Linux delay and timing operation

1, at---System delay task Launch command

At time
>command---Mission instructions
>ctrl+d---launch a mission

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AT-L---list delay task ID

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At-r ID---Delete change ID task

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AT-M---to generate messages without output commands

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AT-M---Let the command with output not produce mail

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AT-C ID---View the execution action of this ID delay task

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The user blacklist is present by default and can be set by modifying the configuration file blacklist
Vim/etc/at.deny---Default is blank and takes effect when the whitelist does not exist
Student---Prohibit student use at command

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The user whitelist does not exist by default in the system and must be established by itself, but when the whitelist is established, only users and root users in the whitelist can execute the AT command, and the blacklist will expire immediately.
Vim/etc/at.allow

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2, Cron---timed tasks, cron This program is provided by Cron.service, write program time and event is permanently saved
CRONTAB-E---immediate effect

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Crontab-l---List the current user's cron tasks
Crontab-r---Delete the current user's cron task 650) this.width=650; "Src=" Https://s5.51cto.com/oss/201711/02/28 826f102281bea6ec2ec9d97e917fd7.png-wh_500x0-wm_3-wmp_4-s_3702611923.png "title=" Screenshot from 2017-11-01 19-38-02.png "alt=" 28826f102281bea6ec2ec9d97e917fd7.png-wh_ "/>

Cron Black and white list, the system is only blacklisted by default, when the whitelist blacklist is invalid
/etc/cron.deny

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(1) File method definition Crontab
Vim/var/spool/cron/username---Cron with a user name, the file name must match the user name
Time-of-day month-week action

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(2) Vim/etc/cron.d/filename---Set up multiple user identities to perform cron
Time-of-day month-week user action
Time-of-day month-week user action

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(3) Script mode:
#!/bin/bash
Cat >>/etc/cron.d/westos <<end
* * * * * * Root touch/mnt/{1..2}
* * * * * * Student touch/mnt/file{2..4}

End

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View

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3. System temporary file Management---cache cleanup
Vim/usr/lib/tmpfiles.d/filename.conf
File type path permissions user, group cleanup cache time
d/mnt/westos/777 Root root 20s
Systemd-tmpfiles--create/usr/lib/tmpfiles.d/*---Create command
Systemd-tmpfiles--clean/usr/lib/tmpfiles.d/*---Execute the command,

In each execution of the command is executed first, in the execution of the second, the time to clean up the cache is 20s, after the file is established to clean up, otherwise invalid, the second picture is changed to 40s, is after 40s can clean, otherwise invalid.

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Linux delay and timing operation