How can I capture traffic continuously, with multiple interfaces on multiple nics?

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Captures on any will come in as Linux cooked-mode capture (SLL)

dumpcap, or tcpdump both support mutiple -i arguments to specify the interfaces to capture on.

dumpcap, yes; tcpdump, no. Tcpdump, confusingly, uses the argument to the last-i argument as the single interface on which to capture.

I was positive I'd checked the man page for tcpdump when writing the answer but I obviously imagined it.