Ubuntu Manpage: kexec - directly boot into a new kernel

Provided by: kexec-tools_2.0.18-1ubuntu1.1_amd64

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.

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.