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schedule a task to be performed once at a time

batch: Schedule jobs to execute once when the system is not heavily loaded

Step 1:#service atd start Start one-time scheduled task at time

1, absolute timing method midnight HH:MM[today]HH: MM [tommorow]HH:mm week HH:MM mm/dd/yy 2, relative timing method

The code is as follows:

now + n minutesnow + n hours

now + n day

Specify that a command be executed today at 5:30 p.m.(assuming 12: 30,9/16/2009) at5:30pmat17:30at17:30 today +5hoursatnow+300 minutes at 17:3016.9.2009at17:309/16/2009

The specified time is not yet up. We can also write the command we want to execute to a file. You can edit/bin/echo"###########">a.txt#at-fone.txt10:30 in the file.

at-f file point in time at/bin/cp/root/*/home/>bin/echo"111111">/root/one.txt

Ctrl+d exit at-l view or atqat-d or atrm delete scheduled tasks

at execution results and configuration files

The result of at is sent by mail to the user who submitted the command

At configuration file: restrict which users can use at command/etc/at.allow If this file exists, then only the users listed in this file can use at command. If this file does not exist, check/etc/at.deny

/etc/at.deny If this file exists, none of the users listed in the file can use the at command.

If neither file exists, only root can use the at command. If both files exist and are empty, all users can use the at command.

periodic scheduled tasks: crond#servicecrondstart Start periodic scheduled tasks

The crond process searches for crond files and loads them into memory

crontab file is a file named after the user in the/var/spool/cron/directory

After the crond process starts, it first checks whether the user has set up the crontab file, and if it does not go to "sleep" state to release system resources, the crond process wakes up every minute,

Check the crontab file to see if there are any commands that need to be executed. After the command is executed, any output will be sent as mail to the crontab owner.

#crontab-e Edit periodic tasks

#crontab-l View scheduled tasks

#crontab-r Delete the current scheduled task

Format of writing plan task book:

The code is as follows:

Time-sharing day month week

[0--59][0--23][1--31][1--12][0--7]（0ro7issun）

*/23,5,71-5

Every two minutes at three, five, seven Monday through Friday.

None of these items can be blank, they must be filled in

If you do not need to specify several of them later, you can use wildcard "*" to indicate

Multiple values can be specified for each time period, separated by commas, 5-6*/3

Command should give absolute path

User must have permission to run crontab

The code is as follows:

/etc/cron.allow/etc/cron.deny

Similar to AT

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