Introduction to scheduled tasks in Linux system

[root@localhost lianxi]# yum install at -y

[root@localhost lianxi]# service atd start
Redirecting to /bin/systemctl start atd.service

[root@localhost lianxi]# at 11:00 #Create a one-time scheduled taskat> bash /root/wang.sh
at> <EOT> # ctrl+d to exit job 5 at Wed Dec 22 11:00:00 2021
[root@localhost lianxi]# at -l
3 Wed Dec 22 10:20:00 2021 a root
5 Wed Dec 22 11:00:00 2021 a root
[root@localhost lianxi]#
 
[root@localhost lianxi]# atrm 3 #Delete the task with the scheduled task number 3 [root@localhost lianxi]# at -l #View the scheduled task list 5 Wed Dec 22 11:00:00 2021 a root
[root@localhost lianxi]#

[root@localhost lianxi]# uptime #Check how long the system has been up and the average load of the system 10:28:33 up 4 days, 16:13, 2 users, load average: 0.00, 0.01, 0.05

[root@localhost lianxi]# crontab -e
crontab: installing a new crontab
[root@localhost lianxi]# crontab -l
30 3 * * * bash /root/sc.sh
50 7 * * * service sshd start
50 22 * ​​* * service sshd stop
0 12 */5 * * rm -rf /var/ftp/pub/*
30 7 * * 6 service httpd restart
30 17 * * 1,3,5 tar czf /backup/httpd.tar.gz /etc/httpd
30 4 * * * /bin/bash /lianxi/backup/backup_log.sh
[root@localhost lianxi]#

#The first step is to install [root@localhost lianxi]# yum install ntpdate -y
 
#Step 2 [root@localhost lianxi]# date -s "2021-12-22 15:6:12" #Modified time Wednesday, December 22, 2021 15:06:12 CST
 
#Step 3 [root@localhost lianxi]# ntpdate time.windows.com
22 Dec 11:59:38 ntpdate[13102]: step time server 20.189.79.72 offset -11225.674351 sec
[root@localhost lianxi]# date
Wednesday, December 22, 2021 11:59:42 CST

[root@localhost lianxi]# yum install chrony -y #Install [root@localhost lianxi]# service chronyd restart #Restart service Redirecting to /bin/systemctl restart chronyd.service
 
[root@localhost lianxi]# date -s "2021-12-22 15:6:12"
Wednesday, December 22, 2021 15:06:12 CST
 
[root@localhost lianxi]# date
Wednesday, December 22, 2021 12:02:38 CST

[root@lamp-test backup]# pwd
/backup
[root@lamp-test backup]# cat backup_log.sh 
#!/bin/bash
mkdir -p /backup
tar -czf /backup/$(date +%F_%H_%M_%S)-log.tar.gz /var/log/*
find /backup -mtime +7 -type f -name "*.tar.gz" -exec rm -rf {} \;
[root@lamp-test backup]# crontab -l
30 4 * * * bash /backup/backup_log.sh

[root@localhost lianxi2]# ls /etc/cron.*
/etc/cron.deny
 
/etc/cron.d:
0hourly
 
/etc/cron.daily: The script logrotate man-db.cron that needs to be executed on each machine
 
/etc/cron.hourly: Script 0anacron that needs to be executed every hour
 
/etc/cron.monthly: script to be executed every month /etc/cron.weekly: script to be executed every week [root@localhost lianxi2]# cat /etc/cron.deny Users who disable the crond service can write to it

Hitchhiking example:
[root@lamp-test cron.hourly]# pwd
/etc/cron.hourly
[root@lamp-test cron.hourly]# ls
0anacron poweroff.sh
[root@lamp-test cron.hourly]# chmod +x poweroff.sh 
[root@lamp-test cron.hourly]# cat poweroff.sh 
init 0
 
 
 
[root@lamp-test log]# cd /etc/cron.hourly/
[root@lamp-test cron.hourly]# ls
0anacron poweroff.sh
[root@lamp-test cron.hourly]# rm -rf poweroff.sh