[Ubuntu-20.04.x]让服务的启动命令放在/etc/rc.local文件中可以开机自启动

1.1 系统版本

root@vm7-101:~# head -5 /etc/os-release 
NAME="Ubuntu"
VERSION="20.04.4 LTS (Focal Fossa)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 20.04.4 LTS"
root@vm7-101:~# 
root@vm7-101:~# 
root@vm7-101:~# uname -r
5.4.0-100-generic
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1.2 解决 /etc/rc.local 开机启动问题

查看/lib/systemd/system/rc-local.service文件并进行修改

#### 查看rc-local.service状态（当前是未启动的,你启动也会失败,因为缺少/etc/rc.local文件）
root@vm7-101:~#
root@vm7-101:~# systemctl status rc-local.service
● rc-local.service - /etc/rc.local Compatibility
     Loaded: loaded (/lib/systemd/system/rc-local.service; static; vendor preset: enabled)
    Drop-In: /usr/lib/systemd/system/rc-local.service.d
             └─debian.conf
     Active: inactive (dead)
       Docs: man:systemd-rc-local-generator(8)


#### 查看 /lib/systemd/system/rc-local.service 文件
root@vm7-101:~#
root@vm7-101:~# grep -v "#" /lib/systemd/system/rc-local.service

[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

### 修改 /lib/systemd/system/rc-local.service 文件中的内容
sed 's#ExecStart=/etc/rc.loca#ExecStart=/bin/bash /etc/rc.loca#g' /lib/systemd/system/rc-local.service 
sed -i 's#ExecStart=/etc/rc.loca#ExecStart=/bin/bash /etc/rc.loca#g' /lib/systemd/system/rc-local.service 

### 重新加载一下
systemctl daemon-reload
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创建/etc/rc.local文件

#### 创建文件并加上权限
touch /etc/rc.local
ls -l /etc/rc.local
chmod +x /etc/rc.local

#### 往文件中添加内容
[ $(wc -l /etc/rc.local  | cut -d " "  -f1) -eq 0 ] &&  echo -e '#!/bin/bash\n#\n' >>/etc/rc.local \
                                               ||  sed  -i '1i #!/bin/bash\n#\n' /etc/rc.local 
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启动rc-local.service服务

root@vm7-101:~# systemctl start rc-local.service
root@vm7-101:~# systemctl status rc-local.service
● rc-local.service - /etc/rc.local Compatibility
     Loaded: loaded (/lib/systemd/system/rc-local.service; static; vendor preset: enabled)
    Drop-In: /usr/lib/systemd/system/rc-local.service.d
             └─debian.conf
     Active: active (exited) since Thu 2022-11-17 15:32:20 CST; 4s ago
       Docs: man:systemd-rc-local-generator(8)
    Process: 1460 ExecStart=/bin/bash /etc/rc.local start (code=exited, status=0/SUCCESS)

Nov 17 15:32:20 vm7-101.host.com systemd[1]: Starting /etc/rc.local Compatibility...
Nov 17 15:32:20 vm7-101.host.com systemd[1]: Started /etc/rc.local Compatibility.
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1.3 测试一下

#### 在iptables中添加规则
iptables -t filter -I INPUT -p tcp -s 0.0.0.0/0 -d 0.0.0.0/0 -m tcp --dport 22 -j ACCEPT
iptables -t filter -I OUTPUT -p tcp -s 0.0.0.0/0 -d 0.0.0.0/0 -m tcp --sport 22 -j ACCEPT

#### 将iptables中的规则进行保存到文件中
iptables-save >/iptables

#### 让开机启动时加载关机前保存的iptables数据
cat >>/etc/rc.local<<'EOF'
## Boot restore iptables rules
iptables-restore /iptables
EOF

#### 重启服务器(生产可不能随便重启哈)
reboot

#### 查看rc-local.service服务
systemctl status rc-local.service   # 肯定是启动状态的

#### 查看iptables中是否有规则
## 第一种方法：要用人眼看
iptables -t filter -L INPUT -vn --line-numbers
iptables -t filter -L OUTPUT -vn --line-numbers

## 第二种方法：不报错就Ok
iptables -t filter -C INPUT -p tcp -s 0.0.0.0/0 -d 0.0.0.0/0 -m tcp --dport 22 -j ACCEPT
iptables -t filter -C OUTPUT -p tcp -s 0.0.0.0/0 -d 0.0.0.0/0 -m tcp --sport 22 -j ACCEPT
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