Best of Technical Support

Our experts answer your technical questions.
Modem Compatibility

Can I use an internal PCI modem with Linux? I have been looking all over the web and have found no documents about this. —Luis David Cardenas,

The answer will depend upon which kind of modem you have (Plug-n-Play, winmodem etc.). If your modem has these switches (also called jumpers), configure it to use an IRQ/Com (IRQ3, Com 2 for example) and simply create a link (as root) to it:

cd /dev
ls -s /dev/cuaX /dev/modem

where the X is directly related to the Com port you have chosen (Com1 = cua0, Com2 = cua1 and so on). If your modem is Plug-n-Play, you will have to create an /etc/isapnp.conf file and configure it accordingly. —Mario Bittencourt,

Internet Connection Broken

I recently upgraded from Red Hat 5.1 to 5.2 and was surprised to see that my Internet connection no longer works. I set up my PPP connection through Network Configurator. I have no problem dialing and logging in, but when I pinged one of the sites, e.g.,, I got this message:

ping: unknown host

Which is strange, because it used to work under 5.1. —Genesis Elliott,

I suppose your ping is just a test and other things that used to work also stopped working (I am saying that because DNS might not be working, or the host you are pinging could have disappeared—I have seen that happen). Let's suppose your problem is truly linked to the upgrade. Make sure that /etc/resolv.conf still has correct values (netstat -nr; ifconfig), or else make sure you cannot ping hosts by their IP addresses (rather than host name). Then, if that fails, under interfaces/ppp/communication check the debug box, and do a tail -f /var/log/messages. Bring the connection up, and the messages from syslog in /var/log/messages should give you a clue as to what is wrong. —Marc Merlin

Chinese Big-5 Display

How do I display a Chinese charactered document under xterm and web browser? —Chi-Chih Chen,

You can use cxterm to display Kanji under Linux, and it offers several ways to input Chinese. Netscape can also be configured to display Mandarin in the View/Encoding menu, both simplified Big5 encoded Kanji and traditional Kanji as used in Taiwan.

You should read the Chinese Linux HOWTO at (it has a link to cxterm). —Marc Merlin,

Options at Compile Time

I know how to compile a new kernel and pick support for various options. Is there a way to do a sort of reverse lookup to find out which options were picked at compile time? This is needed in order to determine which options were compiled into a particular kernel I have floating around but for which I don't have the accompanying config file. —Ian Gilchrist,

This information is not saved as any type of text data specifically, but if you are creative you can find other ways to get this information. Each time Linux is compiled, a map file is also created. It contains the function names in the kernel, and with some work, you can probably figure out from there what you need to know.

It is a good idea to save the .config file with each compiled kernel. It has all the information you need; I often compress it with gzip and save it in the directory where I store my kernels. This is much handier than you may think. There is nothing worse than trying to compile a kernel for a two-year-old system with a really old LAN or SCSI card, when you cannot remember how you got it to work the first time. —Chad Robinson,

Accessing Home Pages via FTP

We are a small ISP and have used Windows NT, WebTEN and MachTEN for our services. We have now changed to Linux.

We have set up Linux, and we want our customers to be able to use ftp to put their home pages on the server. This works fine, but they also are able to go up the tree to see the /home/dir, and even more, the whole hard drive. I want to change it so that they can go into their /home/$USER and no further. I have tried to use the guestgroup option in /etc/ftpaccess to no avail.

How do I do it? What is the proper syntax? Can anyone send me a working line out of the /etc/ftpaccess and the /etc/passwd file? —A.H.J. Mittendorff,

The easier way is to create an FTP group (let's call it ftponly) in /etc/group and change your creation script to add the users with this group. Then edit your /etc/ftpaccess and add guestgroup ftponly. Now, if you try to log on using ftp, you should be able to see only your directory. Note that since FTP will chroot to the user's directory, you will also have to add a /bin directory with a statically linked ls version.

Also, check that your /etc/ined.conf has a line like this:

ftp stream tcp nowait root /usr/sbin/tcpd in.ftpd -l -a

—Mario Bittencourt,