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| linux:kernelbuilding [2009/02/21 21:54] – Update versions to match Slackware 12.2. More mkinitrd examples. Alternative way to let root run X programs. alien | linux:kernelbuilding [2009/07/22 07:20] – Fix a typo. alien |
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| ===== Building a Linux Kernel from source ===== | ===== Building a Linux Kernel from source ===== |
| ----------------------------------------------- | |
| |
| **This is a short recap of how I build my 2.6 kernels.** | **This is how I build my 2.6 kernels.** |
| |
| ==== X and su ==== | ==== X and su ==== |
| Now, get a Slackware kernel config file for a headstart during your own configuring. Pat's config files are pretty generic. By the time you read this, there might be a config for a newer 2.6 release available: | Now, get a Slackware kernel config file for a headstart during your own configuring. Pat's config files are pretty generic. By the time you read this, there might be a config for a newer 2.6 release available: |
| <code> | <code> |
| wget http://slackware/mirrors.tds.net/pub/slackware/slackware-12.2/source/k/config-generic-smp-2.6.27.7-smp | wget http://slackware.mirrors.tds.net/pub/slackware/slackware-12.2/source/k/config-generic-smp-2.6.27.7-smp |
| cp config-generic-smp-2.6.27.7-smp /usr/src/linux/.config | cp config-generic-smp-2.6.27.7-smp /usr/src/linux/.config |
| </code> Alternatively, you can grab the configuration for the kernel which is currently running: <code> | </code> Alternatively, you can grab the configuration for the kernel which is currently running: <code> |
| </code> | </code> |
| |
| You now have configured a pretty generic kernel (that is the reason why Pat calls them "kernel-generic" probably :-) but you will want to change some of the defaults to suit your needs. Run the X based configurator (if you do not run X but are at a text console, just run "make menuconfig" to get the curses-based dialog program instead) | You now have configured a pretty generic kernel (that is the reason why Pat calls them "kernel-generic" probably :-) but you will want to change some of the defaults to suit your needs. Run the X based configurator (if you do not run X but are at a text console, just run "''make menuconfig''" to get the curses-based dialog program instead) |
| <code> | <code> |
| make xconfig | make xconfig |
| Walk through the forest of options. What I usually change are things like: | Walk through the forest of options. What I usually change are things like: |
| |
| * build the ext3 (needs the jbd driver as well) and reiser/xfs/jfs fileystem drivers into the kernel instead of compiling them as modules - that way I do not need to create an additional "[[#creating_an_initrd|initrd]]"\\ (see under "Filesystems" in the configurator). | * Build the ext3 (needs the jbd driver as well) and reiser/xfs/jfs fileystem drivers into the kernel instead of compiling them as modules - that way I do not need to create an additional "[[#creating_an_initrd|initrd]]"\\ (see under "Filesystems" in the configurator). |
| |
| * enable 64GB of RAM.\\ (under "Processor type and features" > "High Memory Support (64GB)"). Use this if you have a system with 4GB of RAM or more. | * Enable 64GB of RAM.\\ (under "Processor type and features" > "High Memory Support (64GB)"). Use this if you have a system with 4GB of RAM or more. |
| |
| * enable the "low-latency" kernel if you run a desktop/laptop computer - multimedia apps will run much smoother\\ (under "Processor type and features" > "Preemption model" > "Preemptible kernel"). If you run a desktop system with a lot of multimedia applications, then this is an useful option for you because it will keep your system more responsive even under high load. | * Enable the "low-latency" kernel if you run a desktop/laptop computer - multimedia apps will run much smoother\\ (under "Processor type and features" > "Preemption model" > "Preemptible kernel"). If you run a desktop system with a lot of multimedia applications, then this is an useful option for you because it will keep your system more responsive even under high load. |
| |
| * set a 1000 Hz timer (under "Processor type and features" > "Timer Frequency" > "1000 Hz"). A higher tick count can be beneficial to multimedia 'desktop' systems. | * Set a 1000 Hz timer (under "Processor type and features" > "Timer Frequency" > "1000 Hz"). A higher tick count can be beneficial to multimedia 'desktop' systems. |
| |
| * or set a tickless timer (dynamic ticks - under "Processor type and features" > "Tickless System (Dynamic Ticks)"). | * Or set a tickless timer (dynamic ticks - under "Processor type and features" > "Tickless System (Dynamic Ticks)"). |
| |
