root@ubuntu4:~# ls /lib/systemd/system/ | grep 'kexec'
kexec.target
kexec.target.wants
plymouth-kexec.service
systemd-kexec.service
root@ubuntu4:~# cat /lib/systemd/system/kexec.target
#  SPDX-License-Identifier: LGPL-2.1+
#
#  This file is part of systemd.
#
#  systemd is free software; you can redistribute it and/or modify it
#  under the terms of the GNU Lesser General Public License as published by
#  the Free Software Foundation; either version 2.1 of the License, or
#  (at your option) any later version.

[Unit]
Description=Reboot via kexec
Documentation=man:systemd.special(7)
DefaultDependencies=no
Requires=systemd-kexec.service
After=systemd-kexec.service
AllowIsolate=yes

[Install]
Alias=ctrl-alt-del.target
root@ubuntu4:~# cat /lib/systemd/system/kexec.target.wants
cat: /lib/systemd/system/kexec.target.wants: Is a directory
root@ubuntu4:~# ls /lib/systemd/system/kexec.target.wants
plymouth-kexec.service
root@ubuntu4:~# cat /lib/systemd/system/plymouth-kexec.service
[Unit]
Description=Show Plymouth Reboot with kexec Screen
After=getty@tty1.service display-manager.service plymouth-start.service
Before=systemd-kexec.service
DefaultDependencies=no
ConditionKernelCommandLine=!plymouth.enable=0
ConditionKernelCommandLine=!nosplash
ConditionKernelCommandLine=splash

[Service]
ExecStart=/sbin/plymouthd --mode=shutdown --attach-to-session
ExecStartPost=-/bin/plymouth show-splash
Type=forking
root@ubuntu4:~# cat /lib/systemd/system/systemd-kexec.service
#  SPDX-License-Identifier: LGPL-2.1+
#
#  This file is part of systemd.
#
#  systemd is free software; you can redistribute it and/or modify it
#  under the terms of the GNU Lesser General Public License as published by
#  the Free Software Foundation; either version 2.1 of the License, or
#  (at your option) any later version.

[Unit]
Description=Reboot via kexec
Documentation=man:systemd-halt.service(8)
DefaultDependencies=no
Requires=shutdown.target umount.target final.target
After=shutdown.target umount.target final.target

[Service]
Type=oneshot
ExecStart=/bin/systemctl --force kexec