## ListenBacklog

Syntax: ListenBacklog backlog
Default: `ListenBacklog 511`
Context: server config
Status: Core
Compatibility: ListenBacklog is only available in Apache versions after 1.2.0.

The maximum length of the queue of pending connections. Generally no tuning is needed or desired, however on some systems it is desirable to increase this when under a TCP SYN flood attack. See the backlog parameter to the `listen(2)` system call.

This will often be limited to a smaller number by the operating system. This varies from OS to OS. Also note that many OSes do not use exactly what is specified as the backlog, but use a number based on (but normally larger than) what is set.