Can you debug a site with Drush? I have 3 Drupal 8 sites. 2 have premium themes and one is Bartik themed.

When I built the 2 the sites with premium themes in Ubuntu I could log in fine but when I log in to them when online (CentOS server) the sites crashes with the error:


  The website encountered an unexpected error. Please try again later.


This doesn't happen with the Bartik site.

I wonder if I could debug the problem somehow with Drush or if there is anything else than drush wd-show just to make sure I cover the most I can with it?

The only way I know to debug problems with drush is drush wd-show.

Is there any command that could help me understand why site logins fail on that particular environment?

Update - Error from Drush &amp; Cpanel error log:


  [Tue Jul 19 14:50:11.393827 2016] [:error] [pid 15721] [client
  79.177.142.239:33948] Uncaught PHP Exception RuntimeException: "Failed to start the session because headers have already been sent by
  "/home/zantech0/public_html/yoursitename.com/themes/business/includes/skins-menu/skins_menu.inc"
  at line 2."
  
  at
  /home/zantech0/public_html/yoursitename.com/vendor/symfony/http-foundation/Session/Storage/NativeSessionStorage.php
  line 140, referer: http://yoursitename.com/user/login


Head of the file:
That error is often caused by PHP files that generate output they should not. Generally it's caused by errors like having a closing ?> and then a blank line at the end of the file. It's possible that a blank line was added during whatever process you used to move the file to the production server (git, lots of editors, and a few FTP clients will sometimes do this automatically).

In your case I would check /home/zantech0/public_html/yoursitename.com/themes/business/includes/skins-menu/skins_menu.inc to see if it does something that generates output (and therefore triggers PHP to send response headers).