I am trying to use the tcpdump command in a project and I have some difficulties understanding the help page.
SYNOPSIS tcpdump [ -AbdDefhgHIJKlLnNoOpPqRStuUvxX ] [ -B buffer_size ] [ -c count ] [ -C file_size ] [ -G rotate_seconds ] [ -F file ] [ -i interface ] [ -j tstamp_type ] [ -k (metadata_arg) ] [ -m module ] [ -M secret ] [ -r file ] [ -s snaplen ] [ -T type ] [ -w file ] [ -W filecount ] [ -E spi@ipaddr algo:secret,... ] [ -y datalinktype ] [ -z postrotate-command ] [ -Z user ] [ -Q packet-metadata-filter ] [ expression ]
First, what is this "[ -AbdDefhgHIJKlLnNoOpPqRStuUvxX ]" at the top ? What is the meaning of that ?
I also see a lot of people on the internet doing crazy things with this command, for example
tcpdmp -nnvvXSs 1514 ... what is that -nnvvXSs, and how can we know this can be used ?
I see codes examples that according to me does not correspond to the man page, I just don't get how to read, how to understand this help file.
Anybody tell me how to read this and understand it ?