OpenDJ needs to be able to open many files, especially when handling many client connections. Linux systems in particular often set a limit of 1024 per user, which is too low for OpenDJ.
When setting up OpenDJ for production use, make sure OpenDJ can use
at least use at least 64K (65536) file descriptors. For example when running
OpenDJ as user opendj on a Linux system that uses
/etc/security/limits.conf to set user level limits,
you can set soft and hard limits by adding these lines to the file.
opendj soft nofile 65536 opendj hard nofile 131072
The example above assumes the system has enough file descriptors available overall. You can check the Linux system overall maximum as follows.
$ cat /proc/sys/fs/file-max 204252
