Use the tcpdump command to capture packets and save the result to a specified file, which can be achieved by specifying the output file parameter.
Here is an example command:
tcpdump -i <interface> -w <output_file.pcap>
where <interface>is the network interface to capture packets from, either the network interface name (for example eth0) or "any" (for all interfaces).
<output_file.pcap>is the name of the file to save the capture result, usually with an extension of .pcap. You can replace it with your desired filename and path.
For example, to capture packets on the eth0 interface and save the results to a "capture.pcap" file, the following command can be used:
tcpdump -i eth0 -w capture.pcap