# systemctl

```bash
systemctl start service 		#开启服务
systemctl stop service  		#关闭服务
systemctl status service 		#显示状态
systemctl restart service 		#重启服务

systemctl enable service 		#开机启动服务
systemctl disable service		#禁止开机启动

systemctl list-units 			#查看系统中所有正在运行的服务
systemctl list-unit-files 		#查看系统中所有服务是否开机启动

systemctl mask service 			#冻结服务
systemctl unmask service 		#解冻服务

systemctl list-dependencies service 	#查看系统中服务的依赖关系
systemctl set-default multi-user.target #开机时不启动图形界面
systemctl set-default graphical.target 	#开机时启动图形界面

systemctl --version      		#查看systemd版本
```

| 状态            | 含义                                                   |
| --------------- | ------------------------------------------------------ |
| active(running) | 表示程序正在执行                                       |
| atcive(exited)  | 执行一次就正常退出的服务,不在系统中执行任何程序        |
| active(waiting) | 正在执行中,处于阻塞状态,需要等待其他程序执行完才能执行 |
| inactive (dead) | 未启动状态                                             |

| 启动状态 | 含义                 |
| -------- | -------------------- |
| inactive | 服务关闭             |
| disable  | 服务开机不启动       |
| enabled  | 服务开机启动         |
| static   | 服务开机启动项被管理 |
| failed   | 服务配置错误         |
| masked   | 服务被锁定           |

systemctl命令管理systemd的资源Unit

systemd的Unit放在用户目录 **/usr/lib/systemd/system (Centos和Ubuntu)** 或者 **/etc/systemd/system (Ubuntu)**。

主要有四种类型文件.mount、.service、.target、.wants

**.mount 文件**

.mount文件定义了一个挂载点，[Mount]节点里配置了What,Where,Type三个数据项

等同于以下命令：

mount -t hugetlbfs /dev/hugepages hugetlbfs

**.service 文件**

.service文件定义了一个服务，分为[Unit]，[Service]，[Install]三个小节。

```bash
[Unit]
Description=OpenBSD Secure Shell server
After=network.target auditd.service
ConditionPathExists=!/etc/ssh/sshd_not_to_be_run

[Service]
EnvironmentFile=/etc/default/ssh
ExecStart=/usr/sbin/sshd -D $SSHD_OPTS
Restart=on-failure

[Install]
Alias=sshd.service
WangtedBy=multi-user.target
===============================================================
[Unit]
Description:描述，
After：在network.target,auditd.service启动后才启动
ConditionPathExists: 执行条件

[Service]
EnvironmentFile:变量所在文件
ExecStart: 执行启动脚本
Restart: fail时重启

[Install]
Alias:服务别名
WangtedBy: 多用户模式下需要的
```

**.target 文件**

.target定义了一些基础的组件，供.service文件调用

**.wants 文件**

.wants文件定义了要执行的文件集合，每次执行，.wants文件夹里面的文件都会执行

# service

```bash
# service被systemctl代替
service -h
service --status-all  #显示所服务的状态
```

| daemon命令             | systemctl命令                 |
| ---------------------- | ----------------------------- |
| service [服务] start   | systemctl start [unit type]   |
| service [服务] stop    | systemctl stop [unit type]    |
| service [服务] restart | systemctl restart [unit type] |

# init

```bash
# init被systemctl代替
```

| init命令 | systemctl命令      | 说明     |
| :------- | :----------------- | :------- |
| init 0   | systemctl poweroff | 系统关机 |
| init 6   | systemctl reboot   | 重新启动 |

| systemctl命令       | 说明                 |
| :------------------ | :------------------- |
| systemctl suspend   | 进入睡眠模式         |
| systemctl hibernate | 进入休眠模式         |
| systemctl rescue    | 强制进入救援模式     |
| systemctl emergency | 强制进入紧急救援模式 |

| init级别 | systemctl target  |
| :------- | :---------------- |
| 0        | shutdown.target   |
| 1        | emergency.target  |
| 2        | rescure.target    |
| 3        | multi-user.target |
| 4        | 无                |
| 5        | graphical.target  |
| 6        | 无                |


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