tcpretrans.bt(8)

1tcpretrans.bt(8)            System Manager's Manual           tcpretrans.bt(8)
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NAME

6       tcpretrans.bt  -  Trace  or  count  TCP  retransmits.  Uses  Linux bpf‐
7       trace/eBPF
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SYNOPSIS

10       tcpretrans.bt
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DESCRIPTION

13       This traces TCP retransmits, showing address, port, and TCP  state  in‐
14       formation,  and sometimes the PID (although usually not, since retrans‐
15       mits are usually sent by the kernel on timeouts). To keep overhead very
16       low,  only the TCP retransmit functions are traced. This does not trace
17       every packet (like tcpdump(8) or a packet sniffer). Optionally, it  can
18       count  retransmits  over  a user signalled interval to spot potentially
19       dropping network paths the flows are traversing.
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21       This uses  dynamic  tracing  of  the  kernel  tcp_retransmit_skb()  and
22       tcp_send_loss_probe()  functions,  and will need to be updated to match
23       kernel changes to these functions.
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25       Since this uses BPF, only the root user can use this tool.
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REQUIREMENTS

28       CONFIG_BPF and bcc.  CONFIG_BPF and bpftrace.
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EXAMPLES

31       Trace TCP retransmits:
32              # tcpretrans.bt
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35       FIELDS
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37       TIME   Time of the call, in HH:MM:SS format.
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39       PID    Process ID that was on-CPU. This is less useful  than  it  might
40              sound,  as  it may usually be 0, for the kernel, for timer-based
41              retransmits.
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43       LADDR  Local IP address.
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45       LPORT  Local port.
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47       RADDR  Remote IP address.
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49       RPORT  Remote port.
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51       STATE  TCP session state.
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OVERHEAD

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

59       This is from bpftrace
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61              https://github.com/iovisor/bpftrace
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63       Also look in the bpftrace distribution for  a  companion  _examples.txt
64       file containing example usage, output, and commentary for this tool.
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66       This  is  a  bpftrace version of the bcc tool of the same name. The bcc
67       tool may provide more options and customizations.
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69              https://github.com/iovisor/bcc
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OS

72       Linux
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STABILITY

75       Unstable - in development.
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AUTHOR

78       Brendan Gregg, adapted for bpftrace by Dale Hamel
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