kexec

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
              --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, 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 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.

       -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 exclusively
              (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 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.


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)