Troubleshooting Crawler Issues

Too Many Pages Added to Blacklist

Particular pages are being added to the blacklist after the first crawling, but when you check manually (through the browser or through curl) you see the x-litespeed-cache header and 200 OK status code. So, why are the URIs ending up in the blacklist?

By default , LSCWP's built-in crawler will add a URI to the blacklist if the following conditions are met:

  1. The page is not cacheable by design or by default. In other words, any pages that send the response header x-litespeed-cache-control: no-cache
  2. The page doesn't respond with any of the following headers:
    • HTTP/1.1 200 OK
    • HTTP/1.1 201 Created
    • HTTP/2 200
    • HTTP/2 201

Let's look at the second case, in particular.


The steps below explain how to diagnose a timeout problem. If you wanted to, you could skip all of this and simply increase the timeout to see if that makes a difference. Navigate to LiteSpeed Cache > Crawler > General Settings and set Timeout to something higher than it is. The default is 30 seconds.

Missing Response Header

You can confirm that you are dealing with a missing response header by checking the debug log. You should see that the response header was never logged.

To figure out why, open the following file: litespeed-cache/lib/litespeed/litespeed-crawler.class.php

Add this code at line 273, to allow LiteSpeed to log more information:

LiteSpeed_Cache_Log::debug( 'crawler logs headers', $headers) ; 

Now, when the crawler processes a URI, the $headers will be written to the debug log.

Run the crawler manually, and run the following command:

grep headers /path/to/wordpress/wp-content/debug.log

You should see something like this:

07/10/19 21:53:28.446 [ 1 nsy] crawler logs headers 'HTTP/1.1 200 OK
07/10/19 21:53:28.447 [ 1 nsy) crawler logs headers ---
07/10/19 21:53:28.448 [ 1 nsy] crawler logs headers 'HTTP/1.1 200 OK 
07/10/19 21:53:38.513 [ 1 nsy] crawler logs headers 'HTTP/1.1 200 OK

In this example, you can see that most of the logs show the header is HTTP/1.1 200 OK but one of them is empty. It's the empty one that is being added to the blacklist.

To further complicate matters, the page looks fine when you curl it:

[root@test ~]# curl -I -XGET
HTTP/1.1 200 OK
Date: Thu, 11 Jul 2019 20:57:54 GMT
Content-Type: text/html; charset=UTF-8
Transfer-Encoding: chunked
Connection: keep-alive
Set-Cookie: __cfduid=some-string-here; expires=Fri, 10-Jul-20 20:57:43 GMT; path=/;; HttpOnly
Cf-Railgun: direct (starting new WAN connection)
Link: <>; rel=""
Link: </min/186a9.css>; rel=preload; as=style,</min/f7e97.css>; rel=preload; as=style,</wp-content/plugins/plugin/jquery.min.js>; rel=preload; as=script,</min/7f44e.js>; rel=preload; as=script,</min/a8512.js>; rel=preload; as=script,</wp-content/plugins/litespeed-cache/js/webfontloader.min.js>; rel=preload; as=script
Set-Cookie: wp_woocommerce_session_string=value; expires=Sat, 13-Jul-2019 20:57:43 GMT; Max-Age=172799; path=/; secure; HttpOnly
Set-Cookie: wp_woocommerce_session_string=value; expires=Sat, 13-Jul-2019 20:57:43 GMT; Max-Age=172799; path=/; secure; HttpOnly
Vary: Accept-Encoding
X-Litespeed-Cache: miss
X-Litespeed-Cache-Control: public,max-age=604800
X-Litespeed-Tag: 98f_WC_T.156,98f_WC_T.494,98f_WC_T.48,98f_product_cat,98f_URL.e3a528ab8c54fd1cf6bf060091288580,98f_T.156,98f_
X-Powered-By: PHP/7.3.6
Expect-CT: max-age=604800, report-uri=""
Server: cloudflare
CF-RAY: 5f5db4fd1c234c56-AMS

This URI returns 200, and x-litespeed-cache-control: public, so it is unclear why the header is empty when crawling.

To figure it out, first you need to find the exact options the PHP curl used, and then apply those options to your own curl command. Add more code to the debug log, instructing it to grab the curl options the crawler used.

Edit litespeed-cache/lib/litespeed/litespeed-crawler.class.php, and add the following at line 627, directly before return $options ;, like so:

$options[ CURLOPT_COOKIE ] = implode( '; ', $cookies ) ;

LiteSpeed_Cache_Log::debug( 'crawler logs headers2', json_encode( $options ) ) ;
return $options ;

Now, manually crawl it again, and you will see something like the following:

07/11/19 14:20:15.374 [ 1 ZWh] crawler logs headers2 --- '{
"10023":["Cache-Control: max-age=0","Host:"],

The numbers you see are PHP curlset reference code. An internet search reveals that the 78 and 13 are particularly interesting. They represent curl connection timeout and curl timeout.

Apply these options to your curl command, like so:

curl -I -XGET --max-time 10

The output looks like this:

curl: (28) Operation timed out after 10001 milliseconds with 0 out of -1 bytes received

This confirms that a timeout is the root cause of the problem. Without cache, the page takes more than ten seconds to load.

Try one more test to confirm it, and format the output in a more readable way:

curl -w 'Establish Connection: %{time_connect}snTTFB: %{time_starttransfer}snTotal: %{time_total}sn' -XGET -A "lscache_runner"
Establish Connection: 0.006s
TTFB: 16.455s
Total: 16.462s

This confirms it. The page without cache takes more than 16 seconds to load, which results in a curl timeout. That is the reason why the debug log shows an empty header, the 200 status is never received by the crawler, and the URL is blacklisted.


Increase the timeout.

Navigate to LiteSpeed Cache > Crawler > General Settings and set the timeout to something greater than 10 seconds (the LSCWP v3.0 default is 30).


It's possible that a timeout is not the reason why the crawler is failing to get a successful response header. The answer can still probably be found in the detailed curl options output. A little bit of research may be required.

Last update: January 20, 2021