kexec
also: kernel execute
A Linux kernel mechanism that allows a running kernel to directly boot into another kernel without going through the BIOS/firmware, skipping the full hardware initialization process.
kexec (kernel execute) is a system call and tool that enables a loaded kernel to boot another kernel without rebooting the machine or reinitializing hardware. This is faster than a traditional reboot because it bypasses BIOS/UEFI and bootloader stages.
The process involves two stages: first, you load a new kernel and initramfs into memory using kexec -l, then execute the jump to it with kexec -e. The running kernel transfers control directly to the new kernel's entry point.
Common use cases include kernel updates with minimal downtime, fast disaster recovery, and live migration of systems. For example: kexec -l /boot/vmlinuz-new --initrd=/boot/initrd-new --append="root=/dev/sda1" loads a new kernel, then kexec -e boots it immediately.