# Headers have already been sent

**URL:** <https://forum.mautic.org/t/headers-have-already-been-sent/13887>\
**Category:** Product Support\
**Created:** [April 13, 2020, 8:14pm UTC](https://forum.mautic.org/t/headers-have-already-been-sent/13887 "2020-04-13T20:14:52Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![Rich](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.mautic.org/rich/32/45_2.png) [@Rich](https://forum.mautic.org/u/Rich)\
**Post date:** [April 13, 2020, 8:14pm UTC](https://forum.mautic.org/t/headers-have-already-been-sent/13887/1 "2020-04-13T20:14:52Z")

</div>

When attempting to upgrade from Mautic 2.14.2 to Mautic 2.15.3 the process stops with the terminal ( PUTTY) displaying this message

[RuntimeException]  
Failed to start the session because headers have already been sent by “/home/path to mautic/app/AppKernel.php” at line 377.

The upgrade fails and I am unable to access mautic.

Q A

| Mautic version | 2.14.2  
| PHP Version 7.1.33  
| Browser | Chrome

### Steps to reproduce

check if there are any pending database migrations  
php public\_html/mailstudio/messages/app/console doctrine:migration:migrate

verify database schema  
php public\_html/mailstudio/messages/app/console doctrine:schema:update --force

Correct any issues before proceeding

per article on [https://mauteam.org/](https://mauteam.org/)

~ Contending with the error “…max 64 keys allowed” execute the following command  
~ php public\_html/mailstudio/messages/app/console doctrine:schema:update --dump-sql

manually execute the remaining queries on the database using PHPMyAdmin.  
worked with on issue Adrian Urso [@fakir22](https://github.com/fakir22) to resolve issues. see item [#6063](https://github.com/mautic/mautic/issues/6063)

All issues cleared!

~ clear the Mautic cache:  
php public\_html/mailstudio/messages/app/console cache:clear

Visit Mautic UI to check if everything is running properly

Check  
1.) Mautic logs ~~~/home/pathe to mautic/app/logs~~~ ++ no errors  
2.) Apache logs ++ no errors  
3.) PHP logs ++ no errors

~run php app/console mautic:update:find

~run php app/console mautic:update:apply  
error message on terminal is

[RuntimeException]  
Failed to start the session because headers have already been sent by “/home/path to mautic/app/AppKernel.php” at line 377.

in php log it is [2020-04-13 12:49:11] mautic.NOTICE: RuntimeException: Failed to start the session because headers have already been sent by “/path to mautic/app/AppKernel.php” at line 377. (uncaught exception) at /path to mautic/vendor/symfony/http-foundation/Session/Storage/NativeSessionStorage.php line 151 while running console command `mautic:update:apply`