Execute PHP scripts regularly under Linux (detailed explanation of how to use crontab regularly)

Detailed explanation of how to use crontab for scheduled execution

How to use:
crontab [ -u user ] filecrontab [ -u user ] { -l | -r | -e }
Description:
Crontab is used to allow users to execute programs at fixed times or fixed intervals. In other words, it is similar to the user's schedule. -u user refers to setting the schedule of the specified user. The premise is that you must have its permissions (for example, root) to specify other people's schedules. If -u user is not used, it means setting your own schedule.
Parameters:

-e: Execute a text editor to set the schedule. The default text editor is VI. If you want to use another text editor, please set the VISUAL environment variable to specify which text editor to use (for example setenv VISUAL joe)
-r: Delete the current schedule
-l: List the current schedule

The format of the schedule is as follows:
f1 f2 f3 f4 f5 program

Where f1 represents minutes, f2 represents hours, f3 represents the day of a month, f4 represents the month, and f5 represents the day of the week. program represents the program to be executed.
When f1 is *, it means the program will be executed every minute, when f2 is *, it means the program will be executed every hour, and so on
When f1 is a-b, it means that it will be executed from the a-th minute to the b-th minute. When f2 is a-b, it means that it will be executed from the a-th hour to the b-th hour, and so on.
​When f1 is */n, it means that it will be executed every n minutes. When f2 is */n, it means it will be executed every n hours. The rest can be deduced
When f1 is a, b, c,..., it means that the a, b, c,... minutes are to be executed. When f2 is a, b, c,..., it means that the a, b, c... It takes hours to execute, and so on for the rest
Users can also store all settings in a file first and use crontab file to set the schedule.
Example:
Execute /bin/ls:
at the 0th minute of every hour every day of the month 0 7 * * * /bin/ls

Within 12 months, /usr/bin/backup will be executed every 20 minutes from 6 am to 12 am every day:
0 6-12/3 * 12 * /usr/bin/backup

​Send a letter to admin@domain.name:
every day from Monday to Friday at 5:00 pm 0 17 * * 1-5 mail -s "hi" admin@domain.name
​Execute echo "haha"
at midnight every day of the month at 0:20, 2:20, 4:20.... 20 0-23/2 * * * echo "haha"

Note:
When the program is executed at the time you specify, the system will send you a letter showing the contents of the program execution. If you do not want to receive such a letter, please add > /dev after each line with a space. /null 2>&1 will do.

There are basically two ways to create routine commands in crontab :

One is for all users, who can issue work schedules through the crontab -e command;

The other is for system administrators. You can directly modify the /etc/crontab file to directly execute it regularly.

If you need to send a letter to yourself at 12:00 noon every day,

#crontab -e

Enter the vi editing screen to edit your routine commands, enter the following statement

0 12 * * * mail xxx@163.com

There are 5 numbers above, which mean:

Points (0-59)
Hours (0-23)
Date (1-31)
Month (1-12)
Week(0-6)

In addition, if it is [*], it means that all numbers are applicable.

So, the above statement is to execute the command mail xxx@163.com

Example 1:

Send an email to your friend. It will be sent at 23:59 on May 1st. Use:

# crontab -e 59 23 1 5 * mail xxx@163.com

Example 2:

To check related files every 6 minutes, use:

# crontab -e */6 * * * * /home/cheney/test.sh

Delete routine commands:

# crontab -r will delete it

cron
In Linux, tasks can be configured to run automatically during a specified time period, on a specified date, or when the average system load falls below a specified amount. Red Hat Enterprise Linux is preconfigured to run critical system tasks so that the system can be kept updated. For example, the slocate database used by the locate command is updated daily. System administrators can use automated tasks to perform scheduled backups, monitor systems, run custom scripts, and more.

Red Hat Enterprise Linux comes with several tools to automate tasks: cron, at, and batch.

Cron is a daemon process that can be used to schedule the execution of recurring tasks based on a combination of time, date, month, and week.

cron assumes the system is running continuously. If the system is not running when a task is scheduled, the task will not be executed.

To use the cron service, you must have the vixie-cron RPM package installed and the crond service must be running. To determine whether the package is installed, use the rpm -q vixie-cron command. To determine whether the service is running, use the /sbin/service crond status command.

