrite the
      resources.</li>
  <li>CSS, JavaScript, and image files served from a distinct domain from the
      HTML must have the resource domain authorized. See
      <a href="domains">Domains</a>.</li>
  <li>Your CSS has new CSS3 syntax or other constructions we don't support.
      See <a href="http://github.com/apache/incubator-pagespeed-mod/issues/108"
      >issue 108</a>.
      The <a href="filter-css-rewrite#configuration"
      >fallback_rewrite_css_urls</a> filter may be able to help. You can also
      use the <a href="build_from_source#debug-css">standalone CSS parser</a> to
      help debug these issues.</li>
  <li>Your resources are served over HTTPS.   HTTPS resources can currently only
      be rewritten if they are origin-mapped or loaded from directly from the
      file-system. See <a href="https_support">HTTPS Support</a>.</li>
</ul>

<h2 id="missing-dependency">Why am I getting "Error: Missing Dependency: httpd &gt; = 2.2" even though I have Apache 2.2.? installed?</h2>
<p>
  You are probably trying to install mod_pagespeed using yum or apt-get
  (the .rpm or .deb binaries), but you installed Apache using a different
  method (cPanel, Wordpress, etc.). This will not work because mod_pagespeed
  binaries depend upon Apache being installed using yum or apt-get.
</p>
<p>
  Instead you must either
  <a href="build_mod_pagespeed_from_source">
    build from mod_pagespeed from source
  </a>
  or <a href="http://www.google.com/">search</a> for mod_pagespeed + your
  platform to see if someone has documented an install process for that
  platform. For example,
  <a href="#cpanel-install">cPanel based installation</a>.
</p>

<h2 id="cpanel-install">I'm using cPanel on my server, how do I install mod_pagespeed?</h2>
<p>
cPanel installs Apache httpd server from source via the built-in EasyApache setup
and build process. In order to enable mod_pagespeed on your server, download
and install the <a href="https://github.com/apache/incubator-pagespeed-cpanel">mod_pagespeed module
 for cPanel WHM</a> - once the module is installed, you can select "mod_pagespeed" as
one of the modules during the regular EasyApache build (via the online tool, or from
the command line). Do not install mod_pagespeed from .deb. or .rpm packages - cPanel
requires that you use the EasyApache build process.
</p>

<h2 id="wordpress-blank">I'm using WordPress and my pages are blank. Why?</h2>
<p>
Disable compression in the WordPress plugin, so that mod_pagespeed will process
uncompressed HTML. mod_pagespeed ensures that its output will be compressed by
enabling <a href="http://httpd.apache.org/docs/current/mod/mod_deflate.html"
>mod_deflate</a>.
</p>

