Table of contents
3.crontab scheduled task settings
1 Overview
Task scheduling : refers to specific commands or programs executed by the system at a certain time
Task scheduling classification :
(1) System work: Some important work must be performed repeatedly. Such as virus scanning.
(2) Individual user work: Individual users may want to execute certain programs. Such as backing up the database.
2.crontab service management
Restart the crond service
# systemctl restart crond
3.crontab scheduled task settings
crond [options]
| Options | Function |
| -e | Edit crontab |
| -l | Query crontab tasks |
| -r | Delete all crontab tasks for the current user |
(1) crontab -e , enter the editing interface. This will open vim to edit your work
***** Tasks performed
Parameter Description
| project | meaning | scope |
| First" * " | The minute of the hour | 0-59 |
| the second" * " | What hour of the day | 0-23 |
| The third" * " | Day of the month | 1-31 |
| the fourth" * " | Which month of the year | 1-12 |
| the fifth" * " | day of the week | 0-7 (0 and 7 both represent Sunday) |
(2) Special symbols
special symbols
| special symbols | meaning |
| * | Represents any time. For example, the first "*" means execution every minute for an hour. |
| , | Represents discontinuous time. For example, the "0 8,12,16 * * *" command means that the command will be executed at 8:00, 12:00, and 16:00 every day. |
| - | Represents a continuous time range. For example, the "0 5 * * 1-6" command means executing the command at 5:00 a.m. from Monday to Saturday. |
| */n |
Represents how often it is executed. For example, the " */n * * * * " command means executing the command every 10 minutes. |
(3) Execute commands at a specific time
Execute command at specific time
| time | meaning |
| 45 22 * * * Command | Execute the command at 22:45 every day |
| 0 17 * * 1 command | Execute the command every Monday at 17:00 |
| 0 5 1,15 * * Command | Execute the command at 5:00 am on the 1st and 15th of every month |
| 40 4 * * 1-5 commands | Execute the command every Monday to Friday at 4:40 a.m. |
| */10 4 * * * Command | Execute the command every 10 minutes at 4 am every day |
| 0 0 1,15 * 1 command | The command will be executed on the 1st and 15th of every month, and at 0:00 every 1st. |
Note : It is best not to appear the day of the week and the number at the same time, because they both define days. Very easy to confuse administrators.
for example:
Every minute, append the file list under /home to the /temp/a.txt file
*/1 * * * * ls -l /etc >> /temp/a.txt