Configure cron tasks

The main configuration file of cron is /etc/crontab, which includes the following lines:

<tt class="COMPUTEROUTPUT">SHELL=/bin/bash
            PATH=/sbin:/bin:/usr/sbin:/usr/bin
            MAILTO=root
            HOME=/
            # run-parts
            01 * * * * root run-parts /etc/cron.hourly
            02 4 * * * root run-parts /etc/cron.daily
            22 4 * * 0 root run-parts /etc/cron.weekly
            42 4 1 * * root run-parts /etc/cron.monthly</tt>

The first four lines are variables used to configure the cron task running environment. SHELL The value of the variable tells the system which shell environment to use (in this case, bash shell); PATH The variable definition is used The path to execute the command. The output of the cron job is mailed to the username defined by the MAILTO variable. If the MAILTO variable is defined as a blank string (MAILTO=""), the email will not be sent. The HOME variable can be used to set the home directory used when executing commands or scripts.

/etc/crontab Each line in the file represents a task, and its format is:

<tt class="COMPUTEROUTPUT">minute   hour   day   month   dayofweek   command</tt>

 

• minute — 分钟，从 0 到 59 之间的任何整数

• hour — 小时，从 0 到 23 之间的任何整数

• day — 日期，从 1 到 31 之间的任何整数（如果指定了月份，必须是该月份的有效日期）

• month — 月份，从 1 到 12 之间的任何整数（或使用月份的英文简写如 jan、feb 等等）

• dayofweek — 星期，从 0 到 7 之间的任何整数，这里的 0 或 7 代表星期日（或使用星期的英文简写如 sun、mon 等等）

• command — 要执行的命令（命令可以是 ls /proc >> /tmp/proc 之类的命令，也可以是执行你自行编写的脚本的命令。）

在以上任何值中，星号（*）可以用来代表所有有效的值。譬如，月份值中的星号意味着在满足其它制约条件后每月都执行该命令。

整数间的短线（-）指定一个整数范围。譬如，1-4 意味着整数 1、2、3、4。

用逗号（,）隔开的一系列值指定一个列表。譬如，3, 4, 6, 8 标明这四个指定的整数。

正斜线（/）可以用来指定间隔频率。在范围后加上 /<integer> 意味着在范围内可以跳过 integer。譬如，0-59/2 可以用来在分钟字段定义每两分钟。间隔频率值还可以和星号一起使用。例如，*/3 的值可以用在月份字段中表示每三个月运行一次任务。

开头为井号（#）的行是注释，不会被处理。

如你在 /etc/crontab 文件中所见，它使用 run-parts 脚本来执行 /etc/cron.hourly、/etc/cron.daily、/etc/cron.weekly 和 /etc/cron.monthly 目录中的脚本，这些脚本被相应地每小时、每日、每周、或每月执行。这些目录中的文件应该是 shell 脚本。

如果某 cron 任务需要根据调度来执行，而不是每小时、每日、每周、或每月地执行，它可以被添加到 /etc/cron.d 目录中。该目录中的所有文件使用和 /etc/crontab 中一样的语法。

<tt class="COMPUTEROUTPUT"># record the memory usage of the system every monday
            # at 3:30AM in the file /tmp/meminfo
            30 3 * * mon cat /proc/meminfo >> /tmp/meminfo
            # run custom script the first day of every month at 4:10AM
            10 4 1 * * /root/scripts/backup.sh</tt>

Example 37-1. crontab example

Users other than root can use the crontab tool to configure cron tasks. All user-defined crontabs are saved in the /var/spool/cron directory and executed using the identity of the user who created them. To create a crontab project as a user, log in as that user and type the crontab -e command using either the VISUAL or EDITOR The editor specified by the environment variable to edit the user's crontab. This file uses the same format as /etc/crontab. When the changes to the crontab are saved, the crontab file is saved according to the username and written to the file /var/spool/cron/username in.

The

cron daemon checks every minute the /etc/crontab file, the etc/cron.d/ directory, and the directory. 🎜>/var/spool/cron

Changes in the directory. If changes are found, they are loaded into memory. This way, you don't have to restart the daemon when a crontab file changes.

Control the use of cron

The /etc/cron.allow and /etc/cron.deny files are used to restrict the use of cron. Both formats using control files are one user per line. No spaces are allowed in both files. The cron daemon (crond

) does not have to be restarted if the usage control file is modified. Use a control file that is read every time a user adds or removes a cron task.

Root can always use cron regardless of what is specified in the usage control file.

If the cron.allow file exists, only users listed in it are allowed to use cron, and cron.deny

The file will be ignored.

If the cron.allow file does not exist, all users listed in cron.deny

are banned from using cron .

