[warning] session_id(): Cannot change session id when headers already sent AbstractProxy.php:94

Thanks for the feedback.

Please, provide more info regarding PHP version.

Remove not related issue

As a warning it should not have broken anything. Can @zenimagine provide more information about how the update was performed for example:

• php version
• using Drush/Console or UI
• if using Drush/Console which version

Ah looking at the screenshots Drush is being used. We tackled something similar before in #2901753: [PHP 7.2] DrupalKernel.php: ini_set(): Headers already sent. The question is why is this being invoked from the CLI.

@zenimagine I've done the update with only Drupal core standard profile and Drush on PHP 7.2 and I don't get the error. Maybe some module you have is causing this. What version of Drush are you using? I'm on 9.4.0

So yep this has been fixed in Drush 9.4.0. It does not happen with that version but does with 9.0.0-beta3. Confirmed by testing locally and seeing the exact same warning. I don't see the warning with the currently support version of Drush.

Still getting this error with Drush 10

Just like #11, I'm receiving this error too:
PHP 7.3.13
Drush 10.2

UPDATE:
looks like I didn't end my php tag in an empty .module file

I ran into this same error. The caused turned out to be an empty blank line accidentally inserted before the <?php tag in one of our settings files.

@PCate thank you! After an accidental edit to a .module file we hit this - there was a space above the <?php tag.

Drupal 8.9.1, Drush 10.2.2
Also encountered an error
[warning] session_id(): Cannot change session id when headers already sent AbstractProxy.php:94
In my custom module there was a space at the very beginning before <?php. After deleting the empty line, the notification disappeared. Thank!

Hi it's me

MY error was the same under Drupal Drupal 8.9.3, Drush 8.1.15 PHP 7.2

[warning] session_id(): Cannot change session id when headers already sent AbstractProxy.php:94

See Picture - I updated the webform module.

there was a space above the <?php tag.
In my custom module there was a space at the very beginning before <?php. After deleting the empty line,

can someone tell me what I should do. (which module ?? and where ??)

Thanks Lothar