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Linux Printing HOWTO
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4.2. The parport device (kernels >= 2.1.33)

4.2. The parport device (kernels >= 2.1.33)

Beginning with kernel 2.1.33 (and available as a patch for kernel 2.0.30), the lp device is merely a client of the new parport device. The addition of the parport device corrects a number of the problems that plague the old lp device driver - it can share the port with other drivers, it dynamically assigns available parallel ports to device numbers rather than enforcing a fixed correspondence between I/O addresses and port numbers, and so forth.

The advent of the parport device has enabled a whole flock of new parallel-port drivers for things like Zip drives, Backpack CD-ROMs and disks, and so forth. Some of these are also available in versions for 2.0 kernels; look around on the web.

The main difference that you will notice, so far as printing goes, is that parport-based kernels dynamically assign lp devices to parallel ports. So what was lp1 under Linux 2.0 may well be lp0 under Linux 2.2. Be sure to check this if you upgrade from an lp-driver kernel to a parport-driver kernel.

The most popular problems with this device seems to stem from misconfiguration:

The Distribution

Some GNU/Linux distributions don't ship with a properly setup /etc/modules.conf (or /etc/conf.modules), so the driver isn't loaded properly when you need it to be. With a recent modutils, the proper magical lines from modules.conf seem to be:
alias /dev/printers lp             # only for devfs?
alias /dev/lp*      lp             # only for devfs?
alias parport_lowlevel parport_pc  # missing in Red Hat 6.0-6.1


Many PC BIOSes will make the parallel port into a Plug-and-Play device. This just adds needless complexity to a perfectly simple device that is nearly always present; turn off the PnP setting for your parallel port ("LPT1" in many BIOSes) if your parallel port isn't detected by the Linux driver. The correct setting is often called "legacy", "ISA", or "0x378", but probably not "disabled".

You can also read the parport documentation in your kernel sources, or look at the parport web site.

Linux Printing HOWTO
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  Published under the terms of the GNU General Public License Design by Interspire