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============================================================================== NETKIT USER MODE KERNEL Version K2.8 ============================================================================== This package provides a User Mode Linux (UML) kernel for use with Netkit virtual machines. === ABOUT THIS KERNEL === A User Mode kernel is a particular piece of software that emulates the kernel of a real host, and yet runs as a standard user space process, namely as a standard application like `xterm'. Emulated features include virtual disks, network interfaces, memory management, scheduling algorithms, and (almost) whatever the kernel of a host machine would provide. This kernel has been configured to enable support for loadable kernel modules, namely drivers and other components that can be attached or removed on the fly from a running kernel. Using modules reduces the overall kernel size, because most features are compiled as separate modules, and minimizes memory consumption and startup time, because unnecessary drivers and features are not enabled until explicitly required. Compiled modules are provided inside the directory `modules/lib/modules/<kernel_version>', where <kernel_version> is the version of the kernel provided with this package. Every virtual machine can be started with its own UML kernel. In principle, nothing forces to use particular combinations of kernels and filesystems. Nevertheless, filesystems may contain tools that have been installed for use with a specific kernel version. It is therefore advised to always use the most recent released kernels and filesystems. === COMPILING A CUSTOM UML KERNEL FOR USE WITH NETKIT === This section describes how to compile an UML kernel from scratch so that it can be used with Netkit. In principle, the procedure to compile a kernel is independent on the underlying Linux distribution. However, some of these instructions are tailored for our development platform, which is a Debian system. 1. PREREQUISITES First of all, you need to have a properly set up building environment. Typically, this involves installing at the very least the following packages: gcc binutils make libc6-dev bison flex You are likely going to compile a cross-architecture kernel. This is the case, for example, when you are building the kernel on a x86_64 (64 bit) platform and want it to be compatible with other i386 (32 bit) hosts. In this case, you would need other packages: libc6-dev-i386 gcc-multilib Yet other packages will be needed to enable specific kernel features and modules, but these highly depend on which of them you choose to enable. The rule of thumb is to check for missing files in compilation errors and install development packages (their names typically end with `-dev') that provide those files. For a Debian system you can perform a search for packages that contain a given file by visiting the URL http://packages.debian.org/file:<path>, where <path> is the name of the file. Cross-compilation may require further actions. For example, some development packages contain files that are specific for a certain architecture (say x86_64), and your target architecture may be different (say i386). In this case, installing system-wide development files is not enough because the compiler will not find the files that are required for the target architecture. In principle, this could be solved by forcedly installing a package for an architecture that is different from your host's, but this is a bad idea as one day it may break the operation of other tools on your system. We therefore provide an `include' directory inside the kernel directory, where you can put all the offending packages without harming your system. The makefile we provide should take care of automatically get the required packages. However, if you still wanted to do it manually, you would proceed as follows: cd $NETKIT_HOME/kernel/include dpkg-deb -x <debian_package> $PWD where <debian_package> is the name of a package that has been manually downloaded in advance. We are aware of at least the following packages causing this kind of problem: libpcap-dev libvdeplug2-dev Remember that some packages are only metapackages, meaning that they only exist to ensure dependence on other packages. As such, they do not contain any files and are not suited to obtain the required development libraries and files. 2. COMPILATION (THE AUTOMATIC WAY) Starting from version K2.6, the kernel package comes with a makefile that helps automating the configuration and compilation process. Consider that the makefile has been conceived for use on a Debian system, and may therefore not operate properly on other distributions. If you are going to use the makefile, all you need to do is to enter the kernel directory and invoke make as follows: cd $NETKIT_HOME/kernel make -f Makefile.devel kernel The makefile automatically takes care of performing all the operations detailed in section COMPILATION (THE MANUAL WAY). You know that the kernel was successfully compiled when the makefile exits without errors and a kernel executable (typically `netkit-kernel' or similar) is created. The makefile may also provide other targets (for example, to automatically build a Netkit kernel package) and supports the specification of some options to tune the build process. If you want to know all of them, you can simply type: cd $NETKIT_HOME/kernel make -f Makefile.devel 3. COMPILATION (THE MANUAL WAY) Compiling a kernel requires performing the following steps. First of all, you need to get a vanilla kernel source tarball. Such files are available at http://www.kernel.org/pub/linux/kernel/v2.6/. Get a kernel version that matches the one provided in the Netkit kernel package, or you may experience compilation faults due to incompatible configurations. Place the kernel package inside `$NETKIT_HOME/kernel' and unpack it by using the following command: tar xjf linux-<kernel_version>.tar.bz2 or, if you got a .tar.gz package: tar xzf linux-<kernel_version>.tar.gz Now you need to apply Netkit-specific patches, which can be found in `$NETKIT_HOME/kernel/patches'. A shortcut to apply all of them at once follows: cd $NETKIT_HOME/kernel/linux-<kernel_version> for CURRENT_PATCH in $NETKIT_HOME/kernel/patches/*.diff; do \ patch -p1 < $CURRENT_PATCH; done If you downloaded the correct kernel version, no unrecoverable failures should be reported by this command. At this point you are ready to configure the kernel. We strongly suggest to use the configuration settings provided with Netkit as a starting point. In order to do so, you need to copy the configuration file that applies for your target architecture. For example, if you want to compile a kernel for i386 (32 bit) hosts, you would use the command: cp $NETKIT_HOME/kernel/netkit-kernel-config-i386 \ $NETKIT_HOME/kernel/linux-<kernel_version>/.config Then, you need to instruct the kernel build files to fetch this configuration: cd $NETKIT_HOME/kernel/linux-<kernel_version> make silentoldconfig ARCH=um SUBARCH=<target_architecture> If you downloaded the correct kernel version, this command should complete automatically and ask no questions. Otherwise, the user is prompted for any configuration settings that mismatch against those provided with the Netkit kernel package. If you needed to alter settings (for example to enable other drivers or features), you would run the following command: make menuconfig ARCH=um SUBARCH=<target_architecture> and save the configuration on exit. At this point you are ready to start the compilation. In order to do so, proceed as follows: cd $NETKIT_HOME/kernel/linux-<kernel_version> make all modules modules_install ARCH=um SUBARCH=<target_architecture> \ INSTALL_MOD_PATH=$NETKIT_HOME/kernel/modules \ CFLAGS+=-I$NETKIT_HOME/kernel/include/usr/include \ LDFLAGS+=-L$NETKIT_HOME/kernel/include/usr/lib If the procedure completes successfully, your UML kernel should be available in the form of an executable file named `linux' inside the kernel sources directory.