kexec - Man Page

• Load a new kernel: kexec -l path/to/kernel --initrd=path/to/initrd --command-line=arguments
• Load a new kernel with current boot parameters: kexec -l path/to/kernel --initrd=path/to/initrd --reuse-cmdline
• Execute a currently loaded kernel: kexec -e
• Unload current kexec target kernel: kexec -u

tldr.sh

/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

To load a kernel, the syntax is as follows:

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:

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:

Alternatively, it can also be booted to, without calling shutdown(8), with the command:

-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.

kdump.conf(5), kexec_load(2), makedumpfile(8), openrc-shutdown(8), vmcore-dmesg(8).