netipv4tcpkeepalivetime

The netipv4tcpkeepalivetime parameter is a kernel tunable that controls the idle time before TCP begins sending keepalive probes on a TCP connection. Keepalive probes are small packets sent by the TCP stack to check if the remote end of a connection is still responsive. If no data has been exchanged on a connection for a period specified by netipv4tcpkeepalivetime, the kernel will start sending these probes. This parameter is measured in seconds.

If the remote end does not respond to a keepalive probe after a certain number of retries, the connection is considered dead, and the kernel will notify the application. This helps to clean up stale connections that might otherwise remain open indefinitely. The default value for netipv4tcpkeepalivetime is typically set to two hours (7200 seconds).

Adjusting this value can have implications for network resource usage and application behavior. A shorter keepalive time can help detect dead connections more quickly, which might be beneficial for applications that rely on timely connection status information. However, setting it too low can increase network traffic and potentially lead to premature termination of connections if the network experiences transient issues or if the remote host is temporarily unavailable. Conversely, a longer keepalive time can conserve network resources but may result in applications holding onto dead connections for extended periods.

The netipv4tcpkeepalivetime parameter is part of the Linux kernel's TCP/IP networking stack and can be modified using system administration tools or by writing to the appropriate entry in the /proc filesystem, specifically at /proc/sys/net/ipv4/tcp_keepalive_time.