Manual: tcpretrans.bt

tcpretrans.bt(8)				   System Manager's Manual				    tcpretrans.bt(8)

NAME
       tcpretrans.bt - Trace or count TCP retransmits. Uses Linux bpftrace/eBPF

SYNOPSIS
       tcpretrans.bt

DESCRIPTION
       This  traces  TCP retransmits, showing address, port, and TCP state information, and sometimes the PID (although usu‐
       ally not, since retransmits are usually sent by the kernel on timeouts). To keep overhead very low, only the TCP	 re‐
       transmit functions are traced. This does not trace every packet (like tcpdump(8) or a packet sniffer). Optionally, it
       can  count  retransmits	over a user signalled interval to spot potentially dropping network paths the flows are tra‐
       versing.

       This uses dynamic tracing of the kernel tcp_retransmit_skb() and tcp_send_loss_probe() functions, and will need to be
       updated to match kernel changes to these functions.

       Since this uses BPF, only the root user can use this tool.

REQUIREMENTS
       CONFIG_BPF and bcc.  CONFIG_BPF and bpftrace.

EXAMPLES
       Trace TCP retransmits:
	      # tcpretrans.bt

       FIELDS

       TIME   Time of the call, in HH:MM:SS format.

       PID    Process ID that was on-CPU. This is less useful than it might sound, as it may usually be 0, for	the  kernel,
	      for timer-based retransmits.

       LADDR:LPORT
	      Local IP address and local port.

       RADDR:RPORT
	      Remote IP address and remote port.

       STATE  TCP session state.

OVERHEAD
       Should  be  negligible:	TCP  retransmit	 events should be low (<1000/s), and the low overhead this tool adds to each
       event should make the cost negligible.

SOURCE
       This is from bpftrace

	      https://github.com/bpftrace/bpftrace

       Also look in the bpftrace distribution for a companion _examples.txt file containing example usage, output, and	com‐
       mentary for this tool.

       This  is	 a  bpftrace  version of the bcc tool of the same name. The bcc tool may provide more options and customiza‐
       tions.

	      https://github.com/iovisor/bcc

OS
       Linux

STABILITY
       Unstable - in development.

AUTHOR
       Brendan Gregg, adapted for bpftrace by Dale Hamel

SEE ALSO
       tcpconnect.bt(8), tcpaccept.bt(8)

USER COMMANDS						 2018-11-24					    tcpretrans.bt(8)