kexec
Section: User Manuals (8)
Updated: April 2006
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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.