systemd 进程管理详解
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
| 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
| 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
| 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
| 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 |