<h2 id="broken">PageSpeed broke my site; what do I do?</h2>
<p>
First of all, sorry about that. We put a lot of work into validating our
rewriters against a large corpus of websites and we disable filters that cause
problems as soon as we can, but sometimes things slip through.
</p>
<p>
Second, please upgrade to the latest version; we are continually working on
bug-fixes and turning off filters that break pages.
</p>
If it's still breaking your site, please post a bug
(<a href="https://github.com/apache/incubator-pagespeed-mod/issues/new">Apache</a>,
 <a href="https://github.com/apache/incubator-pagespeed-ngx/issues/new">Nginx</a>). If
you can, including the following information will make it much easier to
diagnose:
<ol>
  <li>Try appending <code>?ModPagespeed=off</code> to the URL. This de-activates
      PageSpeed. If the site is still broken, it is not a rewrite
      or HTML parsing problem. It might be a configuration clash, please ask us
      on our <a href="mailing-lists#discussion">discussion group</a>.</li>
  <li>If that fixed the site, try
      appending <code>?ModPagespeed=on&ModPagespeedFilters=</code> to the
      URL. This turns on PageSpeed, but no filters. If the site is broken
      now, it is an HTML parsing
      problem. Please <a href="mailing-lists#discussion">let us know</a>.</li>
  <li>If the site still worked, try
      appending <code>?ModPagespeed=on&ModPagespeedFilters=foo</code> for
      various filters "foo". For example try:
      <pre class="prettyprint lang-bsh">
http://www.modpagespeed.com/?ModPagespeed=on&ModPagespeedFilters=extend_cache
http://www.modpagespeed.com/?ModPagespeed=on&ModPagespeedFilters=combine_css
http://www.modpagespeed.com/?ModPagespeed=on&ModPagespeedFilters=inline_css
http://www.modpagespeed.com/?ModPagespeed=on&ModPagespeedFilters=inline_javascript
http://www.modpagespeed.com/?ModPagespeed=on&ModPagespeedFilters=insert_image_dimensions
http://www.modpagespeed.com/?ModPagespeed=on&ModPagespeedFilters=rewrite_images
http://www.modpagespeed.com/?ModPagespeed=on&ModPagespeedFilters=rewrite_css
http://www.modpagespeed.com/?ModPagespeed=on&ModPagespeedFilters=rewrite_javascript</pre>
      You may have to reload them a few times over several seconds to make sure
      they have had time to load sub-resources into cache and rewrite them. If
      one of these breaks your site, you now know which filter is at
      fault. Please <a href="mailing-lists#discussion">let us know</a>. You can
      disable that filter by adding a line to your <code>pagespeed.conf</code>
      file:
<dl>
  <dt>Apache:<dd><pre class="prettyprint"
     >ModPagespeedDisableFilters foo</pre>
  <dt>Nginx:<dd><pre class="prettyprint"
     >pagespeed DisableFilters foo;</pre>
</dl>
  </li>
</ol>

<h2 id="mod_rewrite">I am getting 404s for rewritten resources
  (like example.png.pagespeed.ic.LxXAhtOwRv.png) or for the
  mod_pagespeed_admin console</h2>
<p>
  The most common reason that the rewritten resources 404 is because of
  mod_rewrite <code>RewriteCond</code> rules. For example:
</p>
<pre class="prettyprint">
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^ /404 [L,R=301]</pre>
<p>
  This rule causes 404 for all requests which don't exist on the filesystem,
  including mod_pagespeed rewritten resources and the mod_pagespeed admin
  console.
</p>
<p>
  In order to fix this you must add an exception for mod_pagespeed URLs:
</p>
<pre class="prettyprint">
  RewriteCond %{REQUEST_URI} !pagespeed</pre>
<p>
  This will allow rewritten resources, the admin console and static resources
  necessary for some filters.
</p>

