Kexec

Kexec is a system call that enables loading and booting into another kernel. This is useful for faster reboots that skip the BIOS or UEFI initialisation process.

Installing kexec-tools

The userspace tools required to use it can be installed via

apk add kexec-tools kexec-tools-doc

The tools are not available on all flavors of Alpine, additionally not all kernels are compiled with the kexec syscall enabled. You will most likely want to check your /boot/config-* file for CONFIG_KEXEC=y

Usage

Manually

On a typical Alpine setup, it can be used via:

# kexec -l /boot/vmlinuz-edge --initrd \ /boot/initramfs-edge --reuse-cmdline \ && openrc shutdown # kexec -e

There are no Alpine-specific considerations for Kexec. Please review the man page and existing references below for more details. This page is deliberately kept short in order to avoid duplicating existing documentation.

Automatically on every reboot/shutdown

kexec can be set to run automatically for faster rebooting. This is very useful on servers.

First create two openrc services and edit the BOOTPART, KERNEL, and INITRD variables if not using the defaults:

Contents of /etc/init.d/kexec-load

#!/sbin/openrc-run
description="kexec for faster reboot"
# Define defaults
: "${BOOTPART:=/boot}"
: "${KERNEL:=vmlinuz-edge}"
: "${INITRD:=initramfs-edge}" 

depend() { 
	need localmount
}

start() { 
	:
}

stop() {
	ebegin "kexec: loading kernel for faster reboot"
	kexec -l "${BOOTPART}/${KERNEL}" \
		--initrd "${BOOTPART}/${INITRD}" \
		--reuse-cmdline
	ewend $? Failed.
}

Contents of /etc/init.d/kexec-exec

#! /sbin/openrc-run
description="kexec for faster reboot"
depend() {
	after killprocs savecache mount-ro
}
start() {
	ebegin "Using kexec for faster reboot" 
	kexec -e
	ewend $? No kernel loaded.
	return 0
}

Now give these services execute permission and assign them to the appropriate runlevels:

chmod a+x /etc/init.d/kexec-load chmod a+x /etc/init.d/kexec-exec rc-update add kexec-load default rc-update add kexec-exec shutdown

Reboot and enjoy!

Note: With both of the above service enabled, it's difficult to poweroff the system as it will reboot unless an unsafe shutdown with poweroff -f is used... To get around this temporarily disable either one of the services (e.g. rc-update del kexec-load default)

Installing kexec-tools

Usage

Manually

Automatically on every reboot/shutdown

See also