Shulou(Shulou.com)06/01 Report--

Shell background scheduled tasks when the use of crontab, I believe that many inexperienced people do not know what to do, so this paper summarizes the causes of the problem and solutions, through this article I hope you can solve this problem.

The usage of crontab

Syntax: crontab [- u username] |-l |-r |-e |-v

-u: specify the user of crontab job

-l: lists the job of the current crontab

-e: use $EDITOR to edit crontab job

-v: lists the status of the current crontab job. Some shell may not support-v

Crontab file format:

Each line corresponds to one cron job

Each line is divided into six parts, each separated by a space and the same part separated by a comma

Minute hour day_of_month month weekday command

If * is used in the first five fields, it represents all the time steps

Minute:0-59

Hour:0-23 zero stands for zero.

Day_of_month:1-31

Month:1-12

Weekday:0-6 is 0 for Sunday, and 1-6 is for Monday to Saturday.

Command: script or command to be executed

$cat test_cron.sh

#! / bin/sh

# output system time to file time.txt

Echo `date` > > time.txt

# check the current cronjob, and the system indicates that the cronjob of the user habao is not used

$crontab-l

No crontab for habao

# add cronjob

$crontab-e

# not executed every other minute

# display the current system time # write it in the crontab file to make it easy to view the purpose of the scheduled job

* / home/habao/test_cron.sh

# check the current cronjob again

$crontab-l

# DO NOT EDIT THIS FILE-edit the master and reinstall.

# (/ tmp/crontab.3285 installed on Thu Sep 22 16:28:40 2011)

# (Cron version-- $Id: crontab.c,v 2.13 1994-01-17 03:20:37 vixie Exp $)

# display the current system time

* / home/habao/test_cron.sh

# View the output file time.txt

$cat time.txt

Thu Sep 22 16:33:00 CST 2011

Thu Sep 22 16:34:00 CST 2011

Thu Sep 22 16:35:00 CST 2011

Thu Sep 22 16:36:00 CST 2011

Thu Sep 22 16:37:00 CST 2011

Thu Sep 22 16:38:00 CST 2011

Thu Sep 22 16:39:00 CST 2011

To modify the current cronjob, crontab-e

To delete the current cronjob, crontab-r

After reading the above, have you mastered how to use crontab in shell background scheduled tasks? If you want to learn more skills or want to know more about it, you are welcome to follow the industry information channel, thank you for reading!

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