| * ... and more I can't think of right now. You can decide to disable a lot of the modules that the default config will build, to cut down on time, if you don't have the hardware in your computer. You could also looka at software suspend and CPU frequency scaling (under "Processor type and features") if you own a laptop. | * If you are (re-)building a Slackware kernel, you should make sure that installing your new kernel will leave the original kernel modules intact. You do this by changing the //local-version// part of the kernel's release number to an unique string (under "General setup" > "Local version - append to kernel release"). This kernel option corresponds to **CONFIG_LOCALVERSION** in your ''.config'' file. Slackware sets that value to "-smp" for a SMP kernel to give you an idea. \\ The resulting kernel release value (as returned by "''umake -r''") for a kernel version "''2.6.27.7''" with a local-version of "''-alien''" would be "''2.6.27.7-alien''" |
| | |
| | * ... and more I can't think of right now. You can decide to disable a lot of the modules that the default config will build, to cut down on compilation time, if you don't have the hardware in your computer. You could also look at //software suspend// and //CPU frequency scaling// (under "Processor type and features") if you own a laptop. |
| |
| And finally save your configuration if you're satisfied. | And finally save your configuration if you're satisfied. |
| | |
| |
| ==== Building your kernel ==== | ==== Building your kernel ==== |
| make bzImage modules # compile the kernel and the modules | make bzImage modules # compile the kernel and the modules |
| make modules_install # installs the modules to /lib/modules/<kernelversion> | make modules_install # installs the modules to /lib/modules/<kernelversion> |
| cp arch/i386/boot/bzImage /boot/vmlinuz-custom-2.6.27.7 # copy the new kernel file | cp arch/x86/boot/bzImage /boot/vmlinuz-custom-2.6.27.7 # copy the new kernel file |
| cp System.map /boot/System.map-custom-2.6.27.7 # copy the System.map (optional) | cp System.map /boot/System.map-custom-2.6.27.7 # copy the System.map (optional) |
| cp .config /boot/config-custom-2.6.27.7 # backup copy of your kernel config | cp .config /boot/config-custom-2.6.27.7 # backup copy of your kernel config |
| </code> | </code> |
| |
| | With 2.6.x kernels, running "''make''" or "''make all''" instead of "''make bzImage modules''" should be sufficient. This will build the default targets, being //vmlinuz// (the uncompressed kernel), //bzImage// (the compressed kernel which we will be using) and //modules// (all of the kernel modules). Since we do not need the uncompressed kernel I usually stick to the "''make bzImage modules''" command. \\ If you want to know more about the available //make// targets, you can run "''make help''" and examine the output. The default build targets are marked by an asterisk (*). |
| |
| ==== Modifying lilo.conf ==== | ==== Modifying lilo.conf ==== |
| |
| Edit ''/etc/lilo.conf'' and add a new section for your new kernel. Remember, your new kernel may not even boot if you made a mistake somewhere, so you will want to leave the sections for your current kernel(s) intact. Your current ''/etc/lilo.conf'' will have a section somewhat like this, near the bottom of the file: <code> | Edit ''/etc/lilo.conf'' and add a new section for your new kernel. Remember, your new kernel may not even boot if you made a mistake somewhere, so you will want to leave the existing sections for your current kernel(s) intact. Your current ''/etc/lilo.conf'' will have a section somewhat like this, near the bottom of the file: <code> |
| image = /boot/vmlinuz | image = /boot/vmlinuz |
| root = /dev/hda1 | root = /dev/hda1 |
| label = linux | label = linux |
| read-only # Non-UMSDOS filesystems should be mounted read-only for checking | read-only # Non-UMSDOS filesystems should be mounted read-only for checking |
| </code> Add another section just below (adding it below will guarantee that your current kernel will remain the default to start): | </code> Add another section just below (adding it below will guarantee that your current - working - kernel will stay the default to boot): |
| <code> | <code> |
| image = /boot/vmlinuz-custom-2.6.27.7 | image = /boot/vmlinuz-custom-2.6.27.7 |
| read-only # Non-UMSDOS filesystems should be mounted read-only for checking | read-only # Non-UMSDOS filesystems should be mounted read-only for checking |
| </code> | </code> |
| After adding a stanza for your new kernel to ''/etc/lilo.conf'' and saving the file, run lilo to activate your changes: <code> | After you have added a section for your new kernel to ''/etc/lilo.conf'' you should save the file, and then run ''lilo'' to activate your changes: <code> |
| lilo | lilo |
| </code> | </code> |
| |
| Now is the time for a reboot, to test the results! In the lilo boot screen, select the "''newkernel''" option instead of the default "''linux''" option.\\ | Now is the time for a reboot, and test that new kernel! When the lilo boot screen appears, select the "''newkernel''" option instead of the default "''linux''" option.\\ |
| If the new kernel boots fine, you can add this line to the top of ''/etc/lilo.conf'' and re-run "lilo": <code> | If your new kernel boots fine, you can make it the default kernel by adding the following line to the top of ''/etc/lilo.conf'' and re-run "lilo": <code> |
| default = newkernel | default = newkernel |
| </code> | </code> |
