Difference between revisions of "How to compile kernel"
(edited to make it a bit more newbie-friendly) |
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− | + | It should be noted that the default kernel that ships with Salix OS is "generic" and will work in most cases, and no recompiling is necessary. You should only recompile if: | |
* Your system's hardware is not supported by the default kernel | * Your system's hardware is not supported by the default kernel | ||
* You need (want) features only available in newer kernel | * You need (want) features only available in newer kernel | ||
− | * | + | * For fun |
+ | * To get an extra fraction of a percent hardware performance | ||
− | + | Before going ahead, it may be easier (and will in many cases be sufficient to solve the problem) to install the kernel from Slackware current, which will always be relatively recent. | |
+ | |||
+ | The procedure is actually quite simple, as long as you remember to reinstall the bootloader before rebooting. However, it can take a long time Note that all of this should be done with root privileges. | ||
== Preparation == | == Preparation == | ||
First, download appropriate kernel source from http://www.kernel.org | First, download appropriate kernel source from http://www.kernel.org | ||
− | Unpack source into /usr/src/ and symlink /usr/src/linux to that directory | + | Unpack source into /usr/src/ and symlink /usr/src/linux to that directory (changing 3.2.25 to whichever kernel version you are compiling) |
ln -s /usr/src/linux-3.2.35 /usr/src/linux | ln -s /usr/src/linux-3.2.35 /usr/src/linux | ||
+ | |||
+ | If you are compiling the *same* kernel version you already have, perhaps in order to turn on extra features, you can just work in this directory; get the source by installing the kernel-source package from Slaix repositories, if needed. | ||
Then go into that directory, and do | Then go into that directory, and do | ||
make mrproper | make mrproper | ||
− | This is | + | This is a cleaning procedure and will set everything to default. You can work from here, but it is highly recommended to use the working configuration (i.e. the one you've been running on). The default kernel config is found in /proc/config.gz, so copy this file: |
zcat /proc/config.gz > .config | zcat /proc/config.gz > .config | ||
− | Next, you configure your kernel. | + | Next, you configure your kernel. The advantage of using the working configuration is you can probably leave all the options just as they are, but it may be that you need to turn on support for the hardware that doesn't work with the existing kernel; or it may work with the new kernel without changing anything at all. To build the kernel with the working configuration unchanged, do |
− | + | ||
− | + | make oldconfig | |
− | make | + | |
− | to | + | If you do need to change anything, there is a choice of interfaces for the configuration. To use a graphical interface, do |
make gconfig | make gconfig | ||
− | + | for the gtk-based config, or on a KDE system | |
+ | make xconfig | ||
+ | for a qt interface. | ||
+ | make menuconfig | ||
+ | will bring up the ncurses based menu-driven config, which will work even if you're not running X. | ||
+ | |||
+ | The number of different options may appear bewildering, but pretty much all of them can (indeed should) be left unchanged from the working configuration. If in doubt, as a rule of thumb, it is probably best to leave it as is. | ||
== Compiling == | == Compiling == | ||
Once you have configured the kernel to your liking, save and exit. Then do: | Once you have configured the kernel to your liking, save and exit. Then do: | ||
make | make | ||
− | to build the kernel. This will take some | + | to build the kernel. This will take some hours. After it's done, do: |
make modules_install | make modules_install | ||
to install all of the modules. All of the modules will be installed under /lib/modules/version, where 'version' corresponds to the version of the kernel compiled. | to install all of the modules. All of the modules will be installed under /lib/modules/version, where 'version' corresponds to the version of the kernel compiled. | ||
== Finalizing == | == Finalizing == | ||
− | Next | + | Next, copy the created kernel image and system map to the boot directory. |
cp -v arch/x86/boot/bzImage /boot/vmlinuz-version | cp -v arch/x86/boot/bzImage /boot/vmlinuz-version | ||
cp -v System.map /boot/System.map-version | cp -v System.map /boot/System.map-version | ||
− | where 'version' corresponds to the version of the kernel compiled | + | where 'version' corresponds to the version of the kernel compiled. If this is the same version as the existing one (perhaps because you wanted to turn on extra features) choose a version name that distinguishes the two builds, such as version-custom. |
− | + | Assuming the kernel in your working system is the standard one that came with Salix, the new one you just built will also be a 'huge' kernel that doesn't need an initrd, so you can omit the next step. | |
+ | |||
+ | However, if you know you do need to create an initrd.gz file: | ||
/usr/share/mkinitrd/mkinitrd_command_generator.sh -l /boot/vmlinux-version | /usr/share/mkinitrd/mkinitrd_command_generator.sh -l /boot/vmlinux-version | ||
will generate a command that you can then copy and paste. By default, it will output to /boot/initrd.gz. You may want to change this when cutting and pasting so that it will output to /boot/initrd-version.gz. | will generate a command that you can then copy and paste. By default, it will output to /boot/initrd.gz. You may want to change this when cutting and pasting so that it will output to /boot/initrd-version.gz. | ||
− | As a final step, edit /etc/lilo.conf so that it will see the newly created kernel: | + | As a final step, edit /etc/lilo.conf so that it will see the newly created kernel, includinh the 'initrd' line only if you created one: |
