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Editorial Team
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Asked: 2026-05-15T10:56:25+00:00

I write a program that send TCP packets from localhost to localhost. And I

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I write a program that send TCP packets from localhost to localhost. And I want to use tcpdump to capture the packets. But nothing is captured.
My command in Ubuntu:

sudo tcpdump

What argument shall I add? Thanks!

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1 Answer

  1. Editorial Team
    sudo tcpdump -i lo

    Notes

    • If you get tcpdump: lo: No such device exists, get the name by coping it from the output of
    sudo tcpdump -D

    For example, if the output is as below you need lo0 (which is reusult 9. here:

    1.en0 [Up, Running]
2.p2p0 [Up, Running]
3.awdl0 [Up, Running]
4.llw0 [Up, Running]
5.utun0 [Up, Running]
6.utun1 [Up, Running]
7.utun2 [Up, Running]
8.utun3 [Up, Running]
9.lo0 [Up, Running, Loopback]
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