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 usually not, since
       retransmits are usually sent by the kernel on timeouts). To keep
       overhead very low, only the TCP retransmit 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 traversing.

       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  Local IP address.

       LPORT  Local port.

       RADDR  Remote IP address.

       RPORT  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/iovisor/bpftrace

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

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

              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)