If you’ve upgraded from an older version of Zend Server than 5.6 up to 6.0 you may have ended up with a patched httpd.conf that references a vhost configuration file that has not been created. If you try to start Apache you may see this message:

$ sudo apachectl start
httpd: Syntax error on line 428 of \
/usr/local/zend/apache2/conf/httpd.conf: \
Could not open configuration file \
/usr/local/zend/etc/sites.d/zend-default-vhost-80.conf: \
No such file or directory
-e /usr/sbin/apachectl start [FAILED]

This means your Apache configuration has been patched to references the virtual host files, without actually creating them. If you take a look inĀ /usr/local/zend/apache2/conf/httpd.conf it may look like this:

#ZEND-{D530A88D964D3928787617703831DDA9}
NameVirtualHost *:80
<VirtualHost *:80>
#ZEND-{A5F00F7D0B1F44B6CEDF7CA64E576EC6}
Include "/usr/local/zend/etc/sites.d/zend-default-vhost-80.conf"
#ZEND-{A5F00F7D0B1F44B6CEDF7CA64E576EC6}
</VirtualHost>
#ZEND-{D530A88D964D3928787617703831DDA9}
#ZEND-{ADBE6F7D623A36E39CB1FBD16A356D09}
Include "/usr/local/zend/etc/sites.d/globals-*.conf"
Include "/usr/local/zend/etc/sites.d/vhost_*.conf"
#ZEND-{ADBE6F7D623A36E39CB1FBD16A356D09}

One way to fix this is to simply copy them down from these Gists: