How to fix zPanel blank-screen error?

Tracing the problem

Login to the zPanel server using SSH and monitor the apache error log in real-time using the command,

tail -f /var/log/apache2/error.log | grep xx.xx.xx.xx

Note : The IP xx.xx.xx.xx  is your public IP

Now open the zPanel page in web browser which shows error. Return to the error log screen and find the line matching as below,

[Sat Aug 17 03:35:54 2013] [error] [client xx.xx.xx.xx] PHP Warning: system() has been disabled for security reasons in /etc/zpanel/panel/modules/dns_manager/code/controller.ext.php on line 1674, referer: http://IP/?module=dns_manage

From the above error log, it is clear the issue is related to the PHP function system(), which is disabled. Other functions like exec() will also cause the white-screen errors.

Allowing the PHP function()
Edit the Apache Virtual Host configuration file,

vi /etc/zpanel/configs/apache/httpd-vhosts.conf

Note: Please keep a backup copy of httpd-vhosts.conf before editing in case if something went wrong!

Find the VirtualHost entry for the Control Panel,

# Configuration for ZPanel control panel.
<VirtualHost *:80>
ServerAdmin admin@hosting.com
DocumentRoot “/etc/zpanel/panel/”
php_admin_value suhosin.executor.func.blacklist “passthru, show_source, shell_exec, system, pcntl_exec, popen, pclose, proc_open, proc_nice, proc_terminate, proc_get_status, proc_close, leak, apache_child_terminate, posix_kill, posix_mkfifo, posix_setpgid, posix_setsid, posix_setuid, escapeshellcmd, escapeshellarg”
ServerName host.hosting.com
ServerAlias *.host.hosting.com
AddType application/x-httpd-php .php
<Directory “/etc/zpanel/panel/”>
Options FollowSymLinks
AllowOverride All
Order allow,deny
Allow from all
</Directory>
# Custom settings are loaded below this line (if any exist)
</VirtualHost>

php_admin_value suhosin.executor.func.blacklist "passthru, show_source, shell_exec, system, pcntl_exec, popen, pclose, proc_open, proc_nice, proc_terminate, proc_get_status, proc_close, leak, apache_child_terminate, posix_kill, posix_mkfifo, posix_setpgid, posix_setsid, posix_setuid, escapeshellcmd, escapeshellarg"

service apache2 restart