<h2 id="ignores-changes">PageSpeed does not pick up changes when I edit CSS
or JavaScript files</h2>
<p>
There are two distinct cache-times at play when you use PageSpeed:
<ol>
  <li>The origin TTL which PageSpeed uses to refresh its internal
      server-side cache.</li>
  <li>The TTL with which PageSpeed serves rewritten resources to
      browsers.</li>
</ol>
When PageSpeed first reads your resource file, it uses the origin TTL to figure
out how often to re-examine the origin CSS file. Assume your origin TTL is 1
day. Once PageSpeed has that file in cache, it will not go back &amp; re-check
that file for a day. Changing the TTL after PageSpeed has put the resource in
its cache will not help because PageSpeed is not going to reload the resource
until the one in its cache expires, or you <a href="system#flush_cache">clear
its cache</a>.
</p>
<p>
We recommend an origin TTL of 10 minutes, which provides reasonable
responsiveness when you update a file. If you try to make it much smaller, then
your server will need to refresh it more frequently. This adds server load and
reduces optimization.
</p>
<p>
To see changes to your files more quickly while
developing, <a href="system#flush_cache">flush the cache</a> on your server(s).
</p>
<p>
If your environment allows you to
enable <a href="domains#ModPagespeedLoadFromFile">LoadFromFile</a>,
you can get the best of both worlds because PageSpeed can eliminate its
internal server-side cache.
</p>
<h2 id="tiny-mce-errors">Why is PageSpeed giving me errors in jquery or
js_tinyMCE?</h2>
<p>
Some JavaScript is introspective, being sensitive to its own name or the path
it's loaded from.  While PageSpeed has an internal list
(<a href="https://github.com/apache/incubator-pagespeed-mod/blob/master/net/instaweb/rewriter/rewrite_options.cc">DisallowTroublesomeResources</a>)
hardcoded with filenames of JavaScript libraries that are known to be
problematic, and <a href="restricting_urls#aris">inspects the source of
others</a> looking for dangerous constructs, it doesn't always correctly
determine whether it is safe to rewrite a given file.  If you have a file that
is giving JavaScript errors, you can tell PageSpeed to leave it alone with
<a href="restricting_urls">Disallow</a>.
</p>
<h2 id="name-resolution-failure">What's with all these "Serf" errors in my logs?
Error status=670003 (Temporary failure in name resolution)</h2>
<p>
This can happen when the DNS cannot be accessed accurately from the server. Thus
sub-resources cannot be fetched and rewritten correctly.
</p>
<p>
To test that this is the case, <code>ssh</code> into your machine and <code>wget</code> a URL:
</p>
<pre class="prettyprint lang-bsh">
  $ ssh YOUR_SITE
  $ wget http://YOUR_SITE/
</pre>
<p>
If this fails, then DNS is not accessible or there is some other networking
issue stopping you from accessing your host from itself.
</p>
<p>
One solution is to use <a href="domains#mapping_origin">origin-mapping</a> to
indicate the host from which the resources should be fetched:
</p>
<dl>
  <dt>Apache:<dd><pre class="prettyprint"
     >ModPagespeedMapOriginDomain localhost www.example.com</pre>
  <dt>Nginx:<dd><pre class="prettyprint"
     >pagespeed MapOriginDomain localhost www.example.com;</pre>
</dl>
<p>
This bypasses DNS lookup by telling PageSpeed to get all resources for
domain <code>www.example.com</code> from <code>localhost</code>.
</p>
<p>
This can also be used to improve the performance of PageSpeed when it is
sitting behind a load balancer. It may be preferable to use localhost to load
the resources rather than going out to the load-balancer and back.
</p>
<h2 id="tmpfs">Can I move PageSpeed's file-based cache into RAM?</h2>
<p>
Why yes, you can. PageSpeed uses the file system for its cache
implementation. There is no requirement that this be a physical disk. Disk
pressure will be reduced and performance may be improved by using a memory-based
file system.
</p>
<p>
Put this in <code>/etc/fstab</code>, with the uid and guid set to the appropiate
user and group of your webserver, and set path to your needs. Feel free to
change the size; here it is 256Mb:
<pre class="prettyprint lang-bsh">
  tmpfs /path/to/pagespeed_cache tmpfs size=256m,mode=0775,uid=httpd,gid=httpd 0 0
</pre>
<p>
Save it, and after that mount the tmpfs:
</p>
<pre class="prettyprint lang-bsh">
  mount /path/to/pagespeed_cache
</pre>
<h2 id="configure-make">Why don't you allow source-installs in Apache via
./configure && make?</h2>
<p>
mod_pagespeed is dependent on several other packages that
use <code>gclient</code>.  For us to switch away from this build methodology
we'd have to either:
</p>
<ul>
  <li>rewrite the functionality we get for free from other packages,
      <b>or</b></li>
  <li>get these packages to switch
      methodologies <b>and</b> document for people installing from source that
      they must <code>configure</code> and <code>make</code> about 10 other
      packages before they could compile ours.</li>
