Linux users are typically configured with a maximum number of files to be opened. This is describe at
based upon your installation method.
To monitor how many open files a user has one can run
lsof -u <user>
replacing with the linux username who started the Neo4j process.
To understand the limits for said one can also run
replacing with the linux processID for the running Neo4j process.
This will produce output similar to
Limit Soft Limit Hard Limit Units
Max cpu time unlimited unlimited seconds
Max file size unlimited unlimited bytes
Max data size unlimited unlimited bytes
Max stack size 8388608 unlimited bytes
Max core file size 0 unlimited bytes
Max resident set unlimited unlimited bytes
Max processes 31357 31357 processes
Max open files 40000 40000 files