| | |
| | |
| | ===== Slackware kernel-headers package ===== |
| | |
| | You are going to build and use a new kernel. You may wonder what you need to do with the Slackware //kernel-headers// package.\\ The answer is: **do not remove this package!** |
| | |
| | There are two places where you will find kernel headers; one place is inside the kernel source directory (in our case, the ''/usr/src/linux-2.6.27.7'' directory) and the other place is ''/usr/include/linux''. The //kernel-headers// package usually contains the headers taken from the source of the default Slackware kernel. These particular headers are used when the //glibc// package is built. The fact that the ''kernel-headers'' package installs these files to ''/usr/include/linux'' makes them independent of the header files you find in the kernel source directory. |
| | |
| | <note>As long as you do not upgrade your //glibc// package, you should not upgrade or remove the ''kernel-headers'' package.</note> |
| | |
| | * How do the ''kernel-headers'' and ''glibc'' packages relate?\\ At some point in time you will want to upgrade (recompile!) parts of your system's software. If that software links against glibc (as most core software does), it's successful compilation relies on the presence of the correct kernel headers in ''/usr/include/linux''. It does not matter that you are propably running an entirely different kernel than Slackware's default kernel. The ''kernel-headers'' package reflects the state of the system at the time ''glibc'' was built. If you delete the ''kernel-headers'' package, your running system will in no way be affected, but you will not be able to (re-)compile most software. |
| | |
| | * Do the kernel sources still serve a purpose after you have built your new kernel?\\ In the previous bullet point I told you that the compilation of system software uses the headers located in ''/usr/include/linux''. Likewise, the kernel source tree is required any time you want to compile a 3rd-party kernel module (madwifi, linux-uvc, ndiswrapper, ... the list is endless). You are not limited to compiling a driver for your running kernel. You can build drivers for any kernel as long as its modules tree (below ''/lib/modules'') and sources are present.\\ Let's say you are going to build a module for a kernel whose version you have specified in an environment variable ''$KVER''. For instance, by running <code> |
| | export KVER=2.6.29.1 |
| | </code> During the driver's compilation you will need to have this particular kernel's header files available in the location ''/lib/modules/$KVER/build/include/linux''. The symbolic link ''/lib/modules/$KVER/build'' is created at the time when you install your new kernel and modules.\\ If you delete the kernel sources after you build a kernel, you will not be able to build any "out-of-kernel" (other word for 3rd-party) drivers afterwards. |
| | |
| |
| ===== Other packages that contain kernel modules ===== | ===== Other packages that contain kernel modules ===== |
| |
| Most certainly you will have packages installed that contain kernel modules that are not part of the default kernel. Slackware has "alsa-driver" for instance, and if you installed any wireless driver, these are basically kernel modules too.\\ | Most certainly you will have installed one or more packages containing kernel modules that are not part of the default kernel. Slackware installs the "svgalib-helper" package for instance, and if you installed any wireless driver, these are basically kernel modules too.\\ |
| Now, with the installation of your new kernel, you will lose these modules, and you have to recompile the sources so that the binary modules match the new kernel.\\ | Be aware that by installing and booting into your new kernel, you will no longer have these out-of-kernel modules available. You have to recompile their sources so that the resulting kernel modules match the version of your new kernel.\\ |
| You can get an overview of all packages that have installed a kernel module for your current kernel by running this command (i.e. you must run this command while still running your old kernel): <code> | You can get an overview of all packages that have installed a kernel module for your current kernel by running this command (//note that you must run this command while still running your old kernel//): <code> |
| cd /var/log/packages | cd /var/log/packages |
| grep -l "lib/modules/$(uname -r)" * | grep -l "lib/modules/$(uname -r)" * |
| </code> | </code> |
| All the mentioned packages will need a recompile. | All the listed packages will need a recompile if you want to have their modules available for your new kernel as well. |
| |
