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NAME | SYNOPSIS | DESCRIPTION | USAGE | EXAMPLE | OPTIONS | SUPPORTED KERNEL FILE TYPES AND OPTIONS | ARCHITECTURE OPTIONS | COLOPHON |
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kexec(8) User Manuals kexec(8)
kexec - directly boot into a new kernel
/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]
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.
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.
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, assuming the user-space supports
kexec-based rebooting, it can be booted to, with a clean shutdown,
using the command:
reboot
Alternatively, it can also be booted to, without calling
shutdown(8), with the command:
kexec -e
-d (--debug)
Enable debugging messages.
-S (--status)
Return 1 if the type (by default crash) is loaded, 0 if
not. 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.
--hotplug
Setup kexec segments such that kernel can safely update
them on CPU/Memory hot add/remove events. If this option is
enabled, kernel does in-kernel update of kexec segments on
CPU/Memory hot add/remove events, thus avoiding the need to
reload kdump kernel.
-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. Ignored on XEN.
-c (--kexec-syscall)
Specify that the old KEXEC_LOAD syscall should be used
exclusively.
-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, so this
is the default.
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.
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.
elf-ppc64
--reuse-cmdline
Use the kernel command line from the running system.
--command-line=string
Set the kernel command line to string.
--append=string
Set the kernel command line to string.
--ramdisk=file
Use file as the initial RAM disk.
--initrd=file
Use file as the initial RAM disk.
--devicetreeblob=file
Specify device tree blob file. Not applicable while
using --kexec-file-syscall.
--dtb=file
Specify device tree blob file. Not applicable while
using --kexec-file-syscall.
--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.
--dt-no-old-root
Do not reuse old kernel root=<device> param while creating
flatten device tree.
This page is part of the kexec-tools (kexec-tools) project.
Information about the project can be found at
⟨https://projects.horms.net/projects/kexec/⟩. If you have a bug
report for this manual page, send it to [email protected].
This page was obtained from the project's upstream Git repository
⟨https://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git⟩
on 2025-08-11. (At that time, the date of the most recent commit
that was found in the repository was 2025-06-23.) If you discover
any rendering problems in this HTML version 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 manual page), send a
mail to [email protected]
Linux April 2006 kexec(8)
Pages that refer to this page: kexec_load(2)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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