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.\" SPDX-License-Identifier: BSD-2-Clause
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.\" Copyright (c) 2022 Michael Tuexen <tuexen@FreeBSD.org>
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.Dd January 14, 2024
.Dt TCPSSO 8
.Os
.Sh NAME
.Nm tcpsso
.Nd set a socket option on a TCP endpoint
.Sh SYNOPSIS
.Nm
.Fl i Ar id
.Op Ar level
.Ar optname
.Ar optval
.Nm
.Fl a
.Op Ar level
.Ar optname
.Ar optval
.Nm
.Fl C Ar cc-algo
.Op Fl S Ar stack
.Op Fl s Ar state
.Op Ar level
.Ar optname
.Ar optval
.Nm
.Op Fl C Ar cc-algo
.Fl S Ar stack
.Op Fl s Ar state
.Op Ar level
.Ar optname
.Ar optval
.Nm
.Op Fl C Ar cc-algo
.Op Fl S Ar stack
.Fl s Ar state
.Op Ar level
.Ar optname
.Ar optval
.Sh DESCRIPTION
The
.Nm
command applies a
.Ar level
level socket option with name
.Ar optname
and value
.Ar optval
on a TCP endpoint from the command line.
.Pp
TCP endpoints in the
.Dv SYN_RCVD
state can only be handled by
.Nm
if their prior state was
.Dv SYN_SENT .
.Pp
.Op Ar level
can be specified as a non-negative number or a symbolic name like
.Dv SOL_SOCKET ,
.Dv IPPROTO_IP ,
.Dv IPPROTO_IPV6 ,
or
.Dv IPPROTO_TCP .
If not specified,
.Nm
deduces the level from
.Ar optname ,
if provided as a symbolic name.
If that is not the case,
.Dv IPPROTO_TCP
is used.
.Pp
.Ar optname
can be specified as a non-negative number or a symbolic name like
.Dv SO_DEBUG ,
.Dv IP_TOS ,
.Dv IPV6_TCLASS ,
.Dv TCP_LOG ,
.Dv TCP_CONGESTION ,
or
.Dv TCP_FUNCTION_BLK .
.Pp
.Ar 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
.Ar optname
is
.Dv TCP_FUNCTION_BLK
then
.Ar optval
is converted to a
.Vt "struct tcp_function_set" .
.Pp
If
.Fl i Ar id
is specified then
.Nm
will apply the socket option to the TCP endpoint with the
.Dv inp_gencnt
provided as
.Ar id .
The
.Dv inp_gencnt
for existing TCP endpoints can be determined by using
.Xr sockstat 1 .
.Pp
If
.Fl a
is specified then
.Nm
will apply the socket option to all TCP endpoints subject to the above state
restrictions.
.Pp
If
.Fl C Ar cc-algo
is specified then
.Nm
will apply the socket option to all TCP endpoints using the TCP
congestion control algorithm
.Ar cc-algo
and subject to the above state restrictions.
.Pp
If
.Fl S Ar stack
is specified then
.Nm
will apply the socket option to all TCP endpoints using the TCP
stack
.Ar stack
and subject to the above state restrictions.
.Pp
If
.Fl s Ar state
is specified then
.Nm
will apply the socket option to all TCP endpoints being in the state
.Ar state .
.Ar state
is one of
.Dv CLOSED ,
.Dv LISTEN ,
.Dv SYN_SENT ,
.Dv SYN_RCVD ,
.Dv ESTABLISHED ,
.Dv CLOSE_WAIT ,
.Dv FIN_WAIT_1 ,
.Dv CLOSING ,
.Dv LAST_ACK ,
.Dv FIN_WAIT_2,
or
.Dv TIME_WAIT .
Using
.Dv SYN_RCVD
only applies to TCP endpoints in the state
.Dv SYN_RCVD
if their prior state was
.Dv SYN_SENT .
.Pp
If multiple of
.Fl C Ar cc-algo ,
.Fl S Ar stack ,
and
.Fl s Ar state
are specified,
.Nm
will apply the socket option to all TCP endpoints using the congestion
control algorithm
.Ar cc-algo ,
being in the state
.Ar state ,
and using the TCP stack
.Ar stack ,
if specified.
.Pp
If none of the
.Fl a ,
.Fl C ,
.Fl S ,
or
.Fl s
options are specified then the option
.Fl i
must be specified.
.Sh EXIT STATUS
.Ex -std
.Sh EXAMPLES
To diagnose a problem with a particular TCP connection to
.Xr sshd 8 ,
first determine its
.Dv inp_gencnt
using
.Xr sockstat 1 :
.Bd -literal -offset indent
# sockstat -4 -c -i -p 22 -P tcp -q
root     sshd       827   4  tcp4 \e
	192.168.1.1:22        192.168.1.2:53736     435
.Ed
.Pp
Then, use the following command to enable Black Box Logging on it:
.Bd -literal -offset indent
# tcpsso -i 435 TCP_LOG 4
.Ed
.Pp
To switch all TCP endpoints from using the freebsd stack to the rack stack use:
.Bd -literal -offset indent
# tcpsso -S freebsd TCP_FUNCTION_BLK rack
.Ed
.Pp
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:
.Bd -literal -offset indent
# tcpsso -C cubic TCP_CONGESTION newreno
.Ed
.Sh SEE ALSO
.Xr sockstat 1 ,
.Xr setsockopt 2 ,
.Xr tcp 4 ,
.Xr tcp_functions 9
.Sh HISTORY
The
.Nm
command first appeared in
.Fx 14 .
.Sh AUTHORS
.An Michael Tuexen Aq Mt tuexen@FreeBSD.org