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An in-depth analysis of the system task settings of Linux study notes

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This article brings you relevant knowledge about system task settings in Linux, including issues related to the system startup process, system services, self-starting services and scheduled tasks. I hope it will be helpful to everyone.

An in-depth analysis of the system task settings of Linux study notes

System startup process

  • Start the computer's hardware (BIOS)
    • Read time
    • Select Corresponding startup mode (USB HDD EFI)
  • If it is a Linux system, go back to the /boot directory and boot the system to start
  • The computer system starts to start and reads the initialization Configuration file
    • vi /etc/inittab
    • Controls the running level of the computer when starting runlevel
    • ##3Full multiuser mode (multi-user full version mode) 4unused (reserved mode) 5X11 (User Interface Mode) 6reboot (restart mode)
    • id:3initdefault: The default runlevel is 3
    • Start starting the corresponding services and components with runlevel=3
    • Start to boot the public components by default or Service
      • vi /etc/rc.d/rc.sysinit
    • Start loading the service corresponding to runlevel
      • vi /etc/rc3.d
        • K: Services that need to be turned off when shutting down
        • S: Services that need to be turned on when starting up
        • The numbers represent the order of turning on or off
        • All The files are all soft links (shortcuts), and the link address is /etc/init.

      • ##When the startup is completed, all services

      ##System services

      You can use the chkconfig command to view the services of the current virtual machine.
      • By viewing, you can know that different levels correspond to each service and confirm that it will start automatically during this boot.
      • After the boot is completed, you need Use the service (CentOS6) Systemctl (CentOS7) command to control the opening or closing of the service
      Auto-start service at boot

        rc.local
      • (When this file has execution permission, it will be executed automatically after booting) First create the folder where the script is stored
        • mkdir -p /usr/local/scripts
          Create a script file in the folder
        • vi hello.sh
          • Give execution permission
          Go to the /etc/rc.d/rc.local file and add the absolute path to the script
          • Give rc.local execution permissions

      ##chkconfig

      • First cancel the execution permission of rc.local, and then start testing
        chmod  a-x rc.local
          • Create automatic startup at boot Script file
          vi schoolntpdate.sh
        • #!/bin/bash
          #chkconfig:2345 88 99
          #description:schoolntpdate.sh
          
          ##  开机自启动同步时间
          yum info ntp && ntpdate cn.ntp.org.cn
        • Set execution permissions
        • chmod a+x schoolnptdate.sh
          • Copy the script to /etc/init.d directory
          cp schoolntpdate.sh /etc/init.d/
          • Add to service
          chkconfig --add /etc/init.d/schoolntpdate.sh
          • Restart Server
          reboot
      ## Scheduled task

      In the system service center, crond is responsible for periodic tasks

      systemctl status crond.service

        • Add tasks and edit the current user’s task list
        crontab -e
      • Edit task
      星 星 星 星 星  command
      分 时 日 月 周 命令
      第一列表示分钟1~59  每分钟用*或者*/1表示
      第二列表示小时1~23(0表示0点)
      第三列表示日期1~31
      第四列表示月份1~12
      第五列标识号星期0~6(0表示星期天)
      第六列表示要运行的命令
      
      *: 表示任何时间都,实际上就是“每”的意思。可以代表00-23小时或者00-12每月或者00-59分
      -: 表示区间,是一个范围,00 17-19 * * * cmd,就是每天17,18,19的整点执行命令
      ,: 是分割时段,30 3,19,21 * * * cmd,就是每天凌晨3和晚上19,21的半点时刻执行命令
      /n: 表示分割,可以看成除法,*/5 * * * * cmd,每隔五分钟执行一次
    • 30 21 * * * /usr/local/rc.d/Lighttpd restart
      #上面的例子表示每晚21:30重启apache
      
      45 4 1,10,22 * * /usr/local/rc.d/Lighttpd restart
      #上面的例子表示每月1,10,22日的4:45重启apache
      
      10 1 * * 6,0 /usr/local/rc.d/Lighttpd restart
      #上面的例子表示周六、周日的1:10重启apache
      
      0,30 18-23 * * * /usr/local/rc.d/Lighttpd restart
      #上面的例子表示每天的18:00至23:0每隔30分钟重启apache
      
      0 23 * * 6 /usr/local/rc.d/Lighttpd restart
      #上面的例子表示每星期六的11:00重启apache
      
      * */2 * * * /usr/local/rc.d/Lighttpd restart
      #上面的例子表示每两小时重启apache
      
      * 23-7/1 * * * /usr/local/rc.d/Lighttpd restart
      #上面的例子表示晚上的11点到早上的7点之间,每隔一小时重启apache
      
      0 21 4 * mon-wed /usr/local/rc.d/Lighttpd restart
      #上面的例子表示每月的4号与每周一到周三的11点重启apache
      
      0 4 1 jan * /usr/local/rc.d/Lighttpd restart
      #上面的例子表示一月一号的4:00重启apache
      
      --(功能描述:显示年月日时分秒)
      date "+%Y %m %d %H %M %S"
      • Restart crontab to make the configuration take effect
      systemctl restart crond.service
      • View the current scheduled task through crontab -l
      • View the history of the task
      vi /var/spool/mail/root
      • Clear task
      crontab -r
      • Test
      • Create a script that creates a folder
    • #!/bin/bash
      
      dname=`date "+%Y%m%d%H%M%S"`
      mkdir -p ~/$dname
        • Add a scheduled task and create a folder every minute
        crontab -e #编辑定时任务
        • #
          systemctl restart crond.service  #重启生效
          • crontab -l  #查看当前的定时任务
            • Check if created
              • Clear tasks

          Related recommendations: "Linux Video Tutorial"

      0 ##halt (shut down)
      1 Single user mode
      2 Multiuser, without NFS (multi-user mode, but no network status) FS-->FileSystem

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