When I check watchdog, I have lots of PHP warnings like this:

Warning: session_start(): Cannot send session cookie - headers already sent by (output started at /srv/bindings/9c42927e5316467d82a6fb1be50ed34e/code/includes/file.inc:1972) in drupal_session_start() (line 287 of /srv/bindings/9c42927e5316467d82a6fb1be50ed34e/code/includes/session.inc).

There are a lot of reports of errors like this, apparently most of which are caused by having spaces at the beginning or ends of PHP files. But in this case, I think the problem is related to file uploads for the following reason. The Location of these warnings are paths like this:


The Referrer is my "manage pictures" page, which allows users to add a Picture content type which includes an Image field.

So, it looks like session_start() is having trouble during uploads. Is there a standard fix fox this kind of problem?

  • 2
    Those are image style paths, not related to uploads as such. What's happening is that when an image style is requested, a header is being sent before the request has completed, when Drupal sends the headers it's supposed to. It's often caused by a warning/error being written out to the buffer, so try making sure you have all error reporting disabled. The real error should be I your server logs if you're logging then
    – Clive
    May 31, 2015 at 12:35
  • Those look like Pantheon paths? Are the derivatives being made properly? We have run into memory limits there w/ some large images.
    – mpdonadio
    May 31, 2015 at 13:00
  • Stabdard fix? Well I'd start with scanning all files that end with PHP close tag ?>.
    – AKS
    May 31, 2015 at 14:27
  • @MPD Yes, this is on Pantheon. Based on your suggestion, I tried uploading larger images than I usually do, and I was immediately able to reproduce the error. It appears this error appears right after the image is uploaded, on the image page-- the image derivative hasn't been created yet, and then eventually it gets generated, and somehow in that process this error results. Jun 1, 2015 at 15:49

1 Answer 1


I'm also getting the exact same issue on a Pantheon hosted site. This is on a more complex content type (number of fields) with the image field using the multiupload_imagefield_widget module so we can upload multiple images. The error can also appear on removing an image, where the image field is updated via AJAX. Occasionally, a WSOD will occur.

Location or Path always relates to files/styles/....

Tried to duplicate this on a basic content type but it was not occurring. The issue appears on the main content type 80% of the time.

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