Stdin and stdout redirection

Question

There is a statement

stty onlcr 0>&1

in rc.sysvinit file. What does exactly this line do? What's the reason for redirecting stdin to stdout?

Answer 1

$ man stty
...
   * [-]onlcr
          translate newline to carriage return-newline
...

and there's even a comment in the file, which you failed to mention:

# Set onlcr to avoid staircase effect.

So that should make it clear what the line does. stty operates on stdin by default, but this line changes output settings, so 0>&1 makes it work on stdout. Which can actually matter if you've a box where the console stdout is hooked up to one serial port, and the console stdin input to some other source ...

Edit

stty changes terminal parameters. To do so, it must issue system calls which operate on a file handle that correspond to a terminal. By default, this is stdin, as the manpage says:

  -F, --file=DEVICE
          open and use the specified DEVICE instead of stdin

I'm not sure what kind of example would help you ...

Answer 2

If you type man stty you'll get the documentation for stty, which among other things says

[-]onlcr translate newline to carriage return-newline

The reason for the redirection is that stty operates on its stdin, but there's only stdout available at the time the command is run.