go-将stderr重定向到文件AND到stdout

I would like to redirect stderrto a file AND to stdout.

I know how redirect stderr to file using dup2 :
err := syscall.Dup2(int(fatal_logfile.Fd()), int(os.Stderr.Fd()))

But then I don't see how can redirect this another time to stdout. Like "copying" one stream-source to two differents streams.

Just a note, this functionality is called when the app starts and used to redirect stderr when, for example, a panic occurs. Then I cannot use recover in this case (even because I am running lots of goroutines).

Anyone has an idea how to solve this?

Another working solution is to use pipes and tee when calling the binary, but is possible to have the same behavior/logic defined inside the app? I would like that it runs in this way as default.

./app_bin 2> >(tee -a fatal.log)

writer := io.MultiWriter(os.Stdout, os.Stderr)

Whatever it's written to writer will write to os.Stdout and os.Stderr.