Shell脚本学习-for循环结构2

案例：通过脚本实现仅sshd、rsyslog、crond、network、sysstat服务在开机时自启动。

Linux系统在开机的服务通常工作在文本模式3级别，因此只需要查找3级别以上的开启的服务即可。查看命令：

chkconfig --list |grep 3:on

[root@vm1 ~]# chkconfig --list |grep 3:on

Note: This output shows SysV services only and does not include native
      systemd services. SysV configuration data might be overridden by native
      systemd configuration.

      If you want to list systemd services use 'systemctl list-unit-files'.
      To see services enabled on particular target use
      'systemctl list-dependencies [target]'.

network         0:off   1:off   2:on    3:on    4:on    5:on    6:off
[root@vm1 ~]#

默认情况下开启的服务比较少，只有network。

[root@vm1 ~]# for name in `chkconfig --list |grep 3:on|awk '{print $1}'`;do chkconfig --level 3 $name off;done

Note: This output shows SysV services only and does not include native
      systemd services. SysV configuration data might be overridden by native
      systemd configuration.

      If you want to list systemd services use 'systemctl list-unit-files'.
      To see services enabled on particular target use
      'systemctl list-dependencies [target]'.


[root@vm1 ~]# for name in crond network rsyslog sshd sysstat;do chkconfig --level 3 $name on;done
Note: Forwarding request to 'systemctl enable crond.service'.
Note: Forwarding request to 'systemctl enable rsyslog.service'.
Note: Forwarding request to 'systemctl enable sshd.service'.
error reading information on service sysstat: No such file or directory


[root@vm1 ~]# chkconfig --list |grep 3:on

说明：将默认开启的服务都关闭，然后开启需要开启的服务。

方法2：

[root@vm1 ~]# for name in `chkconfig --list|grep 3:on|awk '{print $1}'|grep -vE "crond|network|sshd|rsyslog|sysstat"`;do chkconfig $name off;done

Note: This output shows SysV services only and does not include native
      systemd services. SysV configuration data might be overridden by native
      systemd configuration.

      If you want to list systemd services use 'systemctl list-unit-files'.
      To see services enabled on particular target use
      'systemctl list-dependencies [target]'.

Linux系统管理员，需要遵循的原则是最小化原则，尽量不安装不使用的软件，尽量不开启不需要开启的服务，只要不用，就不开启。

我们再理解下for循环语句的结构。chkconfig命令获取到取值变量列表，然后for循环语句“遍历”这个列表，进行处理。