| For ALSA you have a choice: either enable the ALSA driver that is part of the kernel you've just downloaded, or leave the kernel configuration like Slackware's: disable all ALSA support in the kernel and instead re-build the alsa-driver package. The 2.6 kernels of Slackware 12.2 have all the ALSA drivers built-in because they will not work with the ALSA driver releases you can install separately. | <note tip>If you rebuild a package containing a kernel module, use **installpkg** rather than **upgradepkg** to install this new package without removing the original version. \\ If you used ''upgradepkg'' this would remove the old kernel module and you may still need this if you ever want to reboot into your old kernel. This trick works under the assumtion that the version of the kernel is part of the //VERSION// of your package, like here: ''svgalib_helper-1.9.25_//2.6.27.7//-i486-1.tgz''</note> |
| | |
| | <note warning>The method described above will leave you **unaware** of any kernel modules that you may have compiled manually instead of creating a package for them. Typically, proprietary graphics drivers such as those from //Nvidia// or //Ati// will cause a few anxious moments if you forget to recompile them for your new kernel before starting X Window... especially when your computer boots into the graphical //runlevel 4// by default. |
| | |
| | In that case, reboot into //runlevel 3//, download the latest version of your graphics driver and compile/install the driver. This will enable you to reboot into your graphical logon. \\ For those who forget, booting into another than the default runlevel is easy: when the LILO screen appears, type the label of your kernel (which was ''newkernel'' in our example above) and after that, type the runlevel number: <key>newkernel</key> <key>Space</key><key>3</key><key>Enter</key></note> |
| | |
| | For ALSA you have a choice: either enable the ALSA driver that is part of the kernel you've just downloaded, or leave the kernel configuration like Slackware's: disable all ALSA support in the kernel and instead re-build the alsa-driver package. The 2.6 kernels of Slackware 12.2 have all the ALSA drivers built-in because they will not work with the ALSA driver releases that you can download and install separately. |
| |
| |
| read-only | read-only |
| # Linux bootable partition config ends | # Linux bootable partition config ends |
| </code></note> | </code> This script is included in the //mkinitrd// package of the Slackware releases after 12.2. |
| | </note> |
| |
| ===== Loading modules on boot ===== | ===== Loading modules on boot ===== |
| |
| <note>If you decide to build your own 2.6 kernel from source, you might get bitten by the fact that there will not be a file called ''/etc/rc.d/rc.modules-$(uname -r)'' - you will have to create it yourself. The ''rc.modules'' usually is a symlink to the ''rc.modules-2.6.27.7-smp''. A typical result from the absence of a rc.modules file for your specific kernel is that your mouse will not be working. Take that behaviour as a hint to create the ''rc.modules'' file! You can take a full copy of any existing ''rc.modules-2.6.xx'' file. If your system does not have any rc file for a 2.6 kernel you can take the one on the Slackware CD as an example:\\ | <note>If you decide to build your own 2.6 kernel from source, you might get bitten by the fact that there will not be a file called ''/etc/rc.d/rc.modules-$(uname -r)'' - you will have to create it yourself. The ''rc.modules'' usually is a symlink to the ''rc.modules-2.6.27.7-smp''. A typical result from the absence of a rc.modules file for your specific kernel is that your mouse will not be working. Take that behaviour as a hint to create the ''rc.modules'' file! You can take a full copy of any existing ''rc.modules-2.6.xx'' file. If your system does not have any rc file for a 2.6 kernel you can take the one on the Slackware CD as an example:\\ |
| ''/source/k/kernel-modules-smp/rc.modules.new''</note> | ''/source/k/kernel-modules-smp/rc.modules.new''. \\ Here's an example in case you would have built a new kernel with version ''2.6.28.8.alien'' and you already had installed a Slackware kernel ''2.6.27.7-smp'': <code> |
| | cp -a /etc/rc.d/rc.modules-2.6.27.7-smp /etc/rc.d/rc.modules-2.6.28.8.alien |
| | </code> The file ''/etc/rc.d/rc.modules-2.6.28.8.alien'' will then be used when your new kernel ''2.6.28.8.alien'' boots.</note> |
| |
| ===== GPG signature ===== | ===== GPG signature ===== |
| </file> If you would have told gnupg to trust this key, the last part would have looked different. To me, adding a trustlevel to this key makes no real sense, except when you've met one of the kernel developers who had the key with him and could present thrustworthy credentials.\\ | </file> If you would have told gnupg to trust this key, the last part would have looked different. To me, adding a trustlevel to this key makes no real sense, except when you've met one of the kernel developers who had the key with him and could present thrustworthy credentials.\\ |
| Nevertheless, the outcome is that the source code archive was indeed signed with the key that you just imported. So, that is good news. | Nevertheless, the outcome is that the source code archive was indeed signed with the key that you just imported. So, that is good news. |
| | |
| | ===== Translations ===== |
| | |
| | * This article has been translated into Spanish by Jorge: [[http://coredump.cl/content/construir-un-kernel | http://coredump.cl/content/construir-un-kernel]] |
