Hack 7 Use Advanced Knoppix Cheat Codes

Choose advanced options for system tweaking and booting on exotic systems.

Knoppix's cheat codes let you change many of its default behaviors from which desktop environment to use to whether or not to eject the CD at shutdown. While many of the cheat codes have been merely enhancements to the defaults, there is also a full set of advanced options. Many of these advanced cheat codes can help you work around bugs in your hardware or in Linux's support of your hardware, or disable default options that could prevent Knoppix from booting. Some of the more advanced cheat codes for Knoppix are listed here:

Cheat code	Purpose
knoppix26	Boot with the 2.6 Linux kernel
knoppix atapicd	Do not use SCSI emulation for IDE CD-ROMs
knoppix alsa (or alsa=es1938 )	Use ALSA sound driver
knoppix no{acpi,apic,agp,apm,audio,ddc, firewire,isapnpbios,pcmcia,scsi,swap,usb}	Skip parts of hardware detection
failsafe	Boot with (almost) no hardware detection
knoppix pci=bios	Workaround for bad PCI controllers
knoppix mem=128M	Specify memory size in megabytes
knoppix dma	Enable DMA for all IDE drives

1.8.1 Kernel 2.6

The first advanced cheat code to mention, the ability to boot with the 2.6 kernel, is new with Knoppix 3.4. The 2.6 kernel has speed enhancements for desktop users, more features, and, in some cases, better hardware support, specifically for ACPI, which can be important for laptop users. If you are having trouble with your hardware with the default 2.4 kernel, 2.6 kernel might give you better results.

By default, Knoppix loads a kernel from the 2.4 series. To boot into 2.6 at the boot: prompt, type:

knoppix26 

One new feature of the 2.6 Linux kernel is the ability to write CDs from IDE CD-ROM drives without having to use SCSI emulation (the ide-scsi module). By default, Knoppix loads all of your CD-ROM drives with SCSI emulation so that you can easily use the included CD-burning software out of the box. If you are using the 2.6 kernel and want to disable SCSI emulation for all of your IDE CD-ROM drives, use the atapicd cheat code. This lets you burn CDs while accessing the IDE CD-ROM directly.

1.8.2 Use ALSA

Sound cards have traditionally been a problematic piece of hardware for Linux systems. Some cards don't have a driver, or the driver only addresses a part of the features that card supports. Knoppix's excellent hardware detection has eliminated much of the work in finding the proper driver for a sound card, but it defaults to using OSS (Open Sound System) drivers, because, in many cases, OSS drivers have proven to be more stable than the newer Advanced Linux Sound Architecture (ALSA) drivers.

If you need the extra features that ALSA provides, or your sound card works only through ALSA, tell Knoppix to use ALSA drivers instead of OSS by using the alsa cheat code. The alsa cheat code without arguments probes for the desired driver, or you can pass the driver as an argument. You can look up the ALSA module corresponding to your sound card on ALSA's sound card matrix at http://alsa-project.org/alsa-doc/. Input the manufacturer of your sound card into the form to receive links to pages for each chipset from that vendor. For instance, the Vortex 2 card uses the snd_au8830 ALSA module, so for Knoppix to use that module, type:

alsa=au8830

1.8.3 Solve Knoppix Booting Problems

Sometimes you might need to skip parts or full sections of Knoppix's hardware detection so that it boots on a system. On some hardware, certain parts of Knoppix's hardware detection have been known to freeze a system. On other systems, you might want to disable certain pieces of hardware you know are unstable. Knoppix allows you to use all of the standard Linux kernel parameters to disable as much of the hardware as you want. To disable a particular part of the hardware, just type no followed by the type of hardware to disable, such as noaudio to disable sound card detection. If you aren't sure which phase of hardware detection is failing, the expert mode [Hack #9] walks you through each phase step by step so you can see how far along Knoppix gets before running into trouble.

The complete list of kernel parameters is listed along with every kernel's documentation in the Documentation/kernel-parameters.txt file, which can be found at /usr/src/linux/Documentation/kernel-parameters.txt on the Knoppix CD.

There are many different kernel parameters you can use to disable hardware, but a few of these are well-known for booting Linux on problematic machines. A commonly suggested fix for many Linux boot problems is to disable APIC support, which can be done with the noapic cheat code. Disable power management with noapm or acpi=off to help stabilize systems with buggy power management. Pass pci=bios to the kernel to work around problems with bad PCI controllers. Experiment with disabling different options or multiple options at once, as sometimes it is more than one piece of hardware that prevents Linux from booting. If all else fails, boot with failsafe to disable almost all of the hardware detection. The failsafe mode serves as a good sanity check to see if the Knoppix hardware detection is even the problem.

1.8.4 Enable Hardware

Knoppix by default makes heavy use of ramdisks for temporary file storage while it is booted. Because of this, it is important that Knoppix actually detects all of your available RAM; otherwise, you might not be able to start X or load many programs once X is started. Some BIOSes have been known to be problematic and fail to accurately report the available RAM to Linux, but you can bypass these problems and tell Linux how much RAM is in the system by using the mem boot parameter. For example, if Knoppix isn't detecting all 256 MB of your RAM, tell the Linux kernel to use 256 MB of RAM, despite what the BIOS might claim, by typing:

mem=256M

Linux typically detects the proper DMA settings for any IDE devices in your system, and Knoppix enables DMA by default. DMA on hard drives gives a noticeable performance boost, and on DVD drives, DMA prevents movies from skipping. Sometimes you must force Knoppix to enable DMA on devices that you know support it. Use the dma boot parameter to enable DMA.

As you can see, there are many advanced cheat codes to pass to Knoppix at boot time. To get Knoppix to boot on a difficult system, the best combination of cheat codes depends heavily on the hardware involved. Hardware forums and newsgroups are great resources to search when trying to get Linux working with a particular chipset. Often other people have already done much of the guesswork for you. Pay particular attention to threads involving Linux installation even if the thread isn't about Knoppix, as those threads often list kernel parameters that work around or fix problematic hardware.