kexec(8) - directly boot into a new kernel
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kexec(8) User Manuals kexec(8) NAME kexec - directly boot into a new kernel SYNOPSIS /sbin/kexec [-v (--version)] [-f (--force)] [-x (--no-ifdown)] [-y (--no-sync)] [-l (--load)] [-p (--load-panic)] [-u (--unload)] [-e (--exec)] [-t (--type)] [--mem-min=addr] [--mem-max=addr] DESCRIPTION kexec is a system call that enables you to load and boot into another kernel from the currently running kernel. kexec performs the function of the boot loader from within the kernel. The primary difference between a standard system boot and a kexec boot is that the hardware initialization normally performed by the BIOS or firmware (depending on architecture) is not performed during a kexec boot. This has the effect of reducing the time required for a reboot. Make sure you have selected CONFIG_KEXEC=y when configuring the kernel. The CONFIG_KEXEC option enables the kexec system call. USAGE Using kexec consists of (1) loading the kernel to be rebooted to into memory, and (2) actually rebooting to the pre-loaded kernel. To load a kernel, the syntax is as follows: kexec -l kernel-image --append=command-line-options --ini‐ trd=initrd-image where kernel-image is the kernel file that you intend to reboot to. Insert the command-line parameters that must be passed to the new ker‐ nel into command-line-options. Passing the exact contents of /proc/cmdline into command-line-options is the safest way to ensure that correct values are passed to the rebooting kernel. The optional initrd-image is the initrd image to be used during boot. It's also possible to invoke kexec without an option parameter. In that case, kexec loads the specified kernel and then invokes shutdown(8). If the shutdown scripts of your Linux distribution support kexec-based rebooting, they then call kexec -e just before actually rebooting the machine. That way, the machine does a clean shutdown including all shutdown scripts. EXAMPLE For example, if the kernel image you want to reboot to is /boot/vmlinux, the contents of /proc/cmdline is root=/dev/hda1, and the path to the initrd is /boot/initrd, then you would use the following command to load the kernel: kexec -l /boot/vmlinux --append=root=/dev/hda1 --ini‐ trd=/boot/initrd After this kernel is loaded, it can be booted to at any time using the command: kexec -e OPTIONS -d (--debug) Enable debugging messages. -S (--status) Return 0 if the type (by default crash) is loaded. Can be used in conjuction with -l or -p to toggle the type. Note this option supersedes other options and it will not load or unload the ker‐ nel. -e (--exec) Run the currently loaded kernel. Note that it will reboot into the loaded kernel without calling shutdown(8). -f (--force) Force an immediate kexec call, do not call shutdown(8) (contrary to the default action without any option parameter). This option performs the same actions like executing -l and -e in one call. -h (--help) Open a help file for kexec. -i (--no-checks) Fast reboot, no memory integrity checks. -l (--load) kernel Load the specified kernel into the current kernel. -p (--load-panic) Load the new kernel for use on panic. -t (--type=type) Specify that the new kernel is of this type. -s (--kexec-file-syscall) Specify that the new KEXEC_FILE_LOAD syscall should be used exclusively. -c (--kexec-syscall) Specify that the old KEXEC_LOAD syscall should be used exclu‐ sively (the default). -a (--kexec-syscall-auto) Try the new KEXEC_FILE_LOAD syscall first and when it is not supported or the kernel does not understand the supplied image fall back to the old KEXEC_LOAD interface. There is no one single interface that always works. KEXEC_FILE_LOAD is required on systems that use locked-down secure boot to verify the kernel signature. KEXEC_LOAD may be also disabled in the kernel configuration. KEXEC_LOAD is required for some kernel image formats and on architectures that do not implement KEXEC_FILE_LOAD. -u (--unload) Unload the current kexec target kernel. If a capture kernel is being unloaded then specify -p with -u. -v (--version) Return the version number of the installed utility. -x (--no-ifdown) Shut down the running kernel, but restore the interface on reload. -y (--no-sync) Shut down the running kernel, but skip syncing the filesystems. --mem-min=addr Specify the lowest memory address addr to load code into. --mem-max=addr Specify the highest memory address addr to load code into. --entry=addr Specify the jump back address. (0 means it's not jump back or preserve context) --load-preserve-context Load the new kernel and preserve context of current kernel dur‐ ing kexec. --load-jump-back-helper Load a helper image to jump back to original kernel. --reuseinitrd Reuse initrd from first boot. --print-ckr-size Print crash kernel region size, if available. SUPPORTED KERNEL FILE TYPES AND OPTIONS Beoboot-x86 --args-elf Pass ELF boot notes. --args-linux Pass Linux kernel style options. --real-mode Use the kernel's real mode entry point. elf-x86 --append=string Append string to the kernel command line. --command-line=string Set the kernel command line to string. --reuse-cmdline Use the command line from the running system. When a panic kernel is loaded, it strips the crashkernel parame‐ ter automatically. The BOOT_IMAGE parameter is also stripped. --initrd=file Use file as the kernel's initial ramdisk. --ramdisk=file Use file as the kernel's initial ramdisk. bzImage-x86 --append=string Append string to the kernel command line. --command-line=string Set the kernel command line to string. --reuse-cmdline Use the command line from the running system. When a panic kernel is loaded, it strips the crashkernel parame‐ ter automatically. The BOOT_IMAGE parameter is also stripped. --initrd=file Use file as the kernel's initial ramdisk. --ramdisk=file Use file as the kernel's initial ramdisk. --real-mode Use real-mode entry point. multiboot-x86 --command-line=string Set the kernel command line to string. --reuse-cmdline Use the command line from the running system. When a panic kernel is loaded, it strips the crashkernel parame‐ ter automatically. The BOOT_IMAGE parameter is also stripped. --module=mod arg1 arg2 ... Load module mod with command-line arguments arg1 arg2 ... This parameter can be specified multiple times. ARCHITECTURE OPTIONS --console-serial Enable the serial console. --console-vga Enable the VGA console. --elf32-core-headers Prepare core headers in ELF32 format. --elf64-core-headers Prepare core headers in ELF64 format. --reset-vga Attempt to reset a standard VGA device. --serial=port Specify the serial port for debug output. --serial-baud=baud_rate Specify the baud rate of the serial port. Linux April 2006 kexec(8)
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