kexec (kernel execute), analogous to the Unix/Linux kernel call exec, is a mechanism of the Linux kernel that allows booting of a new kernel from the currently running one.
Essentially, kexec skips the bootloader stage and hardware initialization phase performed by the system firmware (BIOS or UEFI), and directly loads the new kernel into main memory and starts executing it immediately. This avoids the long times associated with a full reboot, and can help systems to meet high-availability requirements by minimizing downtime. [1] [2]
While feasible, implementing a mechanism such as kexec raises two major challenges:
Support for allowing only signed kernels to be booted through kexec was merged into version 3.17 of the Linux kernel mainline, which was released on October 5, 2014. [3] This disallows a root user to load arbitrary code via kexec and execute it, complementing the UEFI secure boot and in-kernel security mechanisms for ensuring that only signed Linux kernel modules can be inserted into the running kernel. [4] [5] [6]
Kexec is used by LinuxBoot to boot the main kernel from the Linux kernel located in the firmware.
In computing, BIOS is firmware used to provide runtime services for operating systems and programs and to perform hardware initialization during the booting process. The firmware comes pre-installed on the computer's motherboard.
In computing, booting is the process of starting a computer as initiated via hardware such as a physical button on the computer or by a software command. After it is switched on, a computer's central processing unit (CPU) has no software in its main memory, so some process must load software into memory before it can be executed. This may be done by hardware or firmware in the CPU, or by a separate processor in the computer system.
A rootkit is a collection of computer software, typically malicious, designed to enable access to a computer or an area of its software that is not otherwise allowed and often masks its existence or the existence of other software. The term rootkit is a compound of "root" and the word "kit". The term "rootkit" has negative connotations through its association with malware.
GNU GRUB is a boot loader package from the GNU Project. GRUB is the reference implementation of the Free Software Foundation's Multiboot Specification, which provides a user the choice to boot one of multiple operating systems installed on a computer or select a specific kernel configuration available on a particular operating system's partitions.
Unified Extensible Firmware Interface is a specification for the firmware architecture of a computing platform. When a computer is powered on, the UEFI-implementation is typically the first that runs, before starting the operating system. Examples include AMI Aptio, Phoenix SecureCore, TianoCore EDK II, InsydeH2O.
A softmod is a method of using software to modify the intended behavior of hardware, such as computer hardware, or video game consoles in a way that can overcome restrictions of the firmware, or install custom firmware.
udev is a device manager for the Linux kernel. As the successor of devfsd and hotplug, udev primarily manages device nodes in the /dev directory. At the same time, udev also handles all user space events raised when hardware devices are added into the system or removed from it, including firmware loading as required by certain devices.
Homebrew, when applied to video games, refers to software produced by hobbyists for proprietary video game consoles which are not intended to be user-programmable. The official documentation is often only available to licensed developers, and these systems may use storage formats that make distribution difficult, such as ROM cartridges or encrypted CD-ROMs. Many consoles have hardware restrictions to prevent unauthorized development.
coreboot, formerly known as LinuxBIOS, is a software project aimed at replacing proprietary firmware found in most computers with a lightweight firmware designed to perform only the minimum number of tasks necessary to load and run a modern 32-bit or 64-bit operating system.
Advanced Configuration and Power Interface (ACPI) is an open standard that operating systems can use to discover and configure computer hardware components, to perform power management, auto configuration, and status monitoring. It was first released in December 1996. ACPI aims to replace Advanced Power Management (APM), the MultiProcessor Specification, and the Plug and Play BIOS (PnP) Specification. ACPI brings power management under the control of the operating system, as opposed to the previous BIOS-centric system that relied on platform-specific firmware to determine power management and configuration policies. The specification is central to the Operating System-directed configuration and Power Management (OSPM) system. ACPI defines hardware abstraction interfaces between the device's firmware, the computer hardware components, and the operating systems.
A Hackintosh is a computer that runs Apple's operating system macOS on computer hardware that is not authorized for the purpose by Apple. This can also include running Mac software on hardware it is not originally authorized for. This is due to the software license for macOS only permitting its use on in-house hardware built by Apple itself, in this case the Mac line.
In Linux systems, initrd is a scheme for loading a temporary root file system into memory, to be used as part of the Linux startup process. initrd and initramfs refer to two different methods of achieving this. Both are commonly used to make preparations before the real root file system can be mounted.
The EFIsystem partition or ESP is a partition on a data storage device that is used by computers that have the Unified Extensible Firmware Interface (UEFI). When a computer is booted, UEFI firmware loads files stored on the ESP to start operating systems and various utilities.
In the context of free and open-source software, proprietary software only available as a binary executable is referred to as a blob or binary blob. The term usually refers to a device driver module loaded into the kernel of an open-source operating system, and is sometimes also applied to code running outside the kernel, such as system firmware images, microcode updates, or userland programs. The term blob was first used in database management systems to describe a collection of binary data stored as a single entity.
The Linux booting process involves multiple stages and is in many ways similar to the BSD and other Unix-style boot processes, from which it derives. Although the Linux booting process depends very much on the computer architecture, those architectures share similar stages and software components, including system startup, bootloader execution, loading and startup of a Linux kernel image, and execution of various startup scripts and daemons. Those are grouped into 4 steps: system startup, bootloader stage, kernel stage, and init process.
Ksplice is an open-source extension of the Linux kernel that allows security patches to be applied to a running kernel without the need for reboots, avoiding downtimes and improving availability. Ksplice supports only the patches that do not make significant semantic changes to kernel's data structures.
In computing, rebooting is the process by which a running computer system is restarted, either intentionally or unintentionally. Reboots can be either a cold reboot in which the power to the system is physically turned off and back on again ; or a warm reboot in which the system restarts while still powered up. The term restart is used to refer to a reboot when the operating system closes all programs and finalizes all pending input and output operations before initiating a soft reboot.
kdump is a feature of the Linux kernel that creates crash dumps in the event of a kernel crash. When triggered, kdump exports a memory image that can be analyzed for the purposes of debugging and determining the cause of a crash. The dumped image of main memory, exported as an Executable and Linkable Format (ELF) object, can be accessed either directly through /proc/vmcore during the handling of a kernel crash, or it can be automatically saved to a locally accessible file system, to a raw device, or to a remote system accessible over network.
KernelCare is a live kernel patching service that provides security patches and bugfixes for a range of popular Linux kernels that can be installed without rebooting the system.
LinuxBoot is a free software project aimed at replacing most of the Driver Execution Environment (DXE) modules in Unified Extensible Firmware Interface (UEFI) firmware with the Linux kernel. LinuxBoot must run on top of hardware initialisation software in order to start. This can be the Pre-EFI Initialization (PEI) part of UEFI, coreboot, or U-Boot. It can boot Linux through the kexec syscall, but is also able to boot Windows with a different method.
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