Send program's serial output to pseudo-terminal used by serial sniffer such as jpnevulator [duplicate]

Question

1. I am running an application that communicates through a real serial port e.g. /dev/ttyS0 to a remote device. I can configure this application to use /dev/ttyS0, /dev/ttyS1, etc., by passing the numeric suffix to the program, not the fully-qualified name.

2. I would like to sniff the traffic going through this serial port using something like jpnevulator. This jpnevulator opens a pseudo-terminal to which the application to be monitored is supposed to connect.

Is there any way to re-assign the name of the ports, for example /dev/ttyS1 to an actual pseudo-terminal such as /dev/pty/23, so that the application transparently connects to /dev/pty/23 via /dev/ttyS1? Would a file link ln achieve this?

Answer 1

If I were you, I would just edit the binary and replace the /dev/ttyS%d or similar string with /dev/ptyX%d (taking care that the replacement have the same length as the original), then create a symlink /dev/ptyX0 to the path of the slave end of the pseudo-terminal.

There are a lot of other solutions, more or less awkward:

a) if your system is linux, temporarily mount --bind /dev/pts/<pty used by the sniffer> /dev/ttyS2 (and connect your program to the serial line 2)

b) similarly, move /dev/ttyS2 out of the way and replace it with a link to the pty

c) run it inside qemu and redirect the serial port of the vm to the pty

d) some fake paths/filesystem solution using LD_PRELOAD

e) namespaces, unionfs, chroots, etc