systemd 进程管理详解

systemd进程管理

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systemd管理的优势

1.最新系统都采用systemd管理（RedHat7，CentOS7，Ubuntu15...）

2.CentOS7 支持开机并行启动服务,显著提高开机启动效率

3.CentOS7关机只关闭正在运行的服务，而CentOS6，全部都关闭一次。

4.CentOS7服务的启动与停止不再使用脚本进行管理，也就是/etc/init.d下不在有脚本。

5.CentOS7使用systemd解决原有模式缺陷，比如原有service不会关闭程序产生的子进程。

systemd相关文件

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systemd控制的相关文件	CentOS6	CentOS7
服务启动的脚本启动路径	/etc/init.d	/usr/lib/systemd/system
开机自启服务存放路径	/etc/rcN.d	/etc/systemd/system/multi-user.target.wants/
默认运行级别配置文件	/etc/inittab	/etc/systemd/system/default.target

CentOS7安装yum安装nginx的默认脚本启动路径

[root@gong ~]# ll /usr/lib/systemd/system/nginx.service
-rw-r--r-- 1 root root 618 Oct  3  2019 /usr/lib/systemd/system/nginx.service

CentOS7开机自启动所在的目录，该目录包含在该级别启动时自启动的服务

[root@gong ~]# ll /etc/systemd/system/multi-user.target.wants/

CentOS7默认运行级别的控制，把它链接到/usr/lib/systemd/system/下面的不同级别，可以实现对不同默认级别的更改

[root@gong ~]# ll /etc/systemd/system/default.target
lrwxrwxrwx 1 root root 41 Apr 23 15:56 /etc/systemd/system/default.target -> /usr/lib/systemd/system/multi-user.target

systemd相关命令

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CentOS6	systemd CentOS7	作用
/etc/init.d/nginx start	systemctl start nginx	启动nginx服务
/etc/init.d/nginx stop	systemctl stop nginx	停止nginx服务
/etc/init.d/nginx status	systemctl status nginx	查看nginx的状态
/etc/init.d/nginx restart	systemctl restart nginx	重启nginx服务
/etc/init.d/nginx reload	systemctl reload nginx	不停止nginx服务，重新加载配置文件
	systemctl is-active nginx	判断nginx服务是否存活
	systemctl mask nginx	禁止运行服务
	systemctl unmask nginx	取消禁止运行服务

CentOS7启动服务

[root@gong ~]# systemctl start nginx

CentOS7关闭服务

[root@gong ~]# systemctl stop nginx

CentOS7查看服务状态

[root@gong ~]# systemctl status nginx
● nginx.service - The nginx HTTP and reverse proxy server
   Loaded: loaded (/usr/lib/systemd/system/nginx.service; enabled; vendor preset: disabled)
   Active: inactive (dead) since Sat 2020-04-25 08:55:55 CST; 12s ago
  Process: 7063 ExecStart=/usr/sbin/nginx (code=exited, status=0/SUCCESS)
  Process: 7060 ExecStartPre=/usr/sbin/nginx -t (code=exited, status=0/SUCCESS)
  Process: 7056 ExecStartPre=/usr/bin/rm -f /run/nginx.pid (code=exited, status=0/SUCCESS)
 Main PID: 7064 (code=exited, status=0/SUCCESS)

Apr 25 08:55:44 gong systemd[1]: Starting The nginx HTTP and reverse proxy server...
Apr 25 08:55:45 gong nginx[7060]: nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
Apr 25 08:55:45 gong nginx[7060]: nginx: configuration file /etc/nginx/nginx.conf test is successful
Apr 25 08:55:45 gong systemd[1]: Started The nginx HTTP and reverse proxy server.
Apr 25 08:55:55 gong systemd[1]: Stopping The nginx HTTP and reverse proxy server...
Apr 25 08:55:55 gong systemd[1]: Stopped The nginx HTTP and reverse proxy server.

Centos7重启服务

[root@gong ~]# systemctl restart nginx

CentOS7不重启服务重新加载配置文件

[root@gong ~]# systemctl reload nginx

CentOS7检查服务是否启动

[root@gong ~]# systemctl is-active nginx
active

禁止取消服务运行

[root@gong ~]# systemctl mask nginx
Created symlink from /etc/systemd/system/nginx.service to /dev/null.
[root@gong ~]# systemctl unmask nginx
Removed symlink /etc/systemd/system/nginx.service.

systemd开机自启动相关命令

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CentOS6	CentOS7	作用
chkconfig --list	systemctl list-unit-files	查看开机自启的服务
chkconfig nginx on	systemctl enable nginx	开机自启
chkconfig nginx off	systemctl disable nginx	关闭开机自启
chkconfig --list nginx	systemctl is-enabled nginx	查看指定的服务是否被开启
chkconfig --add nginx	systemctl daemon-reload	当手写脚本的时候让系统认识

CentOS7查看开机自启动

[root@gong ~]# systemctl list-unit-files

CentOS7设置开机自启,实质上实在创建软链接

[root@gong ~]# systemctl  enable nginx
Created symlink from /etc/systemd/system/multi-user.target.wants/nginx.service to /usr/lib/systemd/system/nginx.service.

CentOS7关闭开机自启

[root@gong ~]# systemctl disable nginx
Removed symlink /etc/systemd/system/multi-user.target.wants/nginx.service.

CentOS7查看指定的服务是否被开启

[root@gong ~]# systemctl is-enabled nginx
disabled

systemd服务状态

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服务状态	状态说明
loaded	服务单元的配置文件已经被处理
active(running)	服务的一个或多个进程在运行中
active(exited)	一次性运行的服务成功被执行并退出(服务运行后完成任务,相关进程会自动退出)
active(waiting)	服务已经运行但在等待某个事件
inactive	服务没有在运行
enable	服务设定为开机运行
disabled	服务设定为开机不运行
static	服务不能被设定开机启动,但可以由其他服务启动该服务

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