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TCPSSO(8) FreeBSD System Manager's Manual TCPSSO(8) NAME tcpsso - set a socket option on a TCP endpoint SYNOPSIS tcpsso -i id [level] optname optval tcpsso -a [level] optname optval tcpsso -C cc-algo [-S stack] [-s state] [level] optname optval tcpsso [-C cc-algo] -S stack [-s state] [level] optname optval tcpsso [-C cc-algo] [-S stack] -s state [level] optname optval DESCRIPTION The tcpsso command applies a level level socket option with name optname and value optval on a TCP endpoint from the command line. TCP endpoints in the SYN_RCVD state can only be handled by tcpsso if their prior state was SYN_SENT. [level] can be specified as a non-negative number or a symbolic name like SOL_SOCKET, IPPROTO_IP, IPPROTO_IPV6, or IPPROTO_TCP. If not specified, tcpsso deduces the level from optname, if provided as a symbolic name. If that is not the case, IPPROTO_TCP is used. optname can be specified as a non-negative number or a symbolic name like SO_DEBUG, IP_TOS, IPV6_TCLASS, TCP_LOG, TCP_CONGESTION, or TCP_FUNCTION_BLK. optval can be an integer value, which will be converted to a binary value and passed as an int value. If it cannot be parsed as an integer value, it will be processed as a string. If the optname is TCP_FUNCTION_BLK then optval is converted to a struct tcp_function_set. If -i id is specified then tcpsso will apply the socket option to the TCP endpoint with the inp_gencnt provided as id. The inp_gencnt for existing TCP endpoints can be determined by using sockstat(1). If -a is specified then tcpsso will apply the socket option to all TCP endpoints subject to the above state restrictions. If -C cc-algo is specified then tcpsso will apply the socket option to all TCP endpoints using the TCP congestion control algorithm cc-algo and subject to the above state restrictions. If -S stack is specified then tcpsso will apply the socket option to all TCP endpoints using the TCP stack stack and subject to the above state restrictions. If -s state is specified then tcpsso will apply the socket option to all TCP endpoints being in the state state. state is one of CLOSED, LISTEN, SYN_SENT, SYN_RCVD, ESTABLISHED, CLOSE_WAIT, FIN_WAIT_1, CLOSING, LAST_ACK, FIN_WAIT_2, or TIME_WAIT. Using SYN_RCVD only applies to TCP endpoints in the state SYN_RCVD if their prior state was SYN_SENT. If multiple of -C cc-algo, -S stack, and -s state are specified, tcpsso will apply the socket option to all TCP endpoints using the congestion control algorithm cc-algo, being in the state state, and using the TCP stack stack, if specified. To diagnose a problem with a particular TCP connection to sshd(8), first determine its inp_gencnt using sockstat(1): # sockstat -4 -c -i -p 22 -P tcp -q root sshd 827 4 tcp4 \ 192.168.1.1:22 192.168.1.2:53736 435 Then, use the following command to enable Black Box Logging on it: # tcpsso -i 435 TCP_LOG 4 To switch all TCP endpoints from using the freebsd stack to the RACK stack use: # tcpsso -S freebsd TCP_FUNCTION_BLK rack Switch all TCP endpoints in the LISTEN state to the RACK stack by using: # tcpsso -s LISTEN TCP_FUNCTION_BLK rack The following command will set the congestion control module of all TCP endpoints currently using cubic as its congestion control algorithm to the congestion control algorithm newreno: # tcpsso -C cubic TCP_CONGESTION newreno SEE ALSO sockstat(1), setsockopt(2), tcp(4), tcp_functions(9) HISTORY The tcpsso command first appeared in FreeBSD 14. AUTHORS Michael Tuexen <tuexen@FreeBSD.org> FreeBSD 14.2-RELEASE August 3, 2024 FreeBSD 14.2-RELEASE