On Fri 15 Sep 2017 at 16:29:32 +0200, Michael van Elst wrote:
> On Fri, Sep 15, 2017 at 05:52:10AM -0400, William D. Jones wrote:
> > * I wanted to use the serial port that defaults to the console on my rpi as
> > the ppp connection for various logistical reasons. Can I redirect kernel
> > messages (and init messages) to another tty without recompiling? I don't see
> > a kernel option in `man boot`.
>
> The kernel messages always go to the "console", which is a low-level
> interface. The kernel only knows two such devices (or three since a few
> days), which are the serial port, the framebuffer/keyboard and the
> second serial port (for RPI3 support).
Look at tty(4), TIOCCONS:
TIOCCONS int *on
If on points to a non-zero integer, redirect kernel console
output (kernel printf's) to this terminal. If on points to a
zero integer, redirect kernel console output back to the
normal console. This is usually used on workstations to
redirect kernel messages to a particular window.
> Once the kernel is running, the console can be intercepted by a program.
> In standard X11 there is a xconsole doing this, which displays the
> messages in a window.
I suspect that xconsole does this by opening a pty and issuing TIOCCONS
on it.
Screen can also issue TIOCCONS:
console [on|off]
Grabs or un-grabs the machines console output to a window. Note: Only
the owner of /dev/console can grab the console output. This command is
only available if the machine supports the ioctl TIOCCONS.
Apart from that, a simple program to issue the ioctl on stdout is easily
written.
-Olaf.
--
___ Olaf 'Rhialto' Seibert -- Wayland: Those who don't understand X
\X/ rhialto/at/falu.nl -- are condemned to reinvent it. Poorly.
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