Write to the stdin of a running process with the same effect/behaviour of directly writing

Geo asked:

This post answers only partial my question. My problem is that writing to the stdin of the running process using the FD of process on the /proc filesystem does not have the same effect.


  1. start nc to listen on port 10000 (this process is called further nc 1)

    nc -l 10000
  2. start another nc to send chars to the listening nc (this will be nc 2)

    nc localhost 10000
  3. Write to the stdin on the nc 2

    echo "some chars here" >> /proc/[PID-nc-2]/fd/0

the problem: “some chars here” do not get to the listening nc (nc 1), BUT are shown on the console of the nc 2.

why and is it possible to make this working?

My answer:

As stated in the answer to the post you linked, you need to write to /proc/pid/fd/0, not /proc/pid/fd/1.

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