If the dynamic shared memory segment type is POSIX thendynamic shared memory control segment in your case it is PostgreSQL.1511679208is stored in /dev/shm
The file you mentioned will be created at the time of PostgreSQL startup and cleared automatically on successful shutdown.
Complete case study depicted your error is found here
I have set the dynamic_shared_memory_type to none which was set as POSIX. For now we are not seeing the error... Can someone please explain what is the impact of setting it as none .