ubuntu-16.10 开始不再使用initd管理系统，改用systemd
systemd 默认读取 /etc/systemd/system 下的配置文件，该目录下的文件会链接/lib/systemd/system/下的文件。
执行 ls /lib/systemd/system 你可以看到有很多启动脚本，其中就有我们需要的 rc.local.service内容如下
# 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
一般正常的启动文件主要分成三部分
[Unit] 段: 启动顺序与依赖关系
[Service] 段: 启动行为,如何启动，启动类型
[Install] 段: 定义如何安装这个配置文件，即怎样做到开机启动
我们需要在尾部添加install段
[Install]
WantedBy=multi-user.target
Alias=rc-local.service
ubuntu-18.04 默认是没有 /etc/rc.local 这个文件的，需要自己创建
sudo touch /etc/rc.local
然后把你需要启动脚本写入 /etc/rc.local ，我们写一些测试的脚本放在里面，以便验证脚本是否生效.
#!/bin/bash
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.
echo "eraser test" > /root/text.log
接下来，重启系统，然后看看 /usr/local/text.log 文件是否存在就知道开机脚本是否生效了。