huschi.net

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.
       -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 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)