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 --initrd=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 kernel 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 --initrd=/boot/initrd

After this kernel is loaded, assuming the user-space supports kexec-based rebooting, it can be booted to, with a clean shutdown, using the command:

    reboot

Alternatively, it can also be booted to, without calling shutdown(8), with the command:

    kexec -e

OPTIONS

-d (--debug)
    Enable debugging messages.

-S (--status)
    Return 1 if the type (by default crash) is loaded, 0 if not. 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 kernel.

-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.

--hotplug
    Setup kexec segments such that kernel can safely update them on CPU/Memory hot add/remove events. If this option is enabled, kernel does in-kernel update of kexec segments on CPU/Memory hot add/remove events, thus avoiding the need to reload kdump kernel.

-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. Ignored on XEN.

-c (--kexec-syscall)
    Specify that the old KEXEC_LOAD syscall should be used exclusively.

-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, so this is the default.

    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 during 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 parameter 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 parameter 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 parameter 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.

multiboot2-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 parameter 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.

elf-ppc64

    --reuse-cmdline
        Use the kernel command line from the running system.

    --command-line=string
        Set the kernel command line to string.

    --append=string
        Set the kernel command line to string.

    --ramdisk=file
        Use file as the initial RAM disk.

    --initrd=file
        Use file as the initial RAM disk.

    --devicetreeblob=file
        Specify device tree blob file. Not applicable while using --kexec-file-syscall.

    --dtb=file
        Specify device tree blob file. Not applicable while using --kexec-file-syscall.

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.

--dt-no-old-root
    Do not reuse old kernel root=<device> param while creating flatten device tree.