I have downloaded version 1.5.8 of Grav Core + Admin. I am using apache2 on debian stretch on Google Cloud Platform, with php version 7.0.33.
After unzipping grav-admin, if I move the entire folder into /var/www/html/grav-admin, it works using that directory and I am prompted to set up the admin access at site.com/admin. However, if I move all the files/folders from grav-admin into /var/www/html, the site.com/admin page is a 404.
Here are the contents of grav.log:
[2019-02-24 04:32:41] grav.CRITICAL: Failed to start session: session_start() expects parameter 1 to be array, null given - Trace: #0 /var/www/html/system/src/Grav/Common/Session.php(35): Grav\Framework\Session\Session->start() #1 /var/www/html/system/src/Grav/Common/Processors/InitializeProcessor.php(40): Grav\Common\Session->init() #2 /var/www/html/system/src/Grav/Common/Grav.php(131): Grav\Common\Processors\InitializeProcessor->process() #3 /var/www/html/system/src/Grav/Common/Grav.php(370): Grav\Common\Grav->Grav\Common\{closure}() #4 [internal function]: Grav\Common\Grav::Grav\Common\{closure}('init', 'Initialize', Object(Closure)) #5 /var/www/html/system/src/Grav/Common/Grav.php(346): call_user_func_array(Object(Closure), Array) #6 /var/www/html/system/src/Grav/Common/Grav.php(132): Grav\Common\Grav->__call('measureTime', Array) #7 /var/www/html/index.php(54): Grav\Common\Grav->process() #8 {main} [] []