Ubuntu-18.04设置开机启动脚本

　　参考：https://www.cnblogs.com/defifind/p/9285456.html

　　　　   http://www.cnblogs.com/airdot/p/9688530.html

　　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

　　打开脚本/lib/systemd/system/rc.local.service  添加末尾几行

[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
elias=rc-local.service

　　PS：实际测试无需添加最后三行也能实现

　　最后增加字段[Install]否则在enable的时候可能会报一下错误，虽然报一下错误后开机自启程序还是正常的

The unit files have no installation config (WantedBy, RequiredBy, Also, Alias
settings in the [Install] section, and DefaultInstance for template units).
This means they are not meant to be enabled using systemctl.
Possible reasons for having this kind of units are:
1) A unit may be statically enabled by being symlinked from another unit's
   .wants/ or .requires/ directory.
2) A unit's purpose may be to act as a helper for some other unit which has
   a requirement dependency on it.
3) A unit may be started when needed via activation (socket, path, timer,
   D-Bus, udev, scripted systemctl call, ...).
4) In case of template units, the unit is meant to be enabled with some
   instance name specified.

　　创建启动文件/etc/rc.local(默认无该文件)

#!/bin/sh -e
touch /tmp/test

　　增加执行权限

chmod +x /etc/rc.local

　　PS：需要#!/bin/sh -e否则可能不生效

　　设置软连接

ln -s /lib/systemd/system/rc.local.service /etc/systemd/system/

　　重启如果在/tmp目录下面创建了test文件则代表设置开启启动成功

　　启动服务并设置开启自启动

systemctl start rc-local
systemctl enable rc-local

　　重启服务器测试，可以通过命令查看自启动状态以及自启动执行时候的报错等信息

systemctl status rc-local

　　如果启动rc-local报错

journalctl -xe

　　

单元已失败

　　检查/etc/rc.local文件配置，是否有非英文状态输入的字符