image = /boot/vmlinuz-version | image = /boot/vmlinuz-version | ||
root = /dev/sda6 | root = /dev/sda6 | ||
Line 53: | Line 66: | ||
Don't forget to run | Don't forget to run | ||
lilo | lilo | ||
− | to take effect of the new configuration. | + | to take effect of the new configuration; or use whichever tool you prefer to install the bootloader. |
− | That's it. When you reboot, you should see the new kernel | + | That's it. When you reboot, you should see the new kernel in the lilo menu, and everything should work. As a check, after the system reboots itself: |
uname -a | uname -a | ||
− | You should see that the kernel version is indeed what was just made. | + | You should see that the kernel version is indeed what was just made. |
+ | |||
+ | The old kernel is still present, and your bootloader will still include an option to boot with it as a fallback. Once you are certain everything is working properly with the new one, you may wish to remove the old entry from the bootloader and (optionally, with care) delete the old kernel in /boot. | ||
[[Category:User Documentation|Kernel]] | [[Category:User Documentation|Kernel]] |
Revision as of 14:12, 20 March 2014
It should be noted that the default kernel that ships with Salix OS is "generic" and will work in most cases, and no recompiling is necessary. You should only recompile if:
- Your system's hardware is not supported by the default kernel
- You need (want) features only available in newer kernel
- For fun
- To get an extra fraction of a percent hardware performance
Before going ahead, it may be easier (and will in many cases be sufficient to solve the problem) to install the kernel from Slackware current, which will always be relatively recent.
The procedure is actually quite simple, as long as you remember to reinstall the bootloader before rebooting. However, it can take a long time Note that all of this should be done with root privileges.
Preparation
First, download appropriate kernel source from http://www.kernel.org
Unpack source into /usr/src/ and symlink /usr/src/linux to that directory (changing 3.2.25 to whichever kernel version you are compiling)
ln -s /usr/src/linux-3.2.35 /usr/src/linux
If you are compiling the *same* kernel version you already have, perhaps in order to turn on extra features, you can just work in this directory; get the source by installing the kernel-source package from Slaix repositories, if needed.
Then go into that directory, and do
make mrproper
This is a cleaning procedure and will set everything to default. You can work from here, but it is highly recommended to use the working configuration (i.e. the one you've been running on). The default kernel config is found in /proc/config.gz, so copy this file:
zcat /proc/config.gz > .config
Next, you configure your kernel. The advantage of using the working configuration is you can probably leave all the options just as they are, but it may be that you need to turn on support for the hardware that doesn't work with the existing kernel; or it may work with the new kernel without changing anything at all. To build the kernel with the working configuration unchanged, do
make oldconfig
If you do need to change anything, there is a choice of interfaces for the configuration. To use a graphical interface, do
make gconfig
for the gtk-based config, or on a KDE system
make xconfig
for a qt interface.
make menuconfig
will bring up the ncurses based menu-driven config, which will work even if you're not running X.
The number of different options may appear bewildering, but pretty much all of them can (indeed should) be left unchanged from the working configuration. If in doubt, as a rule of thumb, it is probably best to leave it as is.
Compiling
Once you have configured the kernel to your liking, save and exit. Then do:
make
to build the kernel. This will take some hours. After it's done, do:
make modules_install
to install all of the modules. All of the modules will be installed under /lib/modules/version, where 'version' corresponds to the version of the kernel compiled.
Finalizing
Next, copy the created kernel image and system map to the boot directory.
cp -v arch/x86/boot/bzImage /boot/vmlinuz-version cp -v System.map /boot/System.map-version
where 'version' corresponds to the version of the kernel compiled. If this is the same version as the existing one (perhaps because you wanted to turn on extra features) choose a version name that distinguishes the two builds, such as version-custom.
Assuming the kernel in your working system is the standard one that came with Salix, the new one you just built will also be a 'huge' kernel that doesn't need an initrd, so you can omit the next step.
However, if you know you do need to create an initrd.gz file:
/usr/share/mkinitrd/mkinitrd_command_generator.sh -l /boot/vmlinux-version
will generate a command that you can then copy and paste. By default, it will output to /boot/initrd.gz. You may want to change this when cutting and pasting so that it will output to /boot/initrd-version.gz.
As a final step, edit /etc/lilo.conf so that it will see the newly created kernel, includinh the 'initrd' line only if you created one:
image = /boot/vmlinuz-version root = /dev/sda6 initrd = /boot/initrd-version.gz label = "New Kernel" read-only
Don't forget to run
lilo
to take effect of the new configuration; or use whichever tool you prefer to install the bootloader.
That's it. When you reboot, you should see the new kernel in the lilo menu, and everything should work. As a check, after the system reboots itself:
uname -a
You should see that the kernel version is indeed what was just made.
The old kernel is still present, and your bootloader will still include an option to boot with it as a fallback. Once you are certain everything is working properly with the new one, you may wish to remove the old entry from the bootloader and (optionally, with care) delete the old kernel in /boot.