</ul>
<p>
To do either of those would cost us a lot of development time that we'd prefer
to spend making PageSpeed better.  The benefit of <code>gclient</code>,
besides the above, is that it lets us control explicitly which library versions
we link in, out of a large number of direct and transitive dependencies, helping
us create a consistent experience for our source-code builds. If we had to ask
our source-code installers to <code>configure</code> and <code>make</code>
multiple dependent libraries there would likely be a lot of
version-incompatibilities.
</p>
<p>
We do support <code>./configure && make</code> in Nginx, but that only works
because we package up a binary distribution of the PageSpeed Optimization
Library and a "<a href="build_ngx_pagespeed_from_source">source</a>"
installation only builds the ngx_pagespeed-specific files from source.  When you
want
to <a href="https://github.com/apache/incubator-pagespeed-ngx/wiki/Building-PSOL-From-Source">build
PSOL from source along with ngx_pagespeed</a> you still need to
use <code>gclient</code>.
</p>
<h2 id="tracking-image">Why is my Google Analytics data being inflated by
"Serf"?</h2>
<p>
If you track page views with a tracking image, you will need to explicitly tell
PageSpeed not to try to fetch that image. For example if your tracking image
were:
</p>
<pre class="prettyprint">
  &lt;img src="/ga.php?utmac=..."&gt;
</pre>
<p>
you would add:
</p>
<dl>
  <dt>Apache:<dd><pre class="prettyprint"
     >ModPagespeedDisallow "*/ga.php*"</pre>
  <dt>Nginx:<dd><pre class="prettyprint"
     >pagespeed Disallow "*/ga.php*";</pre>
</dl>
<p>
to your configuration file.
</p>
<h2 id="mod_php">mod_pagespeed does not rewrite pages produced from mod_php</h2>
<p>
mod_pagespeed only rewrites pages specifically marked as <code>Content-Type:
text/html</code> (and a few other HTML types). If you dynamically generate your
pages from mod_php, PHP needs to set this header correctly.
</p>
<p>
One way to do this is to use the PHP's <a href="http://php.net/manual/en/function.header.php">header function</a>:
</p>
<pre class="prettyprint">
  &lt;?php
  header('Content-Type: text/html')
  ?&gt;
</pre>
<p>
This code goes at the top of your php file.
</p>
<h2 id="meta_tags_and_xhtml">PageSpeed causes my page to display an <code>XML
Parsing Error</code> message</h2>
<p>
This usually happens when using a content management or generation system
(we've seen it with Munin and Magento for example). The full error message
looks something like:
</p>
<pre class="prettyprint">
  XML Parsing Error: mismatched tag. Expected: &lt;/li&gt;.
  Location: http://www.example.com/
  Line Number 123, Column 4: &lt;/ul&gt;
</pre>
<p>
This happens when the generated content has a <code>meta</code> tag that
identifies the content as XHTML but the content has markup that is not valid
XHTML, <em>and</em> you have configured your webserver to set the content type
to HTML, so the browser parses it as HTML and doesn't detect the invalid XHTML
errors.
</p>
<p>
However, when <code>convert_meta_tags</code> is enabled (and it's a core filter
so is on by default), PageSpeed inserts a content header into the response
with the value in the <code>meta</code> tag, namely XHTML
(<code>application/xhtml+xml</code> to be precise), resulting in the browser
displaying the error message because it is now parsing the page as XHTML and
it rejects the invalid content.
</p>
<p>
There are three solutions, in descending order of preference:
<ul>
<li>If the content is XHTML, write XHTML and validate it with an XHTML
  validator.</li>
<li>If the content is not XHTML, remove the <code>meta</code> tag that claims
  it is.</li>
<li>If the content is not XHTML but you can't remove the <code>meta</code> tag,
  say because your CMS doesn't let you, disable the
  <code>convert_meta_tags</code> filter in your <code>pagespeed.conf</code>:
</p>
<dl>
  <dt>Apache:<dd><pre class="prettyprint"
     >ModPagespeedDisableFilters convert_meta_tags</pre>
  <dt>Nginx:<dd><pre class="prettyprint"
     >pagespeed DisableFilters convert_meta_tags;</pre>
</dl>
</li>
</ul>
<h2 id="selinux_permissions">Why do I get <em>Permission denied</em> errors
  in my log file on CentOS, RHEL, or any system using SELinux?</h2>
<p>
The symptom is many error messages in the webserver log file of the form (split
across multiple lines here for readability):
</p>
<pre class="prettyprint">
  [Mon Jan 01 02:03:04 2001] [error] [mod_pagespeed 1.0.22.7-2005 @1234]
    /path/to/pagespeed_cache/randomgibberish.lock:0:
      creating dir (code=13 Permission denied)
</pre>
<p>
These are because SELinux by default restricts permissions of daemons for
extra security, so you need to grant permission for the <code>httpd</code>
or daemon to write to the cache directory:
</p>
<pre class="prettyprint">
  chcon -R -t httpd_sys_content_t /path/to/pagespeed_cache
</pre>
This is for Apache; we're not sure what you need to do for Nginx.

