kexec

Load a new kernel

$ kexec [[-l|--load]] [path/to/kernel] --initrd=[path/to/initrd] --command-line=[arguments]

$ kexec [[-l|--load]] [path/to/kernel] --initrd=[path/to/initrd] --reuse-cmdline

$ kexec [[-e|--exec]]

$ kexec [[-u|--unload]]

kexec [-l|--load <kernel>] [options] [--append=<cmdline>] [--initrd[=<file>]]
kexec -u|--unload
kexec -e|--exec
kexec -i|--status

-l, --load <kernel>
    Load kernel image into memory (default action)

-u, --unload
    Unload previously loaded kernel from memory

-e, --exec
    Execute the loaded kernel (reboot directly)

-p, --preserve-context
    Preserve user memory mappings and context

-i, --initrd=<file>
    Specify initramfs/initrd image

-a, --append=<cmdline>
    Append kernel command line parameters

--dtb=<dtb>
    Load device tree blob for ARM/PowerPC

--kexec-on-panic[=<path>]
    Auto-load for panic kernel (kdump)

--noefi
    Disable EFI runtime services usage

-d, --debug
    Enable debug output

-i, --status
    Show status of loaded kernel

-v, --version
    Display version information

-h, --help
    Show help

kexec is a system utility in Linux that enables loading and booting a new kernel image directly from the currently running kernel, bypassing the traditional bootloader and BIOS/UEFI firmware. This results in significantly faster reboots, often in seconds, and is crucial for kernel crash dumping with kdump.

Using the kexec system call (kexec_load(2)), it copies the new kernel, optional initramfs, and device tree blob into reserved memory. The -l option loads the image, -e executes it, and -u unloads. It's commonly used in production for quick kernel updates, testing, or capturing vmcore dumps during panics via /proc/sys/kernel/kexec_load_disabled and kexec_on_panic.

Requires root privileges (CAP_SYS_BOOT) and kexec-tools package. On EFI systems, secure boot may interfere. Misuse can lead to unbootable systems, so backups are essential. Supports purgatory code for memory protection and type-specific loading (e.g., bzImage, ELF).

Requires root and CAP_SYS_BOOT; can brick system with invalid kernel; EFI/Secure Boot issues; not for regular use—test thoroughly; disables watchdog during load.

Kernel parameter kexec_load_disabled=1 blocks loading if set; use sysctl to toggle. Purgatory validates images.

Load: kexec -l /boot/vmlinuz-new --initrd=/boot/initrd-new.img --append='root=/dev/sda1 console=ttyS0'
Exec: kexec -e

Developed by Eric Biederman in 2003 for Linux 2.6; integrated into mainline kernel ~2.6.13; kexec-tools package maintained by coreos; enhanced for EFI, ARM, crash dumping (kdump since 2.6.20).

kexec_load(2), kdump(8), reboot(8), shutdown(8)