Re: Fork and Exec a process within the kernel

[Erik Mouw <erik@harddisk-recovery.com>]

On Wed, Aug 11, 2004 at 07:55:52AM -0400, Richard B. Johnson wrote:
> RedHat is NOT Linux. The MAJOR-MINOR 5.1 used in RedHat for the
> console has a very serious problem for anybody doing development
> work. If there are any kernel messages, they go to __all__ open
> terminals. This means that the only "quiet" terminals that may be
> available to kill off a runaway process are available iff you can
> log in over the network.

If you don't want console messages, you just disable console at all, or
you use a serial console (using the "console=" on the kernel command
line), or you adjust the kernel console log level. Please have a look
at the "dmesg" manual page, especially the "-n" parameter. In emergency
situations, Alt-Sysrq-[0-8] will allow you to do the same (on VGA
consoles for PCs, that is. for serial consoles use Break-[0-8]).

> Most everybody I know, who does serious development work, and
> certainly those who want to control where the %*)&$#!@ kernel
> messages go, will make sure they go to the "ALT-F1" as I have
> shown.

Not all the world is a PC, there is a lot of linux beyond x86. Looks to
me like you haven't done development on embedded systems that don't
have any VGA terminal at all.

Getting kernel messages on a certain pseudo tty is just a matter of
supplying the correct "console=" paramater to the kernel. For example:
"console=tty1" will get your console output on pseudo tty 1.
Alternatively, you can configure syslog to write all kernel messages to
a pseudo tty.

> The original query was about how to make kernel messages
> go to where, i.e., what VT do they come from. I have shown
> how you can control where they go.

Here is the original question:

  Thanks for the pointer! My user mode program is running. Any idea how to
  control which console it shows up on?

No reference on how to get kernel messages somewhere.

> Now, if you look at the kernel source, you will note that
> just prior to attempting to exec /sbin/init, /dev/console
> is opened. This means that you can properly use whatever
> you want if you continue to use a sym-link.

That was true for linux < 2.1.71, which was released almost 7 years
ago. Things have changed. Newer kernels use the "console=" kernel
command line to select the console. With multiple the "console="
parameter, you can even have mutiple consoles.


Erik

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