Ubuntu 20.04 – start program after boot

edit or create the rc.local file:

sudo nano /etc/rc.local

#!/bin/bash
<your_program>.sh


exit 0

make rc.local executable:

sudo chmod +x /etc/rc.local

edit /etc/systemd/system/rc-local.service:

sudo nano /etc/systemd/system/rc-local.service

add this content to rc.local.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.

# This unit gets pulled automatically into multi-user.target by
# systemd-rc-local-generator if /etc/rc.local is executable.
[Unit]
Description=/etc/rc.local Compatibility
Documentation=man:systemd-rc-local-generator(8)
ConditionFileIsExecutable=/etc/rc.local
After=network.target

[Service]
Type=forking
ExecStart=/etc/rc.local start
TimeoutSec=0
RemainAfterExit=yes
GuessMainPID=no

[Install]
WantedBy=multi-user.target

enable rc.local by service:

sudo systemctl enable rc-local.service

start rc.local by service:

sudo systemctl start rc-local.service

check the rc.local status:

sudo systemctl status rc-local.service

create file rc.local :