Details the installation and use of linux timer task crontabs

Install crontab

yum install crontabs

centos7 comes with me and I did not install it manually

Start/Close

service crond start //  Start Services service crond stop //  Shut down services service crond restart //  Restart Service service crond reload //  service crond reload 

Check if the crontab service is set to start on

systemctl list-unit-files | grep enable | grep crond

Add crontab to Startup Autostart

chkconfig crond on
//  perhaps 
systemctl enable crond.service

View crontab status

service crond status //  See crontab Service Status 

Write timed task command format

min hour day month dayofweek command
  branch   time    day    month    What day is today?     command 

&8203;min: Perform the task at the minute of every hour;Value range 0-59

&8203;hour: Perform this task for the first few hours of the day;Value range 0-23

&8203;day: Perform the task on the day of each month;Value range 1-31

&8203;month: Perform this task in the month of each year;Value range 1-12

&8203;dayofweek: Perform the task on the day of the week;Value range 0-6, 0 means weekend

&8203;command: Specify the command to execute

Edit commands by entering them on the command line in two ways: crontab -e Then add the corresponding task, wq exits direct editing /etc/crontab File, that is vi /etc/crontab Add the appropriate task time format

& #8203; *:Represents an arbitrary moment;Hour digits * denote every hour

&8203;n: Represents a specific moment;If hour 5 means hour 5

&8203;n, m: Represents a specific moment;If hour 1,10 means hour 1 and hour 10

&8203;n-m: Represents a time period;Hour digits 1-5 represent 1-5

& #8203; /n: Represents how many units of time are executed once;Hour bits/1 means that commands are executed every 1 hour, or 1-23/1

Chestnut

* 1 * * * ~/clear_cache.sh  : From  1:00  reach  1:59  every other 1 Minute execution 1 Sub-script 
0 * * * * ~/clear_cache.sh  : Hourly  0  Minute execution 1 Sub-script 
*/10 * * * * ~/clear_cache.sh  : every 10 Sub-execution 1 Sub-script 

Script to clean up system cache

Code:

vim ~/clear_cache_logs.txt
sudo sysctl -w vm.drop_caches=3
sudo sysctl -w vm.drop_caches=1
echo `date -R` >> ~/clear_cache_logs.txt
free -lh >> ~/clear_cache_logs.txt

Clean up memory cache And enter the cleanup time and memory leftover logs into the ~/clear_cache_logs.txt Files, easy to view, can be combined crontab Schedule memory cleanup cache Timed tasks of.

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