file: /proc/sys/net/ipv4/tcp_base_mss
variable: net.ipv4.tcp_base_mss
Official reference

The initial value of search_low to be used by the packetization layer Path MTU discovery (MTU probing). If MTU probing is enabled, this is the initial MSS used by the connection.

tcp_congestion_control - STRING Set the congestion control algorithm to be used for new connections. The algorithm “reno” is always available, but additional choices may be available based on kernel configuration. Default is set as part of kernel configuration. For passive connections, the listener congestion control choice is inherited. [see setsockopt(listenfd, SOL_TCP, TCP_CONGESTION, “name” …) ]