Virtual Serial Port for Linux

You can use a pty ("pseudo-teletype", where a serial port is a "real teletype") for this. From one end, open /dev/ptyp5, and then attach your program to /dev/ttyp5; ttyp5 will act just like a serial port, but will send/receive everything it does via /dev/ptyp5.

If you really need it to talk to a file called /dev/ttys2, then simply move your old /dev/ttys2 out of the way and make a symlink from ptyp5 to ttys2.

Of course you can use some number other than ptyp5. Perhaps pick one with a high number to avoid duplicates, since all your login terminals will also be using ptys.

Wikipedia has more about ptys: http://en.wikipedia.org/wiki/Pseudo_terminal

Use socat for this:

For example:

socat PTY,link=/dev/ttyS10 PTY,link=/dev/ttyS11

Complementing the @slonik's answer.

You can test socat to create Virtual Serial Port doing the following procedure (tested on Ubuntu 12.04):

Open a terminal (let's call it Terminal 0) and execute it:

socat -d -d pty,raw,echo=0 pty,raw,echo=0

The code above returns:

2013/11/01 13:47:27 socat[2506] N PTY is /dev/pts/2
2013/11/01 13:47:27 socat[2506] N PTY is /dev/pts/3
2013/11/01 13:47:27 socat[2506] N starting data transfer loop with FDs [3,3] and [5,5]

Open another terminal and write (Terminal 1):

cat < /dev/pts/2

this command's port name can be changed according to the pc. it's depends on the previous output.

2013/11/01 13:47:27 socat[2506] N PTY is /dev/pts/**2**
2013/11/01 13:47:27 socat[2506] N PTY is /dev/pts/**3**
2013/11/01 13:47:27 socat[2506] N starting data transfer loop with FDs 

you should use the number available on highlighted area.

Open another terminal and write (Terminal 2):

echo "Test" > /dev/pts/3

Now back to Terminal 1 and you'll see the string "Test".