设置tcpdump -W 1 -C 10时捕获文件的行为咨询

Let's break down exactly what this command does, compared to your original -W 5 example:

• Initial setup: When you start the command, tcpdump will create (or overwrite if it already exists) a file named capfile0 (note the trailing 0—tcpdump uses zero-indexed numbering for loop buffer files).
• Size threshold trigger: As tcpdump captures packets, it writes them to capfile0. Once this file reaches 10,000,000 bytes (10MB) (the -C 10 setting, where -C uses units of 1,000,000 bytes), instead of creating a new file like it does when -W 5 is set, it will:
  1. Close the current capfile0
  2. Truncate and overwrite the existing capfile0 (erasing all previous captured data in the file)
  3. Reopen the file and start writing new packet data to it
• Continuous cycle: This overwrite process will repeat every time capfile0 hits the 10MB limit. You'll never get more than one capture file, and it will always contain the most recent 10MB of captured traffic.

The key difference from -W 5 is that with -W 1, there's no rotation to new files—tcpdump just keeps replacing the single allowed file with fresh data once it hits the size cap.

内容的提问来源于stack exchange，提问作者Jialiang Zhou