Difference between revisions of "Kexec"

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==Rebooting using kexec==
==Rebooting using kexec==
{{Note|The {{ic|kexec}} initscript does not use /proc/cmdline unlike the {{ic|kexec-load}} unit file in the next section.}}
First enable kexec
{{bc|1=# rc.d start kexec}}
To kexec, simply reboot as usual:
{{bc|1=# init 6}}
Add {{ic|kexec}} to the {{ic|DAEMONS}} array in {{ic|/etc/rc.conf}} to enable kexec on every reboot.

Revision as of 06:15, 24 October 2012

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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 new kernel to be kexec'ed[1].

# vim /usr/lib/systemd/system/kexec-load.service
Before=shutdown.target umount.target final.target

ExecStart=/sbin/kexec -l /boot/vmlinuz-linux --initrd=/boot/initramfs-linux.img --reuse-cmdline


Then enable the service file

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

To kexec, simply

# systemctl kexec


It is also perfectly legal to invoke kexec manually:

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


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

See also