httpd fails due to errors related to shared memory when running many instances together

Issue

• We configure many httpd instances together on the same server (more than 5). We cannot run all of these at once as many of them fail to start due to shared memory errors.

• For instance, errors in mod_auth_digest:

  (17)File exists: AH01762: Failed to create shared memory segment on file /path/to/run/authdigest_shm.11230
  [auth_digest:error] [pid 11230:tid 139671784441824] (17)File exists: AH01760: failed to initialize shm - all nonce-count checking, one-time nonces, and MD5-sess algorithm disabled
  

• Or failures in mod_cluster:

  [:emerg] [pid 16982:tid 139835592058848] create_mem_node /path/to/var/cache/manager.node failed: File exists
  :emerg] [pid 16982:tid 139835592058848] AH00020: Configuration Failed, exiting
  

• On in scoreboard files:

  [Wed Feb 20 08:34:44.867814 2019] [core:crit] [pid 21119:tid 139978256164992] (17)File exists: AH00001: unable to create or access scoreboard "/path/to/app/runtime/myserver/server.scoreboard" (name-based shared memory failure)