Using Linux:Managing the Kernel






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Configuring the kernel


The details are the same
Most of the kernel configuration options are discussed in the previous section, and only the finer points are covered here.


1.  Start the configuration by clicking the Code Maturity Options button. This should always be your starting point when configuring a new kernel.
2.  It is generally safe to answer Y to Prompt for Development and/or Incomplete Code/Drivers, shown in Figure 32.7. For the most part, these changes to the kernel can enhance performance, and truly experimental code will be made obvious to you. To continue, click Next.

Figure 32.7  Selecting the Code Maturity Options.
3.  The next screen, Loadable Module Support, is shown in Figure 32.8. Answering Y to all three questions here is recommended for Red Hat Linux, unless you really have a lot of experience with this, or are experimenting to get that experience. Click Next to continue.

Figure 32.8  Configuring the loadable module options.
4.  The General Setup screen, shown in Figure 32.9, gets more interesting. Here you can choose to include support for kernel math emulation, processor type, and so on. Fresh kernel sources (ones that have not yet been configured on your system) have pretty safe defaults built in. The same caveats as in the make config section apply to everything here. Click Next to continue.

Figure 32.9  Configuring the general settings for the kernel.
5.  The next screen, shown in Figure 32.10, configures your floppy disks, IDE drives, and non-SCSI block devices. You will probably have noticed by now that the questions are almost, if not exactly, identical as the questions that make config poses, but appear in a graphical format. Help, of course, is much more accessible. Note that the scroll bars on the right of the screen allow you to see the rest of the configuration options. In this section you get to set up your IDE devices and drivers for them. Click Next to continue.

Figure 32.10  The scroll bars on the right of the block device configuration screen allow you to see the rest of the configuration options.
6.  Networking options are configured in the next screen, shown in Figure 32.11. These are covered in depth in the make config section above. Note that if you answer Yes to certain options, other sections become ungrayed. This makes it easy to determine which options must be enabled to allow you do what you want.

Figure 32.11  Configuring the network devices.
7.  The SCSI configuration screen is next (see Figure 32.12). Here you can choose to support various generic SCSI devices, and how to modularize the SCSI subsystem. Note how this kernel configuration is set up. The commonly used parts are compiled into the kernel (make sure you do this with SCSI Disk Support if you don’t want to fight with mkinitrd), and the less commonly used parts are compiled as modules.

Figure 32.12  The Basic SCSI configuration screen is shown. Note how the modules are selected.
8.  Click Next to bring up the SCSI Low-level Drivers section (see Figure 32.13). The advantage of the graphical configuration program here is that you can see which questions are coming for IO Addresses and so forth, before you get there. You can also go back and fix things easily if necessary. It’s worth noting that some of the tagged command queuing options and SCB paging options have a profound impact on the performance of the system, so be sure to read the driver documentation for your card.

Figure 32.13  The SCSI Low-level Drivers selection dialog box is shown.
Again, note that the stock system has your SCSI disk driver as a module if your system boots from it, and make sure that you disable the initial ramdisk if you decide to compile the driver directly into the kernel.
9.  The Network Device Support screen, which allows you to configure the network cards as well as SLIP and PPP connectivity for your machine, appears next (see Figure 32.14). Again, making PPP and SLIP modules is reasonable here, since kerneld knows about them and automatically loads them.

Figure 32.14  The Network Device Support screen probably lists the most devices, and can take some time to work though. Take your time.
10.  ISDN support is next (see Figure 32.15). Choose the device connected to your computer. If you cannot find your particular device, start looking in the help screens, as well, for documentation in the /usr/src/linux subdirectories for any to see if your ISDN modem is compatible with something.

Figure 32.15  ISDN configuration options. Note that when experimenting with any device you’re not sure of, it’s best to use the driver as a module so you don’t have to reboot every time you try different settings.
11.  The non-SCSI and non-IDE CD-ROM device support section is next (see Figure 32.16). There are fewer and fewer of these devices around, but your system may still have one. It’s particularly likely if your system has a double-spin drive, since most of these proprietary interfaces date back to that era.

Figure 32.16  The screen shot shows the CD-ROM configuration screen. Be prepared to give IRQ and IO Addresses for some CD-ROMs.
12.  In the Filesystems screen that appears (see Figure 32.17), pick your file systems and move on. I recommend making any file system you want modular, except for ext2fs, because your system will need to use that to mount its initial ramdisk and the root partition.

Figure 32.17  On the Filesystems configuration screen, make sure that you don’t disable the ext2 file system, or make it a module.

13.  Character Devices is where support for parallel ports, serial ports, and non-serial mice is configured (see Figure 32.18). If you plan to use a parallel port Zip drive, you’ll want to make your parallel port driver as well as your Zip driver modular; the Zip driver does not yet support sharing the parallel port.

Figure 32.18  The Character Devices screen.
14.  The sound card for your Linux system is now configured (see Figure 32.19). Everything noted in the make config section applies here, but also note that it is possible to hard-set non-standard device addresses for your sound modules using make xconfig. It’s worth noting that few of the configuration fields in this section check for “sane” values, so it’s up to you to make sure that you enter correct ones. Make the sound driver static (by answering Yes), then change the option Sound Card Support back to being a module. This has the effect of producing only one module to contain sound support, which is something I have had a lot less trouble with.

Figure 32.19  The Sound configuration screen.
15.  The last screen allows you to enable kernel profiling. Unless you’re doing some fine-tuning and development on the kernel (in which case this entire section should have put you to sleep), it’s of no use, and better left set to No. Click the Main Menu button to return to the main menu.
16.  Click the Save and Exit button, and you’re now ready to build your kernel.



Getting help
Note the Help buttons next to the options. By now, most options are well documented in the online help for the kernel. Feel free to use this facility as you see fit. I use it often, even if only to see whether things have changed between versions.



Modularizing drivers can be handy
It’s probably worthwhile to modularize your ISDN drivers if you’re experimenting. That way, device addresses and so on can be changed by unloading the module and reloading it with different parameters. It’s also possible then to recompile a module and use it without rebooting the system in most cases.





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