centos7 是用Systemd进行系统初始化的，Systemd是linux系统最新的初始化系统，
Systemd服务文件以.service结尾。如果用yum 命令安装的，yum会自动创建nginx.service
直接用命令：

systemcel enable nginx.service

就可设置开机启动
通过源码编译安装的，需要手动建立nginx.service文件

vi /lib/systemd/system/nginx.service

[Unit]
Description=nginx
After=network.target
  
[Service]
Type=forking
ExecStart=/usr/local/nginx/sbin/nginx
ExecReload=/usr/local/nginx/sbin/nginx -s reload
ExecStop=/usr/local/nginx/sbin/nginx -s quit
PrivateTmp=true
  
[Install]
WantedBy=multi-user.target

Description：描述服务
After：描述服务类别
[Service]:服务运行参数设置
Type：forking 是后台运行的形式
ExecStart为服务的具体运行命令
ExecReload为重启命令
ExecStop为停止命令
PrivateTmp=True表示给服务分配独立的临时空间

• 设置开机启动

systemctl enable nginx.service

• 启动nginx服务

systemctl start nginx.service

• 停止开机启动

systemctl disable nginx.service

• 查看服务当前状态

systemctl status nginx.service

• 重启服务

systemctl restart nginx.service

• 查看已启动服务

systemctl list-units --type=service

• 出现问题：

systemctl start nginx
-- Unit nginx.service has begun starting up.
...
systemd[3279]: nginx.service: Failed to execute command: Permission denied
...
systemd[3279]: nginx.service: Failed at step EXEC spawning /home/dev/local/nginx/sbin/nginx: Permission denied

/etc/init.d/nginx start
Failed to start SYSV: NGINX is an HTTP(S) server

说明：直接通过/home/dev/local/nginx/sbin/nginx命令可以启动，但是通过脚本命令无法启动
以上2个问题可能是SELINUX问题：

# This file controls the state of SELinux on the system.
# SELINUX= can take one of these three values:
#     enforcing - SELinux security policy is enforced.
#     permissive - SELinux prints warnings instead of enforcing.
#     disabled - No SELinux policy is loaded.
#SELINUX=enforcing
SELINUX=disabled
# SELINUXTYPE= can take one of these three values:
#     targeted - Targeted processes are protected,
#     minimum - Modification of targeted policy. Only selected processes are protected.
#     mls - Multi Level Security protection.
SELINUXTYPE=targeted

修改SELINUX=disabled即可。