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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 cur-
rently 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 architec-
ture) 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 com-
mand-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.
-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
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.
Linux April 2006 kexec(8)
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