gentoo-overlay/sys-apps/kexec-tools/files/kexec.service

[Unit]
Description=Gracefully restart the box
Documentation=man:kexec(8)
After=boot.mount
Before=shutdown.target umount.target final.target
ConditionPathExists=!/nokexec

[Service]
Type=oneshot
RemainAfterExit=yes
EnvironmentFile=/etc/kexec.conf
ExecStart=/usr/sbin/kexec -l /boot/${KNAME} ${KEXEC_OPT_ARGS}
ExecStop=/usr/sbin/kexec -l /boot/${KNAME} ${KEXEC_OPT_ARGS}

[Install]
WantedBy=multi-user.target