--- name: "kexec" section: "8" platform: "linux" package: "kexec-tools" version: "2.0.32-1" release: "Arch Linux 2026-11-01" platforms: ["linux"] url: "https://new.carta.tech/kexec" --- # kexec(8) directly boot into a new kernel ## 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)](/shutdown/8.md). 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, 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)](/shutdown/8.md), with the command: **kexec** -e ## OPTIONS - **-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)](/shutdown/8.md). - **-f (--force)** Force an immediate **kexec** call, do not call [**shutdown**(8)](/shutdown/8.md) (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. ## 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. **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. ## 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. - **--dt-no-old-root** Do not reuse old kernel root=\ param while creating flatten device tree.