<h2 id="loopback_fetches">My logs contain messages about missing
files requested from 224.0.0.0 and resources are not optimized, what's wrong?</h2>
<p>

For <a href="CVE-2012-4001">security reasons</a>, PageSpeed will only fetch
from host names it is explicitly told about via its domain configuration
directives and from 127.0.0.1, the loopback interface of the server it's running
on. Many Apache configuration management tools, however, will configure virtual
hosts to only listen on the external IP, which causes those fetches to fail.
<p>
If you are affected, the following options may be appropriate:
<ul>
 <li>Unless you have a reason not to, have your virtual hosts listen on all
    interfaces: change the directives of the form
     <code>&lt;VirtualHost 198.51.100.1:80&gt;</code> to the form
     <code>&lt;VirtualHost *:80&gt;</code>
 </li>
 <li>For every virtual host, list its domain name(s) with the
     <code>ModPagespeedDomain</code> directive inside its own
     <code>&lt;VirtualHost&gt;</code> block. For example:
     <pre class="prettyprint">
&lt;VirtualHost 198.51.100.1:80&gt;
ServerName www.example.com
ModPagespeedDomain www.example.com
</pre>
  </li>
  <li>For every virtual host, provide a <a href="domains#mapping_origin">
  <code>ModPagespeedMapOriginDomain</code></a> directive giving where to load
  its resources, for example:
     <pre class="prettyprint">
&lt;VirtualHost 198.51.100.1:80&gt;
ServerName www.example.com
ModPagespeedMapOriginDomain 198.51.100.1 www.example.com
</pre>
  </li>
  <li>If you have <a href="configuration#virtual-hosts">
  <code>ModPagespeedInheritVHostConfig on</code></a>, you can also provide the
  origin mapping globally, which may be useful in combination with wildcards,
  for example:
    <pre class="prettyprint">
ModPagespeedMapOriginDomain loadbalancer.example.com *.example.com
</pre>

  <p class="warning"><b>Warning:</b> You do not generally want to use
    <code>Domain</code> globally as doing so will tell PageSpeed
    that you consider all of these domains as mutually trusting.</p>
 </li>
 <li>If you are running a proxy or for some other reason cannot easily
     enumerate all virtual hosts, it is possible to disable this behavior,
     after taking some precautions. Please see
     <a href="domains#fetch_servers">fetch server restrictions</a> for
     more information.
  </li>
</ul>

<h2 id="beacons">Why are rewritten pages sending POSTs back to my server?</h2>
<p>
Certain filters need to determine things about the page: in particular, the
<code><a href="filter-lazyload-images">lazyload_images</a></code>,
<code><a href="filter-inline-preview-images">inline_preview_images</a></code>,
and <code><a href="reference-image-optimize#inline_images">inline_images</a>
</code> filters need to determine which images are above the fold, and the
<code><a href="filter-prioritize-critical-css">prioritize_critical_css</a>
</code>filter needs to determine the CSS actually used by the page.
<p>
</p>To do this, the filters inject JavaScript into the rewritten HTML that
analyzes the page in the browser and sends data back to mod_pagespeed using a
POST method. The default target is <code>/mod_pagespeed_beacon</code> but that
can be changed using the <code>
<a href="filter-instrumentation-add#beacon_url">ModPagespeedBeaconUrl</a>
</code> directive.
</p>

