Title: PHP Warning: Cannot modify header information Last modified: November 2, 2022 --- # PHP Warning: Cannot modify header information * Resolved [SebastiaanVaz](https://wordpress.org/support/users/sebastiaanvaz/) * (@sebastiaanvaz) * [3 years, 7 months ago](https://wordpress.org/support/topic/php-warning-cannot-modify-header-information-18/) * After updating to WP 6.1, I get the following errors: * [02-Nov-2022 09:51:39 UTC] PHP Warning: Cannot modify header information – headers already sent by (output started at ***/wp-cron.php:30) in ***/wp-content/plugins/ litespeed-cache/src/vary.cls.php on line 735 * The page I need help with: _[[log in](https://login.wordpress.org/?redirect_to=https%3A%2F%2Fwordpress.org%2Fsupport%2Ftopic%2Fphp-warning-cannot-modify-header-information-18%2F%3Foutput_format%3Dmd&locale=en_US) to see the link]_ Viewing 11 replies - 1 through 11 (of 11 total) * Plugin Support [qtwrk](https://wordpress.org/support/users/qtwrk/) * (@qtwrk) * [3 years, 7 months ago](https://wordpress.org/support/topic/php-warning-cannot-modify-header-information-18/#post-16158881) * May I know what is your PHP version ? * Thread Starter [SebastiaanVaz](https://wordpress.org/support/users/sebastiaanvaz/) * (@sebastiaanvaz) * [3 years, 7 months ago](https://wordpress.org/support/topic/php-warning-cannot-modify-header-information-18/#post-16159539) * 8.1 * Thread Starter [SebastiaanVaz](https://wordpress.org/support/users/sebastiaanvaz/) * (@sebastiaanvaz) * [3 years, 6 months ago](https://wordpress.org/support/topic/php-warning-cannot-modify-header-information-18/#post-16172546) * Can you please help? My Debug.log is filled with thousands of these PHP warnings. * Plugin Support [qtwrk](https://wordpress.org/support/users/qtwrk/) * (@qtwrk) * [3 years, 6 months ago](https://wordpress.org/support/topic/php-warning-cannot-modify-header-information-18/#post-16172555) * Hi, * yes, I have reported this to devs for further investigation * best regards, * Thread Starter [SebastiaanVaz](https://wordpress.org/support/users/sebastiaanvaz/) * (@sebastiaanvaz) * [3 years, 6 months ago](https://wordpress.org/support/topic/php-warning-cannot-modify-header-information-18/#post-16184109) * Sometimes this one appears in between the other warning: * [09-Nov-2022 16:54:38 UTC] PHP Warning: Cannot modify header information – headers already sent by (output started at /home/mymoissanite/public_html/staging/wp- cron.php:30) in /home/mymoissanite/public_html/staging/wp-content/plugins/sitepress- multilingual-cms/classes/request-handling/class-wpml-language-per-domain-sso. php on line 123 * Hence, it may have to do with WPML? All versions are updated to latest. * Thread Starter [SebastiaanVaz](https://wordpress.org/support/users/sebastiaanvaz/) * (@sebastiaanvaz) * [3 years, 6 months ago](https://wordpress.org/support/topic/php-warning-cannot-modify-header-information-18/#post-16192127) * Hello. Could you provide any updates? * [Robertiks](https://wordpress.org/support/users/robert22/) * (@robert22) * [3 years, 4 months ago](https://wordpress.org/support/topic/php-warning-cannot-modify-header-information-18/#post-16366411) * I get the same problem. Php version 8.1 * PHP Warning: Cannot modify header information – headers already sent by (output started at /home/****/public_html/wp-cron.php:30) in /home/*****/public_html/ wp-content/advanced-headers.php on line 35 * FYI: advanced-headers.php file is generated by really simple ssl PRO * I use latest litespeed plugin ( version 5.3.2 ) and in cpanel: 6.0.12 (build 13) * Please advise. * UPDATE: After further investigation it seems this is a long reported bug: [https://bugs.php.net/bug.php?id=75946&edit=2](https://bugs.php.net/bug.php?id=75946&edit=2) * The problem will only show if you are running wp-cron through a wget/curl request. If you are instead using a local cron job and calling it directly through php, there is no request so no headers and no issue. - This reply was modified 3 years, 4 months ago by [Robertiks](https://wordpress.org/support/users/robert22/). * [usabe](https://wordpress.org/support/users/usabe/) * (@usabe) * [3 years, 4 months ago](https://wordpress.org/support/topic/php-warning-cannot-modify-header-information-18/#post-16419707) * Hi [@sebastiaanvaz](https://wordpress.org/support/users/sebastiaanvaz/) * I just checked with our support team regarding this issue. Basically we could not reproduce this purposefully at this moment. I saw different users were complaining about this as well in the past topics. To help us figure this out, could you please open a ticket by emailing to [support@litespeedtech.com](https://wordpress.org/support/topic/php-warning-cannot-modify-header-information-18/support@litespeedtech.com?output_format=md) with some further details? We may need to work closer with you to find out the root cause. * Please remember to reference this topic and ask to assign your ticket to Abe. I will check into this further from there. * [Nils](https://wordpress.org/support/users/nilsbosman/) * (@nilsbosman) * [3 years, 3 months ago](https://wordpress.org/support/topic/php-warning-cannot-modify-header-information-18/#post-16465996) * I can confirm [@robert22](https://wordpress.org/support/users/robert22/) findings. Running WP 6.1, PHP 8.1, LSCWP 5.3.2. This issue indeed only pops-up when running cron via the server with wget/curl. Is there any progress on this issue? * Plugin Support [qtwrk](https://wordpress.org/support/users/qtwrk/) * (@qtwrk) * [3 years, 3 months ago](https://wordpress.org/support/topic/php-warning-cannot-modify-header-information-18/#post-16466038) * this issue will be patched in next release 🙂 * [Nils](https://wordpress.org/support/users/nilsbosman/) * (@nilsbosman) * [3 years, 3 months ago](https://wordpress.org/support/topic/php-warning-cannot-modify-header-information-18/#post-16466198) * Great! Thanks for the update! Viewing 11 replies - 1 through 11 (of 11 total) The topic ‘PHP Warning: Cannot modify header information’ is closed to new replies. * ![](https://ps.w.org/litespeed-cache/assets/icon-256x256.png?rev=2554181) * [LiteSpeed Cache](https://wordpress.org/plugins/litespeed-cache/) * [Frequently Asked Questions](https://wordpress.org/plugins/litespeed-cache/#faq) * [Support Threads](https://wordpress.org/support/plugin/litespeed-cache/) * [Active Topics](https://wordpress.org/support/plugin/litespeed-cache/active/) * [Unresolved Topics](https://wordpress.org/support/plugin/litespeed-cache/unresolved/) * [Reviews](https://wordpress.org/support/plugin/litespeed-cache/reviews/) * 11 replies * 5 participants * Last reply from: [Nils](https://wordpress.org/support/users/nilsbosman/) * Last activity: [3 years, 3 months ago](https://wordpress.org/support/topic/php-warning-cannot-modify-header-information-18/#post-16466198) * Status: resolved