Linux Task Scheduler

1. types of work scheduling for Linux
   

   At: handles the command to end the transfer only once, and requires the support of the ATD service when executing the AT command.

   Crontab: The set of work cycles is performed continuously, with a cycle time of minutes, hours, weekly, monthly, and yearly.

2. at:

1. First find/etc/at.allow This file, the user written in this file can use at, Users who are not written in this file will not be able to use at.

2. If/etc/at.allow does not exist, look for/etc/at.deny this file, if the user writing in this at.deny can not use at, but not written in the At.deny file user will be able to use at.

3. If none of the two files exist, then only root can use the AT command.

Requires ATD support  /ETC/INIT.D/ATD restart     or service ATD start

At command:


-M: Notify Users by mail

-L: Lists the at schedule for the user on the system

-D: Cancel work in an at schedule

-V: Lists the task list for at

using a more obvious time format

Time format

hh:mm


hh:mm yyyy-mm-dd

HH:MM[AM:PM] [Month] [Date]

hh:m M[AM:PM] +number [Minutes|hours|days|weeks]

    ATQ: Query at Task  atrm Delete task


3.cron task

Crontab [-u username] [-l|-e|-r]

-U: Use ROOT to help other users create/delete crontab work schedules

-E: Editing crontab tasks

-L: Consult the crontab task

-r: Remove all crontab tasks

, there are 6 fields, each of which is delimited directly by the TAB key, and the meanings of the fields are

Minutes (0~59) hours (0~23) Date (1~31) month (1~12) week (0~7) command

The meanings of the various characters are:

*: Any time

,: Split point in time

-: Time period

/: How often

The system's configuration file is in/etc/crontab

Linux Task Scheduler