Linux timed task cron configuration instructions

Linux timed tasks are: cron, Anacron, at, and most of the cron tasks are used

noun explanation

cron--service name; a daemon that performs a periodic task or waits for some event to be processed under Crond--linux, similar to a scheduled task under Windows; crontab--is a custom scheduled task table

Package Installation

To use the Cron service, install the Vixie-cron package and the Crontabs package first, and the two packages function as follows:

The Vixie-cron package is the main program for Cron. The Crontabs package is a program used to install, uninstall, or list tables used to drive the cron daemon.

　　To see if a cron package is installed: Rpm-qa|grep Vixie-cron

To see if the Crontabs package is installed: Rpm-qa|grep crontabs

If not, execute the following command to install the package (package must exist)
RPM-IVH vixie-cron-4.1-54.fc5*
RPM-IVH crontabs*

If you do not have a local installation package, you can install it online if you have a network connection

Yum Install Vixie-cron
Yum Install Crontabs

See if the Crond service is running

Pgrep Crond or/sbin/service crond status or Ps-elf|grep crond|grep-v "grep"

Crond Service Operations Command

/sbin/service Crond Start//Startup service
/sbin/service Crond stop//Shut down service
/sbin/service crond Restart//Restart service
/sbin/service Crond Reload//Reload Configuration

Configure Scheduled Tasks

Cron has two configuration files, one is a global profile (/etc/crontab), is for system tasks, and a set of configuration files generated by the crontab command (Files under/var/spool/cron), is for a user. Scheduled tasks can be configured to any one of them.

To view the global configuration profile configuration: Cat/etc/crontab

---------------------------------------------
Shell=/bin/bash
Path=/sbin:/bin:/usr/sbin:/usr/bin
Mailto=root
home=/

# Run-parts
* * * * * Root run-parts/etc/cron.hourly
4 * * * Root run-parts/etc/cron.daily
4 * * 0 root run-parts/etc/cron.weekly
4 1 * * Root run-parts/etc/cron.monthly
----------------------------------------------

To view scheduled tasks under a user: Crontab-l or cat/var/spool/cron/user name

Crontab Task Configuration Basic format

　　

* * * * * command
Minutes (0-59) hours (0-23) Date (1-31) month (1-12) week (0-6, 0 for Sunday) command
The 1th column represents minutes 1~59 per minute with * or */1
The 2nd column represents the hour 1~23 (0 means 0 points)
The 3rd column represents the date 1~31
The 4th column represents the month 1~12
5th Column Identification Number Week 0~6 (0 = Sunday)
6th List of commands to run

In any of these values, an asterisk (*) can be used to represent all valid values. For example, an asterisk in a month value means that the command is executed monthly after other constraints have been met.
The short line between integers (-) specifies an integer range. For example, 1-4 means integers 1, 2, 3, 4.
Specify a list with a series of values separated by commas (,). For example, 3, 4, 6, 8 indicate these four specified integers.
A forward slash (/) can be used to specify the interval frequency. Adding/<integer> after a range means that integers can be skipped within the range. For example, 0-59/2 can be used to define every two minutes in the Minutes field. The interval frequency value can also be used with asterisks. For example, the value of */3 can be used in the month field to indicate that the task runs every three months.
The line that starts with the pound sign (#) is a comment and will not be processed

Working with instances

Example 1: command is executed every 1 minutes

Command: * * * * * command

　　

Example 2:3rd and 15 minutes per hour of execution

Command: 3,15 * * * * command

Example 3: Execution at 3rd and 15 minutes from 8 o'clock in the morning to 11.

Command: 3,15 8-11 * * * command

Example 4:3rd and 15 minutes of every two-day 8 o'clock in the morning to 11-point execution

Command: 3,15 8-11 */2 * * command

Example 5:3rd and 15 minutes of each Monday from 8 o'clock in the morning to 11.

Command: 3,15 8-11 * * 1 command

Example 6:21:30 restart of SMB per night

Command: * * * */ETC/INIT.D/SMB restart

Example 7:4:45 restart SMB per month for 1, 10, 22nd

Command: 4 1,10,22 * */ETC/INIT.D/SMB restart

Example 8:1:10 restart SMB per Saturday, Sunday

Command: 1 * * 6,0/ETC/INIT.D/SMB restart

Example 9: Restart SMB every 30 minutes from 18:00 to 23:00 daily

Command: 0,30 18-23 * * */ETC/INIT.D/SMB restart

Example 10: Every Saturday night at 11:00am restart SMB

Command: 0 * * 6/ETC/INIT.D/SMB restart

Example 11: Restart SMB every hour

Command: * */1 * * * */ETC/INIT.D/SMB restart

Example 12: Restart SMB every hour from 11 o'clock to 7 in the morning

Command: * 23-7/1 * * * */ETC/INIT.D/SMB restart

Example 13:4th per month with 11 points per Monday to Wednesday restart SMB

Command: 0 4 * MON-WED/ETC/INIT.D/SMB restart

Example 14:4-point restart of SMB on January 1

Command: 0 4 1 Jan */ETC/INIT.D/SMB restart

Example 15: Execution of scripts within/etc/cron.hourly directory per hour

Command: * * * * *root run-parts/etc/cron.hourly

Description

Run-parts This parameter, if you remove this parameter, you can write a script name to run, not the directory name.

Linux timed task cron configuration instructions