Hi Folks,

I'm trying to get a compiler and debugger going that uses the parallel port to communicate with the on chip debugger on a microprocessor. When I run the program it tells me:

"Cannot open target interface. Parallel port is already in use."

Is it possible to find out what Linux thinks is using the parallel port and then freeing it up?

I'm not using the parallel port for printing (in fact I'm doing all my printing over the network) and before I ran this program I didn't have a parallel port setup and had to run mknod for parport0...

I'm using Mandrake 9, btw...

Many thanks,

Rob.

Not sure it will work, but worth trying: as root or whatever your parallel port is called

Sadly, no. That doesn't list anything using it. Looked like the right command though did lsof!

Of course, there may well be nothing using it, but the software might be flaky!

Try making "ln -s /dev/parport0 /dev/par0" maybe the error description is misleading, and it can't just open the interface.

It happens to me in VMware if I have CUPS or a printer service setup. You can remove that module (I think lp) and try it again. You may want to set the parport to mode 666. Do not forget to load up lp module after you are done.

If you're using VMWare, then you may want to disable parallel port support the the client OS and use a share your printer as a network printer, and then use network printing (even though it's on the same machine). The problem, as I see it, is that both the host and the client OS are trying to access the parallel port and only one is allowed to do so. The answer: eliminate the problem.

Check to see if the 'lp' module is loaded with "lsmod" (as root), if it is then unload it with "rmmod lp".
'lp' is the pp printer module.

Aussie, you beaut, that's it! Thanks!

At the risk of sounding ignorant (not so far from the truth) - what am I doing there by entering rmmod lp? I guess I'm removing a "module" - whatever that is - for lp (line printer?). Is a module a piece of code that allows the kernel to interface with hardware?

Bear in mind that I'm a programmer, and I'm not stupid, but all my experience is low level code - assembler and C for microcontrollers...

Oh, btw thanks to the other suggestions I'm running Mandrake 9.1, not VMware.

Many thanks!

Rob.

Your welcome :-)

Yes, if Mandrake uses hotplug you can stop it loading the lp module at boot by adding it to /etc/hotplug/blacklist.

Yes, but thats not all a module can do, you can have filesystem support compiled as modules (but it's not a good idea to have your primary filesystem as a module) and iptables support is usually compiled as modules.

Have a look at file:/usr/src/linux/Documentation/modules.txt for more info on dynamically loadable kernel modules.

This problem has raised its ugly head again now I've installed Mandrake 10.

Initially I didn't have a parallel port listed at all, (and the application was telling me /dev/parport0 didn't exist) so I did:

modprobe parport_pc

which I saw recommended somewhere else here, but it seemed to do nothing, so I did:

modprobe parport

as well. This didn't quite work properly, it was still saying /dev/parport0 didn't exist, though the directory /dev/lp0 had suddenly appeared.

I did:

ln -s /dev/lp0 /dev/parport0

Which eventually stopped the message telling me /dev/partport0 didn't exist, but then told me:

"Can't open target interface, parallel port already in use"

So, I thought, no problem, I'll do:

rmmod lp

as I did last time. However, whenever I run the application, lp reappears in the lsmod listing.

I now have parport_pc, parport and lp0 in my lsmod. If I remove parport_pc, parport and lp an do lsmod, they all go. As soon as I try connecting to the parallel port with my application they all appear as below in lsmod

parport_pc 32832 1
lp 12200 0
parport 38952 2 parport_pc,lp


I seem to have got myself in a real tangle! Anyone have any ideas what I've done wrong?!

Many thanks.

Rob.

Sussed it, I needed to do mknod, not just make a symbolic link to parport0.

Sorreeeee!