TCPKEEPIDLE

TCPKEEPIDLE is a TCP socket option that controls the time a TCP connection can remain idle before the system starts sending keepalive probes. Keepalive probes are small packets sent by one side of a connection to verify that the other side is still responsive. If no data has been sent or received over the connection for a duration specified by TCPKEEPIDLE, the system will begin transmitting these probes. This helps detect and close connections that have become effectively dead, such as when a client crashes or a network link fails without proper notification.

The value of TCPKEEPIDLE is typically specified in seconds. Once the idle period defined by TCPKEEPIDLE has passed, the system will then send keepalive probes at intervals defined by another related TCP option, TCPKEEPINTVL, until an acknowledgment is received or a maximum number of probes, defined by TCPKEEPCNT, has been sent. If all probes are sent without a response, the connection is considered broken, and the application using the socket is typically notified with an error.

Setting TCPKEEPIDLE to a very low value can lead to increased network traffic and potential false positives if temporary network congestion or slow responses occur. Conversely, a very high value means that dead connections might remain open for a long time, consuming resources and potentially preventing new connections. The appropriate value for TCPKEEPIDLE depends on the application's requirements for responsiveness and tolerance for stale connections.