• A kernel compiled with APM support. Redhat 5.2 and previous do not have APM support built into the stock kernels by default. Redhat 6.0 does, but the APM driver's interrupt handling is not configured appropriately for newer ThinkPads (although it should work form most laptops). Therefore, you will need to compile your own kernel with properly-configured APM support.

• Optional: The APM Daemon . APMD is a set of programs that controls the Advanced Power Management system found in most modern laptop computers. It communicates with the kernel APM driver, above. This package is included with Redhat Linux and is probably installed already. If not, install it using RPM. If you don't know how to use RPM, this reference guide ought to help.

• Optional: APM monitors. APM-aware battery monitors are available for various window managers and desktop environments like WindowMaker/GNOME and KDE. As an example, an iconized application like wmapm is designed to live in WindowMaker's Dock:

  

• Step 1: Grab the latest kernel source code from www.kernel.org -- or rather, please use one of its mirrors. I will use kernel 2.2.13 for my examples.

• Step 2: Log in as root. Then cd /usr/src. I usually remove or rename the existing linux subdirectory there. Then unarchive the linux source tree:
  • If it's in .bz2 format: bunzip2 -c linux-2.2.13.tar.bz2 | tar xvf -
  • If it's in .gz format: tar xvzf linux-2.2.13.tar.gz

• Step 3: Now cd /usr/src/linux. I recommend that you perform the kernel configuration in X-Windows. Type make xconfig. Shortly, a kernel configuration window will pop up:
  

• Start at the top left -- each window will lead you to the next window, and there is help for each option. The missing Allow Interrupts During APM BIOS calls option for proper APM support in newer Thinkpads is shown here, under General Options:
  

• Here's some help! In case you aren't already an experienced kernel-compiler, I've included my kernel configuration file for kernel 2.2.13 here. Just select the "Load Configuration from File" option, load the file ("gromit-2.2.13"; gromit's the name of my laptop) browse my options (altering to suit), and then hit "Save and Exit". I provide this file "as-is". If I left out a kernel option you like or need, it's not my problem.

• Step 4: All done? OK, click on Save and Exit. Now type make dep, then make clean, then make zImage, then make modules, then make modules_install. If you like, you can type these all on one line, each separated by a semicolon (;). In 5 minutes, it will be done (or your next kernel's free).

• Step 5: Your new kernel is in /usr/src/linux/arch/i386/boot/zImage. So let's copy it to the /boot directory where all the boot files live. Type:

  cp /usr/src/linux/arch/i386/boot/zImage /boot/vmlinuz-2.2.13

  Do the same for the new System map:
  cp /usr/src/linux/System.map /boot/System.map-2.2.13
  

• Optional: Create symlinks that point to these two files.

  rm System.map; ln -s System.map-2.2.13 System.map
  rm vmlinuz; ln -s vmlinuz-2.2.13 vmlinuz

• Step 6: Edit /etc/lilo.conf to reflect the new kernel you want to boot. My lilo.conf file alternately boots between my 2.2.13 kernel (boot label = linux) and the stock 2.2.5 kernel installed by Redhat 6.0 (boot label = backup):

        boot=/dev/hda
        map=/boot/map
        install=/boot/boot.b
        prompt
        timeout=100
        image=/boot/vmlinuz-2.2.13
            label=linux
        	  root=/dev/hda2
            read-only
        image=/boot/vmlinuz-2.2.5-15
  	  label=backup
  	  root=/dev/hda2
  	  read-only
        

• Step 7: Type /sbin/lilo to install lilo (the LInux LOader) with knowledge of your new kernel. Don't forget this! :) Now go ahead and reboot. If you did everything correctly, you'll have a nice new optimized kernel with functional APM support and much more. If not, go ahead and reboot with the old stock kernel...

• To conserve disk space, you may want to go back into /usr/src/linux and type make clean; make mrproper to clean up the source tree. This will save substantial (tens of MB) disk space. You can remove the source tree if you don't need to recompile the kernel, but definitely leave the /usr/src/include directory intact if you do any kind of development work.

  Note: You will want to rebuild PCMCIA Card Services for the new kernel, so DON'T remove the kernel tree until you have rebuilt PCMCIA.

The above sounds involved, and it is (albeit instructive)! But being able to use the suspend and resume features of your laptop is very cool indeed. You can work weeks, months without ever rebooting your computer! And your work is always right where you left it. :) I recommend it highly.

A few notes on using APM:

• Once APM kicks in, upon the first suspend and resume, the CPU will be running in power-saving mode and at a somewhat reduced clock rate. This appears to be independent of any BIOS settings. I suspect that this behavior is not seen if you disable the Make CPU idle calls when idle compilation switch in the APM portion of kernel configuration. If you are running serious numerical processing and need every cycle, you may wish to disable CPU idling, or not suspend the processor.

• An alternative to suspend-resume is standby mode, invoked by Fn-F3 instead of Fn-F4 (suspend). This turns off the LCD backlight and dramatically improves battery life. You can also use apm, the BIOS, or hdparm to spin down the EIDE hard disk after a specified amount of time.

• Hibernation mode (Fn-F12, writing RAM to disk and shutting completely down) does not work in non-Windows OS's according to IBM. However, there appears to be a hack in Linux to make it work... the link is provided on the APMD page.

• If you suspend from X-Windows, on occasion the screen will come up garbled on resume. Just hit Ctrl-Alt-F1 to get to a virtual console and flip back again; X-Windows just needed a signal to redraw the screen. :) If this becomes a problem, flip to a virtual console before suspending your computer.

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