.TH tcptop 8  "2016-09-13" "USER COMMANDS"
.SH NAME
tcptop \- Summarize TCP send/recv throughput by host. Top for TCP.
.SH SYNOPSIS
.B tcptop [\-h] [\-C] [\-S] [\-p PID] [interval] [count]
.SH DESCRIPTION
This is top for TCP sessions.

This summarizes TCP send/receive Kbytes by host, and prints a summary that
refreshes, along other system-wide metrics.

This uses dynamic tracing of kernel TCP send/receive functions, and will
need to be updated to match kernel changes.

The traced TCP functions are usually called at a lower rate than
per-packet functions, and therefore have lower overhead. The traced data is
summarized in-kernel using a BPF map to further reduce overhead. At very high
TCP event rates, the overhead may still be measurable. See the OVERHEAD
section for more details.

Since this uses BPF, only the root user can use this tool.
.SH REQUIREMENTS
CONFIG_BPF and bcc.
.SH OPTIONS
.TP
\-h
Print USAGE message.
.TP
\-C
Don't clear the screen.
.TP
\-S
Don't print the system summary line (load averages).
.TP
\-p PID
Trace this PID only.
.TP
interval
Interval between updates, seconds (default 1).
.TP
count
Number of interval summaries (default is many).
.SH EXAMPLES
.TP
Summarize TCP throughput by active sessions, 1 second refresh:
#
.B tcptop
.TP
Don't clear the screen (rolling output), and 5 second summaries:
#
.B tcptop \-C 5
.TP
Trace PID 181 only, and don't clear the screen:
#
.B tcptop \-Cp 181
.SH FIELDS
.TP
loadavg:
The contents of /proc/loadavg
.TP
PID
Process ID.
.TP
COMM
Process name.
.TP
LADDR
Local address (IPv4), and TCP port
.TP
RADDR
Remote address (IPv4), and TCP port
.TP
LADDR6
Source address (IPv6), and TCP port
.TP
RADDR6
Destination address (IPv6), and TCP port
.TP
RX_KB
Received Kbytes
.TP
TX_KB
Transmitted Kbytes
.SH OVERHEAD
This traces all send/receives in TCP, high in the TCP/IP stack (close to the
application) which are usually called at a lower rate than per-packet
functions, lowering overhead. It also summarizes data in-kernel to further
reduce overhead. These techniques help, but there may still be measurable
overhead at high send/receive rates, eg, ~13% of one CPU at 100k events/sec.
use funccount to count the kprobes in the tool to find out this rate, as the
overhead is relative to the rate. Some sample production servers tested found
total TCP event rates of 4k to 15k per second, and the CPU overhead at these
rates ranged from 0.5% to 2.0% of one CPU. If your send/receive rate is low
(eg, <1000/sec) then the overhead is expected to be negligible; Test in a lab
environment first.
.SH SOURCE
This is from bcc.
.IP
https://github.com/iovisor/bcc
.PP
Also look in the bcc distribution for a companion _examples.txt file containing
example usage, output, and commentary for this tool.
.SH OS
Linux
.SH STABILITY
Unstable - in development.
.SH AUTHOR
Brendan Gregg
.SH INSPIRATION
top(1) by William LeFebvre
.SH SEE ALSO
tcpconnect(8), tcpaccept(8)