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Re: switching between CUPS and PLIP?

ScruLoose said on Fri, Feb 28, 2003 at 03:04:04AM -0500:
> with a couple of questions.  Presumably, on my desktop box with its one
> parallel port, I'll need to unload lp before loading plip, so that plip can
> 'own' the parallel port.  
> Right?  

I've never actually used PLIP, but I'd imagine that's the safest way.

> And the way to do this is modprobe -r lp and then modprobe plip... yes?


> Is there some way I should be informing the rest of my system that I'm
> doing this (so that nothing starts attempting to print...)?

Nope.  If you're really worried about it, just take CUPS offline
(/etc/init.d/cupsys stop) for the duration.

> (Sorry, I'm still pretty new, and have little idea of how modules interact
> with the system.)

Modules are device drivers (more or less).  If a program attempts to use a
device that isn't loaded, the kernel will either automatically load it (using
modprobe), or it will return an error to the program, which will either handle
it or do something unexpected.

> Okay, so assuming I'm right so far: once I've got plip configured and the
> install is done, and I want to re-enable printing, I'll unload the plip
> module, and load lp back in.

Sounds about right.

> And further, after this is done, will it be basically a question of just
> modprobe-ing lp and away we go, or is this process going to wreak bloody
> havoc on my CUPS setup?  Is it reasonably easy to just switch back and
> forth between CUPS and PLIP?

Well, I'd probably just try it, but if you want to be paranoid:

/etc/init.d/cupsys stop
modprobe -r lp
modprobe plip
<do stuff with plip>
modprobe -r plip
modprobe lp
/etc/init.d/cupsys start

> Also, if anyone has any pointers to some good reading to help gain an
> understanding of modules... when, why, and how to load/unload them... how
> "regular executables" interact with them... what are dynamically loadable
> and which only load/unload with a reboot...

Check the kernel source documentation (apt-cache search kernel-doc... there's
one for each kernel varient... just install the one that matches the kernel
you're running).  It has documentation about modules.


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