Best of Technical Support

Our experts answer your technical questions.
Managing Modules

When I build a kernel (2.0.26 is the latest) with loadable module support enabled, I have troubles with the old modules compiled for 2.0.0. When I make the modules for 2.0.26, only one module is built and put under /lib/modules/2.0.26. How do I manage the other modules? When I put the 2.0.0 modules under 2.0.26, the system complains you must recompile. How do I recompile them? —Ivo Naninck

Patch or Scratch?

You did not mention whether you have applied a patch or installed a linux-2.0.26.tar.gz. If you have installed from scratch, don't forget to run make menuconfig, in order to select which features you want as modules. If you have applied a patch, use:

make dep
make clean
make zImage<\n>
make modules
make modules_install

I would prefer using make zlilo rather than make zImage, but the latter would work. This should compile your kernel and all the modules you have specified. Once the kernel is installed, you should be able to take care of dependencies with the command depmod -a the next time you boot. —Mario de Mello Bittencourt NetoWebSlave System Administrator

Making Rescue Disks

I am wondering if there is a guide on how to make a rescue disk that includes my choice of kernel and root, including some basic tools to help me restore my box in case of an accident. —Eskinder Mesfin

Bootdisk HOWTO

The Linux Bootdisk HOWTO by Graham Chapman ( describes how to create maintenance disks. The text is available at and —Martin Michlmayer

Linux Won't Accept Mask

We have a complex 10B2 network with 4 subnets. We recently got connected to the Internet with ISDN and a Pipeline 50 and were given a single class C address. We have created a subnet scheme for assigning IPs to all of our WFW3.11, Win95, and WinNT computers. When we tried to set up the Linux box as an HTTP and ftp server, we were unable to get the Linux software to accept as the subnet mask. Will Linux do subnets this way? —Richard C. Guglomo

Linux And Subnets

Linux does do subnets, and 224 is a valid mask. Valid masks must have contiguous high bits set and 224 is 1110 0000 in binary. In theory this should work, but there are some pitfalls.

It could be that the IP you are assigning to the interface isn't on a valid 224 subnet. With that mask your network addresses will be 5 bits. In other words, subnets will fall on multiples of 32 (decimal)—0, 32, 64. Those IP addresses are “network addresses” and can't be used for an interface. Similarly, the “all ones” addresses are reserved for broadcast—that would be 31, 63, and so on in this case.

You cannot assign a network address as the IP for a specific interface. So, you can't use something like as the interface address. Instead you should use 33-62 for the devices on the 32 subnet (63 would be the broadcast address and is also reserved), 65-95 for the 62 subnet, and so on. —Bob Hauck, Wasatch Communications Group

Can't Disable LILO

I have installed Red Hat, and I now want the option of running another OS on my machine, but I have not been able to disable LILO. I have installed DOS, but when the machine re-boots, I get LILO, and when I press TAB, I have no other options. I have fdisked the hard drive through both the Red Hat install program and DOS without any luck. I wanted to move the LILO from the mbr but have not been able to do this. —Josef Davis

Adding DOS option to LILO

You can replace LILO with the DOS boot loader by issuing the DOS command fdisk /mbr. In your case, however, the solution is to add DOS as an option to LILO. You can do this by adding the following directive at the end of the LILO configuration file, /etc/lilo.conf:

other = /dev/sda4
label = DOS
table = /dev/sda

You have to replace the value of other with the device of your DOS partition; the same applies to table where you have to insert the device of your hard disk (/dev/hda in the case of the first IDE hard disk).

After inserting these lines you have to refresh the boot record by issuing /sbin/lilo as root. When booting your machine the next time, you will have the option DOS within LILO. —Martin Michlmayer