<h2 id="control_beacons">How do I enable or disable beacon POSTs being sent back
to my server?</h2>
<p>
Filters that use the beacon automatically inject JavaScript to send the POST
back to the server, and the POST handler is always enabled in mod_pagespeed,
so there's nothing to do to enable beaconing.
</p>
<p>
To disable the use of beacons by the image rewriting filters use the <code>
<a href="config_filters#beacons">ModPagespeedCriticalImagesBeaconEnabled</a>
</code> directive. If you disable image beacons but enable filters that use
them, the filters will work but not as well as when beacons are enabled.
<p>
To disable the POST handler for all filters there are two options: either
disable all the filters that use it, or use a
<code>&lt;Location&gt;</code> directive to block it. Filters are disabled using
<a href="config_filters#enabling">ModPagespeedDisableFilters</a>. An example
<code>&lt;Location&gt;</code> directive to block all beacon POST handling that
can be added to your <code>pagespeed.conf</code> file is:
<pre class="prettyprint" id="disable_handler">
  &lt;Location /mod_pagespeed_beacon&gt;
    Order allow,deny
  &lt;/Location&gt;
</pre>
<p>
If you block POSTs but enable filters that use beacons, depending on the filter
it will either have limited functionality or have no useful effect, but in all
cases pointless processing will occur in both the server and the browser, so
you should disable and forbid these filters if you block POSTs.
</p>
<p class="note">
<strong>Note:</strong>Even if you disable all filters that use beacons someone
could use tools like <code>wget</code> or <code>curl</code> to send POSTs to
your server. These will have no effect but they will require processing. If you
want to completely disable POST handling use a <code>&lt;Location&gt;</code>
directive.
</p>

<h2 id="noscript-redirect">Why is PageSpeed inserting a meta refresh to
/?PageSpeed=noscript or /?ModPagespeed=noscript at the top of the page?</h2>
<p>
The <code><a href="filter-js-defer">defer_javascript</a></code>,
<code><a href="filter-lazyload-images">lazyload_images</a></code>,
<code><a href="filter-dedup-inlined-images">dedup_inlined_images</a></code>, and
<code><a href="filter-local-storage-cache">local_storage_cache</a></code>
filters require JavaScript to render pages correctly. To support clients that
have JavaScript disabled, if any of these filters are enabled, PageSpeed will
insert a meta refresh inside a <code>noscript</code> tag at the top of the page.
This meta refresh will redirect clients with JavaScript disabled to the current
URL with a '<code>?PageSpeed=noscript</code>' query parameter appended which
disables filters that require JavaScript.
</p>
<p>
If you wish to disable this redirect, for instance if your page already requires
JS to function correctly, set the following option in your
<code>pagespeed.conf</code>:
<dl>
  <dt>Apache:<dd><pre class="prettyprint"
     >ModPagespeedSupportNoScriptEnabled false</pre>
  <dt>Nginx:<dd><pre class="prettyprint"
     >pagespeed SupportNoScriptEnabled false;</pre>
</dl>
</p>


<h2 id="collapse-newlines">Why won't the <code>collapse_whitespace</code> filter
remove newlines?</h2>

<p>
When removing whitespace from HTML, some website optimizers remove newlines
entirely, but PageSpeed leaves them in.  This isn't actually a problem with newlines,
however, it's that it's not generally safe to remove a run of whitespace
entirely.  You can turn any number of consecutive whitespace characters into a
single one, and we do that, but removing the whole run can make the site render
differently.
</p>

