The connection tracking mechanism in Linux is the foundation of many network applications, it may affect our connection establishment.

In some situations, even if the total number of MQTT connections on the current server has not reached the maximum limit of file descriptors, the client's connection request still fails, and we will observe the count of Overflowed and SYN Dropped continuously increasing in the OS.

While testing the performance of EMQX, if the number of client connections reaches a large number, you may find that EMQX cannot accept more connections. In this article, we will introduce how to modify kernel parameters to increase the number of file descriptors that EMQX can use on Linux.