NAME

       tcpaccept - Trace TCP retransmits and TLPs. Uses Linux eBPF/bcc.

SYNOPSIS

       tcpaccept [-h] [-l]

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).

       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.

OPTIONS

       -h     Print usage message.

       -l     Include tail loss probe attempts (in some cases the kernel may not complete the TLP send).

EXAMPLES

       Trace TCP retransmits:
              # tcpretrans

       Trace TCP retransmits and TLP attempts:
              # tcpconnect -l

FIELDS

       TIME   Time of the retransmit.

       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.

       IP     IP address family (4 or 6).

       LADDR  Local IP address.

       LPORT  Local port.

       T>     Type of event: R> == retransmit, L> == tail loss probe.

       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 bcc.

              https://github.com/iovisor/bcc

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

OS

       Linux

STABILITY

       Unstable - in development.

AUTHOR

       Brendan Gregg

SEE ALSO

       tcpconnect(8), tcpaccept(8)