Best of Technical Support

Our experts answer your technical questions.
Dependencies and Libraries

Recently, I downloaded a Linux application and when I tried installing it, I encountered an “unsatisfied dependencies” error message in the package manager. Where do you go for missing Linux libraries and how do you install them? —Kelvin L. Barnes,

If you're using an RPM-based distribution such as Red Hat, you install missing libraries the same way as any other software (i.e., by installing RPMs with the rpm program). You can find the RPMs containing these libraries by searching or On my Red Hat 6.1 box, I've installed the rpmfind utility (which was on the CD) provided by these sites, and it makes finding and downloading RPMs a snap:

rpmfind -v --auto --latest

You still have to install the RPMs (as root, typically) after they're downloaded:

rpm -Uhv
Another place to search is your distribution's download sites, which sometimes include software that wasn't shipped on the CD for various reasons. Red Hat's sites (use mirror sites if possible) are at and Occasionally, RPMs designed for one distribution may not operate correctly on another—the RPM itself is okay, but the files contained in it may have been configured differently, or they may be placed in different locations than normal for your distribution. If given a choice, choose an RPM that matches your distribution (e.g., if you're running Red Hat and you see “redhat” in the URL of one of the RPMs, that's probably the one you should choose). I have rarely encountered this problem, though. —Scott Maxwell, Was this “application” a RPM file? If so, it should have taken care of all dependencies. Otherwise, the “missing” libraries could be an infinite number, so reading the application's documentation, specifically about requirements, should point you in the right direction. Usually your distribution's web site should have all sources for your Linux libraries and you should be able to download almost (99%) everything from there, unless it is a very specialized library. —Felipe E. Barousse Boué,

One Working Parallel Port

I've installed two additional parallel ports on a PC, and I would like to use them all. So far, only /dev/lp0 works. Echoing into /dev/lp1 and /dev/lp2 returns the following nastygram:

BASH: /dev/<device name>: Device not configured

The ports work under Win98, so there are no IRQ or I/O address conflicts. Here's some more information:m

IRQ     IO range        Win98 name
7       0378-037f       lpt2
5       03bc-03be       lpt1
9       0278-027a       lpt3

—Luis F. Gonzalez,

Using ports in Linux requires two steps. First, your kernel must recognize the devices. You can check this by either scrolling through your boot messages by typing dmesg | less, or checking /proc/ioports and /proc/devices. The second step is to create the device file in /dev. If this file does not exist, you can use the makedev script found in the same directory to create most Linux device nodes. If it does exist, your problem is most likely with the first step. —Chad Robinson, If you've installed the kernel sources, the file /usr/src/linux/Documentation/parport.txt addresses this in detail. Briefly, if the ports are not automatically recognized and configured, and if printing and parallel port support are compiled as modules (not compiled into the kernel proper), try adding the following lines to the file /etc/conf.modules:

alias parport_lowlevel parport_pc
options parport_pc io=0x3bc,0x378,0x278 irq=5,7,9
options lp parport=auto

Then, from the shell, try removing and reinserting the relevant modules (the order is important):

rmmod lp
rmmod parport_probe
rmmod parport_pc
rmmod parport
insmod parport
insmod parport_pc
insmod parport_probe
insmod lp

You will need to do all of this as root. I'm not an expert at configuring parallel ports, since it normally works correctly out of the box for me; I've done it on only one machine, and on a different distribution from yours, so I may have overlooked something. You may need to experiment a little before it works. Perhaps some ambitious reader will turn parport.txt into a proper HOWTO, if that hasn't been done already. —Scott Maxwell,