Start and stop services

To start the cron service, use the /sbin/service crond start command. To stop the service, use the /sbin/service crond stop

command. It is recommended that you start this service at boot time.

Statement of this Website

The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Hot AI Tools

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress images for free

Clothoff.io

AI clothes remover

AI Hentai Generator

Generate AI Hentai for free.

Show More

Hot Article

R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)

2 weeks ago By 尊渡假赌尊渡假赌尊渡假赌

Repo: How To Revive Teammates

1 months ago By 尊渡假赌尊渡假赌尊渡假赌

Hello Kitty Island Adventure: How To Get Giant Seeds

4 weeks ago By 尊渡假赌尊渡假赌尊渡假赌

How Long Does It Take To Beat Split Fiction?

3 weeks ago By DDD

R.E.P.O. Save File Location: Where Is It & How to Protect It?

3 weeks ago By DDD

Show More

Hot Tools

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

God-level code editing software (SublimeText3)

Show More

Hot Topics

Where is the login entrance for gmail email?

7338

9

Java Tutorial

1627

14

CakePHP Tutorial

1352

46

Laravel Tutorial

1265

25

PHP Tutorial

1210

29

Show More

Related knowledge

PHP 8.4 Installation and Upgrade guide for Ubuntu and Debian Dec 24, 2024 pm 04:42 PM

PHP 8.4 brings several new features, security improvements, and performance improvements with healthy amounts of feature deprecations and removals. This guide explains how to install PHP 8.4 or upgrade to PHP 8.4 on Ubuntu, Debian, or their derivati

deepseek web version entrance deepseek official website entrance Feb 19, 2025 pm 04:54 PM

DeepSeek is a powerful intelligent search and analysis tool that provides two access methods: web version and official website. The web version is convenient and efficient, and can be used without installation; the official website provides comprehensive product information, download resources and support services. Whether individuals or corporate users, they can easily obtain and analyze massive data through DeepSeek to improve work efficiency, assist decision-making and promote innovation.

How to install deepseek Feb 19, 2025 pm 05:48 PM

There are many ways to install DeepSeek, including: compile from source (for experienced developers) using precompiled packages (for Windows users) using Docker containers (for most convenient, no need to worry about compatibility) No matter which method you choose, Please read the official documents carefully and prepare them fully to avoid unnecessary trouble.

How To Set Up Visual Studio Code (VS Code) for PHP Development Dec 20, 2024 am 11:31 AM

Visual Studio Code, also known as VS Code, is a free source code editor — or integrated development environment (IDE) — available for all major operating systems. With a large collection of extensions for many programming languages, VS Code can be c

How do you parse and process HTML/XML in PHP? Feb 07, 2025 am 11:57 AM

This tutorial demonstrates how to efficiently process XML documents using PHP. XML (eXtensible Markup Language) is a versatile text-based markup language designed for both human readability and machine parsing. It's commonly used for data storage an

PHP Program to Count Vowels in a String Feb 07, 2025 pm 12:12 PM

A string is a sequence of characters, including letters, numbers, and symbols. This tutorial will learn how to calculate the number of vowels in a given string in PHP using different methods. The vowels in English are a, e, i, o, u, and they can be uppercase or lowercase. What is a vowel? Vowels are alphabetic characters that represent a specific pronunciation. There are five vowels in English, including uppercase and lowercase: a, e, i, o, u Example 1 Input: String = "Tutorialspoint" Output: 6 explain The vowels in the string "Tutorialspoint" are u, o, i, a, o, i. There are 6 yuan in total

BITGet official website installation (2025 beginner's guide) Feb 21, 2025 pm 08:42 PM

BITGet is a cryptocurrency exchange that provides a variety of trading services including spot trading, contract trading and derivatives. Founded in 2018, the exchange is headquartered in Singapore and is committed to providing users with a safe and reliable trading platform. BITGet offers a variety of trading pairs, including BTC/USDT, ETH/USDT and XRP/USDT. Additionally, the exchange has a reputation for security and liquidity and offers a variety of features such as premium order types, leveraged trading and 24/7 customer support.

Ouyi okx installation package is directly included Feb 21, 2025 pm 08:00 PM

Ouyi OKX, the world's leading digital asset exchange, has now launched an official installation package to provide a safe and convenient trading experience. The OKX installation package of Ouyi does not need to be accessed through a browser. It can directly install independent applications on the device, creating a stable and efficient trading platform for users. The installation process is simple and easy to understand. Users only need to download the latest version of the installation package and follow the prompts to complete the installation step by step.

See all articles