NAME | SYNOPSIS | DESCRIPTION | USAGE | EXAMPLE | OPTIONS | SUPPORTED KERNEL FILE TYPES AND OPTIONS | ARCHITECTURE OPTIONS | COLOPHON

kexec(8)                        User Manuals                        kexec(8)

NAME         top

       kexec - directly boot into a new kernel

SYNOPSIS         top

       /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         top

       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         top

       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         top

       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         top

       -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.

       -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.

       -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         top

       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.

ARCHITECTURE OPTIONS         top

       --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.

COLOPHON         top

       This page is part of the kexec-tools (kexec-tools) project.
       Information about the project can be found at [unknown -- if you
       know, please contact man-pages@man7.org] It is not known how to
       report bugs for this man page; if you know, please send a mail to
       man-pages@man7.org.  This page was obtained from the project's
       upstream Git repository 
       ⟨https://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git⟩ on
       2017-03-13.  If you discover any rendering problems in this HTML ver‐
       sion of the page, or you believe there is a better or more up-to-date
       source for the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original man‐
       ual page), send a mail to man-pages@man7.org

Linux                            April 2006                         kexec(8)