tcpretrans.bt(8) System Manager's Manual tcpretrans.bt(8)
NAME
tcpretrans.bt - Trace or count TCP retransmits. Uses Linux bpf-
trace/eBPF
SYNOPSIS
tcpretrans.bt
DESCRIPTION
This traces TCP retransmits, showing address, port, and TCP state in-
formation, and sometimes the PID (although usually not, since retrans-
mits 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)
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