Today my apache2 suddenly didn't run.cat /var/www/html/info.php<?phpecho phpinfo();?>No output, no error info at all, no result when to input http://127.0.0.1/info.php in Firefox.cat  /var/log/apache2/error.logNothing!!What is the matter with my apache2? service apache2 restartAnd then to input http://127.0.0.1/info.php in Firefox, cat  /var/log/apache2/error.log[Fri Sep 18 16:06:54.065576 2015] [mpm_event:notice] [pid 16124:tid 139930869675904] AH00491: caught SIGTERM, shutting down[Fri Sep 18 16:06:55.182391 2015] [mpm_event:notice] [pid 20296:tid 139659549255552] AH00489: Apache/2.4.10 (Debian) configured -- resuming normal operations[Fri Sep 18 16:06:55.182555 2015] [core:notice] [pid 20296:tid 139659549255552] AH00094: Command line: '/usr/sbin/apache2'No output,no error info ,no result in the Firefox as before. 
What is the matter with my apache?
apache httpd;php