Quickly Setting Up PLIP and NFS

Need to transfer files between your desktop and your laptop? Here's the easy way to do it by networking.

If you have two computers running Linux, one of which is a notebook, you are most likely tired of exchanging data between them using floppy disks. This article explains how to quickly set up these two computers so that you can use networking instead. Don't be afraid if you have no prior knowledge of networking; just follow the instructions step by step. If you have successfully installed Linux by yourself on your computer, you will be able to do this as well.

I'll start by setting up a PLIP (Parallel Line Internet Protocol) connection, which is simply a network connection through the parallel port. This port is most often used to connect a printer, and it is most probably located at the back of your computer. It has a connector with 25 holes. You will need a special cable to make this connection. Once made, you will have a full network connection allowing you to use ftp or rcp to transfer files between the computers.

Next, I'll discuss using NFS and mounting the disk of the notebook computer on the desktop computer. In this way, the disk of the notebook computer will appear as if it were a local disk on your desktop computer, and you can manipulate (edit, copy, etc.) your notebook files using your favorite commands.

Finally, I will show you how to access the Internet through PLIP from the notebook computer if your desktop computer has Internet access.

Assumptions and Conventions

I am using the Slackware 3.2 distribution of Linux (kernel 2.0.27), so if you have another distribution, some interpolation may be necessary—in particular, for the kernel configuration and the location of the system files. You will need the following:

  • two computers with Slackware 3.2—generic Slackware kernel—or your favorite Linux distribution

  • root access on both computers

  • your own account on both computers (with same UID for NFS)

  • TCP/IP package installed

  • parallel port plip1 on each computer (IO 0x378, IRQ 7)

I will use the following conventions for commands:

  • commands with prompt ending in # are issued as root

  • commands with prompt ending in > are issued as an unprivileged user

Finally, when editing files as root, remember to always make a backup copy of all configuration files before you alter them during the configuration process!

Part 1. What is PLIP?

PLIP is similar to SLIP (Serial Line Internet Protocol), except that it uses a parallel cable for the connection. SLIP is used for networking over serial lines (like modems, or the serial ports of your computer, usually with 9-hole connectors). Your printer and the PLIP connection cannot both be used at the same time, since they both use the parallel port. However, our primary goal is to have a temporary connection between the two computers, and switching between the printer and the connection is quite easy. You will have to connect/disconnect the cable manually, which may involve crawling under your desk. If you do this often, you may wish to consider buying a data switch box.

Setting Up PLIP

As already mentioned, the first thing you need is a “null-printer” parallel cable, which is often sold under the name “Laplink” cable or “PC-to-PC” cable. It is cheap (about $10 US) and easy to find in any computer store. There are also instructions on how to build one yourself in the NET-2-HOWTO, but I don't think it is worth the trouble and you could end up damaging your parallel port if you make a mistake—so just buy one.

Check the Kernel

Next, check your kernel. If you are using the distribution kernel that came with your Slackware 3.2 distribution, then you're all set. (If you don't know which kernel you are using, then you probably just have the generic one.) If not, check that you have loadable module support, networking support, PLIP and printer support as a module (no built-in printer support). If you have to recompile the kernel, then check the appropriate documentation and make sure to turn on these options:

CONFIG_MODULES=y
CONFIG_NET=y
CONFIG_INET=y
CONFIG_NETDEVICES=y
CONFIG_PLIP=m
CONFIG_PRINTER=m

Recompiling the kernel is not hard. You need to know what hardware you have and understand what all the options mean. Check the Kernel-HOWTO and the Documentation/Config.help file that comes with the kernel sources. If you have to recompile the kernel, first read this entire article, because later I will mention some additional options you may want to turn on.

With the correct options for the kernel, start the configuration, taking the following steps (as described in the next two sections):

  • Check for modules in /etc/rc.d/rc.modules and update /etc/hosts.

  • Write scripts to start/stop the connection.

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