When I tried to access my site, suddenly I could not access it anymore. I checked my error log and found this.[Sun Jul 19 03:10:01.233369 2015] [auth_digest:notice] [pid 2570] AH01757: generating secret for digest authentication ...[Sun Jul 19 03:10:01.233948 2015] [lbmethod_heartbeat:notice] [pid 2570] AH02282: No slotmem from mod_heartmonitor[Sun Jul 19 03:10:01.250268 2015] [mpm_prefork:notice] [pid 2570] AH00163: Apache/2.4.12 (Amazon) PHP/5.4.41 configured -- resuming normal operations[Sun Jul 19 03:10:01.250288 2015] [core:notice] [pid 2570] AH00094: Command line: '/usr/sbin/httpd'[Mon Jul 20 01:16:46.175258 2015] [suexec:notice] [pid 2567] AH01232: suEXEC mechanism enabled (wrapper: /usr/sbin/suexec)[Mon Jul 20 01:16:46.198570 2015] [auth_digest:notice] [pid 2570] AH01757: generating secret for digest authentication ...[Mon Jul 20 01:16:46.199282 2015] [lua:error] [pid 2570] (17)File exists: AH02665: mod_lua: Failed to create shared memory segment on file /tmp/httpd_lua_shm.2570[Mon Jul 20 01:16:46.199302 2015] [:emerg] [pid 2570] AH00020: Configuration Failed, exitingThen, I tried to restart the httpd service. I saw thisStopping httpd:                  [  Failed ]Starting httpd:                  [  OK  ]After restarting the service, I can now access again my site.What seems to be the problem here? I'm sure that I did not touch or restart the server. Can somebody explain what I have experienced, and how can I prevent it from happening again? I don't what my users to find they can't access my site.   Here is some relevant info:Server version: Apache/2.4.12 (Amazon)Server built:   Mar 18 2015 20:24:15
Httpd service suddenly stopped
linux;apache httpd