Linux Systemctl is a collection of system management daemon, tools and libraries, to replace System V, service and chkconfig command, the initial process is primarily responsible for controlling the systemd system and service manager. By Systemctl -help you can see that the command is divided into: a query or send control commands to systemd services related Command management unit services, file services, tasks, environment, snapshot-related commands to configure overloading systemd services, system boot off the relevant command.
1 start, restart, stop and reload it checks the service (e.g. httpd.service) state
systemctl start httpd.service
systemctl restart httpd.service
systemctl stop httpd.service
systemctl reload httpd.service
systemctl status httpd.service
Note: When we use systemctl the start, restart, stop and reload command, the terminal will not output anything, status command can only print output.
2. How to activate the service and enable or disable the service at boot time (that is, the system starts mysql.service service automatically on startup)
systemctl is-active mysql.service
systemctl enable mysql.service
systemctl disable mysql.service
3. How shield (it can not be started) or display services (such as ntpdate.service)
systemctl mask ntpdate.service
ln -s /dev/null /etc/systemd/system/ntpdate.service
systemctl unmask ntpdate.service
rm /etc/systemd/system/ntpdate.service
4. List all services
systemctl list-unit-files –type=service
5. 检查某个单元（如 crond.service）是否启用
systemctl is-enabled crond.service
6. 列出所有失败单元
systemctl –failed
7. 列出所有运行中单元
systemctl list-units
8. 列出所有可用单元
systemctl list-unit-files
9. 使用systemctl命令杀死服务
systemctl kill crond
10. 列出所有系统挂载点
systemctl list-unit-files –type=mount
11. 挂载、卸载、重新挂载、重载系统挂载点并检查系统中挂载点状态
systemctl start tmp.mount
systemctl stop tmp.mount
systemctl restart tmp.mount
systemctl reload tmp.mount
systemctl status tmp.mount
12. 在启动时激活、启用或禁用挂载点（系统启动时自动挂载）
systemctl is-active tmp.mount
systemctl enable tmp.mount
systemctl disable tmp.mount
13. 在Linux中屏蔽（让它不能启用）或可见挂载点
systemctl mask tmp.mount
ln -s /dev/null /etc/systemd/system/tmp.mount
systemctl unmask tmp.mount
rm /etc/systemd/system/tmp.mount
14. 列出所有可用系统套接口
systemctl list-unit-files –type=socket
15. 检查某个服务的所有配置细节
systemctl show mysql
16. 获取某个服务（httpd）的依赖性列表
systemctl list-dependencies httpd.service
17. 启动救援模式
systemctl rescue
18. 进入紧急模式
systemctl emergency
19. 列出当前使用的运行等级
systemctl get-default
20. 启动运行等级5，即图形模式
systemctl isolate runlevel5.target
或systemctl isolate graphical.target
21. 启动运行等级3，即多用户模式(命令行)
systemctl isolate runlevel3.target
或systemctl isolate multiuser.target
22. 设置多用户模式或图形模式为默认运行等级
systemctl set-default runlevel3.target
systemctl set-default runlevel5.target
23. 重启、停止、挂起、休眠系统或使系统进入混合睡眠
systemctl reboot
systemctl halt
systemctl suspend
systemctl hibernate
systemctl hybrid-sleep