Difference between revisions of "Kexec"

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It is also perfectly legal to invoke kexec manually:
It is also perfectly legal to invoke kexec manually:
{{bc|1=# kexec -l /boot/vmlinuz-linux --initrd=/boot/initramfs-linux.img --reuse-cmdline}}
  # kexec -l /boot/vmlinuz-linux --initrd=/boot/initramfs-linux.img --reuse-cmdline
{{bc|1=# kexec -e}}
  # kexec -e

Revision as of 15:51, 17 June 2013

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Kexec is a system call that enables you to load and boot into another kernel from the currently running kernel. This is useful for kernel developers or other people who need to reboot very quickly without waiting for the whole BIOS boot process to finish. Note that there may appear some problems and kexec may not work correctly for you because the devices won't fully reinitiate when using this method.


To install kexec, install the kexec-tools package which is available in the official repositories.

Rebooting using kexec


You will need to create a new unit file, kexec-load@.service, that will load the specified kernel to be kexec'ed[1].

# vim /etc/systemd/system/kexec-load@.service
Description=load %i kernel into the current kernel
Before=shutdown.target umount.target final.target

ExecStart=/usr/bin/kexec -l /boot/vmlinuz-%i --initrd=/boot/initramfs-%i.img --reuse-cmdline


Then enable the service file for the kernel you want to load, for example simply the default kernel linux:

# systemctl enable kexec-load@linux
ln -s '/etc/systemd/system/kexec-load@.service' '/etc/systemd/system/kexec.target.wants/kexec-load@linux.service'

Ensure that the shutdown hook is not part of your initramfs image by removing it from the HOOKS array in /etc/mkinitcpio.conf. If it is, remove it and rebuild your initrd image with mkinitcpio -p linux.

Then to kexec

# systemctl kexec

If you wish to load a different kernel for the next kexec, for example linux-lts, disable the service for the current kernel and enable the one for the new kernel:

# systemctl disable kexec-load@linux
# systemctl enable kexec-load@linux-lts


It is also perfectly legal to invoke kexec manually:

 # kexec -l /boot/vmlinuz-linux --initrd=/boot/initramfs-linux.img --reuse-cmdline
 # kexec -e


1. [systemd-devel] Right way to do kexec

See also