<p>
To take a simple example, consider:
</p>

<pre>
    &lt;body&gt;
      &lt;h1&gt;Hello World&lt;/h1&gt;
      Lorem     ipsum       dolor sit amet, consectetur
      adipiscing elit. Fusce molestie ante &lt;b&gt;vitae&lt;/b&gt;
      iaculis         varius. ...
    &lt;/body&gt;
</pre>

<p>
PageSpeed with <code>collapse_whitespace</code> will turn this into:
</p>

<pre>
&lt;body&gt;
&lt;h1&gt;Hello World&lt;/h1&gt;
Lorem ipsum dolor sit amet, consectetur
adipiscing elit. Fusce molestie ante &lt;b&gt;vitae&lt;/b&gt;
iaculis varius. ...
&lt;/body&gt;
</pre>

<p>
If PageSpeed went further and put it all on one line, it would be
converting <code>&lt;b&gt;vitae&lt;/b&gt; iaculis</code>
into <code>&lt;b&gt;vitae&lt;/b&gt;iaculis</code>, which would change the
rendering from "<b>vitae</b> iaculis" into "<b>vitae</b>iaculis"; one word
instead of two.  It would have been safe to turn <code>&lt;body&gt;
&lt;h1&gt;Hello World&lt;/h1&gt;</code> into <code>&lt;body&gt;&lt;h1&gt;Hello
World&lt;/h1&gt;</code>, but doing one and not the other requires understanding
the CSS (and JS) to the point where we can reliably tell that one pair of
elements are <code>display:&nbsp;block</code> while the other pair
are <code>display:&nbsp;inline</code>.
</p>

<h2 id="warning-fetch-rate">I've got a warning saying
"Serf fetch failure rate extremely high". What does this mean?</h2>

<p>The warning means that, when PageSpeed tried to fetch resources inside your
web page for optimization, over 50% of attempts inside a 30-minute period
failed. This may just mean you have some broken resource includes in your
pages (in which case, it may be a good idea to fix them for better performance),
but might indicate that PageSpeed's fetching is not working properly. If you
have in-place resource optimization on, that can result in user requests for
<code>.pagespeed.</code> URLs returning error 404 intermittently.</p>

<p>First of all, check to see if the log mentions anything else about fetch
trouble. If what's there is not helpful, the root cause may be more obvious
if you follow these steps:</p>
<ol>
<li>Disable <a href="system#ipro">in-place resource optimization</a> temporarily.
    </li>
<li>Clear PageSpeed cache.</li>
<li>Open a test page with a <code>?PagespeedFilters=+debug</code> query
   parameter, reload it a few times, and see if resources are getting optimized,
   and if not if there is an error message.
<li>Revert the config changes.</li>
</ol>

<p>Most likely you may need to configure an <a href="domains#mapping_origin">
origin domain, to specify the host or IP to talk to fetch resources.</p>

<p>You may also want to consider using <a href="domains#ModPagespeedLoadFromFile">
<code>LoadFromFile</code></a> functionality, as that performs much better if
your resources are static.</p>

<h2 id="varying-results">Sometimes pages are served as partially optimized. How can
I achieve a more steady optimization ouput?</h2>

<p>There are two (relatively) common situations that may lead up to a fluctuating
level of optimization in the output:
<ol>
<li>Low traffic, combined with short http expiry times for image, css and javascript
responses: <br/>
Consider increasing the http expiry applied to the original
resources, or set up <a href="domains#ModPagespeedLoadFromFile">LoadFromFile</a>
to allow the module to load static files directly from disk.</li>
<li>High cache churn rates:<br/>
If PageSpeed's caches are sized too small, optimized assets falling out of the cache
may cause frequent reoptimization. <a href="system#caching">Sizing the cache</a> to 3
to 4 times the size of the original assets of the website should allow the module to
cache all the original resources plus multiple optimized variants (for serving 
different user-agents and screen sizes).
</li>
<li>If the above did not help, the <a href="admin">admin pages</a> offer various tools
that may assist in diagnosing what happens.</li>
</ol>

</p>
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