What is the difference between cron and crond? Learn the secrets of different functions in 1 minute

Are you in Linux Are you trying to configure scheduled tasks on your system but confused between "cron" and "crond"?

Yes, many people will wonder:"What's the difference between the two?" Although they look like twins, there are subtle but crucial differences between them if you look closely.

This article will take you deep into their unique features and working principles.

What is cron?

let us start with cron First of all, you must be familiar with this name.

Cron is actually a complete set of Scheduled task scheduling system, whose name comes from the Greek root "chronos", which means time.

cron systemIt is a scheduled task scheduler for the Linux system, which is used to automatically execute specified tasks at a specific time point.

For example, you can schedule the execution of backup scripts every morning, check the system status every hour, etc.

Core functions of cron

The core function of cron is to automate the management and execution of system tasks, which are usually called "scheduled tasksor Scheduled Tasks.

The cron system reads crontab file(cron tables), these files contain task schedules and command lists, cron will automatically execute these tasks at the scheduled time according to the settings in the crontab file.

It can be said,Cron is the "planner" for scheduled task scheduling, responsible for developing the schedule for all tasks.

Using crontab command

In Linux systems, the cron system consists of crontab Commands are used to manage. crontab command, you can add, edit and delete scheduled tasks.

使用 crontab -e Command to enter the editing mode, you can add the tasks you want to execute in the cron table, the format is as follows:

* * * * * /path/to/command

Each "*" symbol represents a different time unit, such as minutes, hours, days, months, and weeks. Through these time configurations, you can control when the task is executed.

What is crond?

Now that we understand the concept of cron, let's take a look at cron. This is the "unsung hero" of the cron system.

crond is the cron system Daemon, is a program that runs continuously in the background, responsible for monitoring the system time and executing the tasks set by the cron system.

Responsibilities of crond

The crond process will start automatically when the system starts and run in the background all the time. Its only task is to execute the tasks in the crontab file at the specified time.

It can be said,crond is the "executor" of the cron system.

Without the crond process, the cron system loses the ability to execute scheduled tasks.

In Linux, you can use the following command to check if the crond process is running:

ps -ef | grep crond

If the crond process is not running, then all scheduled tasks will not be executed. Therefore, it is very important to keep the crond process running normally.

The relationship between cron and crond: service and executor

To better understand the relationship between cron and crond, we can use aLifeExamples in .

Imagine: You have aXiaoHongShu(小红书)” app, which is a massive system that allows users to view and post content at specific times;

Behind this application, there is a program called "Xiaohong Guardian", which is responsible for automatically publishing content in the background.

Cron is like the "Little Red Book", and crond is the "Little Red Guardian".

To summarize the differences between cron and crond:

• cron: Responsible for formulating and managing task schedules and is the "brain" of scheduled task scheduling.
• cron: The background daemon is the "executor" of scheduled tasks and executes tasks according to the schedule in the cron table.

From this perspective, cron is the overall system, and crond is the process that executes the tasks of the system.

crontab file: cron task list

The execution foundation of the cron system is inseparable crontab file, which is where the cron system stores task schedules.

Each user (including the root user) can have his or her own independent crontab file to manage his or her own scheduled tasks.

We can use crontab -l command to view the current user's task list, or use crontab -e to edit the task.

Syntax of crontab file

In the crontab file, each line represents a task, and the format of each line is as follows:

分钟 小时 日期 月份 星期 命令

For example, the following task executes the backup script at 2 am every day:

0 2 * * * /usr/local/bin/backup.sh

This simple example illustrates the powerful automation capabilities of the cron system.

cron and crond: their behind-the-scenes collaboration

In the actual operation of the system, cron and crond are inseparable. Cron is responsible for creating and managing task schedules, while crond continuously monitors time and ensures that tasks are executed at the specified time.

Whenever the system time reaches the preset task time, crond will "wake up" and execute the task.

Why do we need the crond daemon?

The existence of crond ensures that the task is executed on time. It will automatically start every time the system starts and keep running.

If crond stops running, all tasks in the cron system will fail to execute. Therefore, the normal operation of the crond daemon is crucial to the automated management of the system.

Application scenarios in daily system management

The combination of cron and crond is widely used in system management, especially in server environments. The following are some typical application scenarios:

1. Automatic backup: Through cron, you can schedule the server to back up data every day or every week.
2. Automatic cleaning: Set up regular cleanup of log files to prevent the server disk space from being filled up.
3. Monitoring and Alarming: Regularly perform system health checks through cron and send alarm emails when abnormalities are found.

Cron and crond misunderstandings: common questions and answers

Why is the cron job not executed?

Many people find that the cron tasks they set are not executed as expected. The reasons may include the following:

1. The crond process is not started: Make sure crond is running properly.
2. Task configuration error: Check whether the syntax of the crontab file is correct.
3. Path Problem: Make sure the command and script path specified are correct.

How to restart the crond process?

If the crond process fails, you can restart it using the following command:

sudo service crond restart

This command will restart the crond service, ensuring that all tasks run normally.

Conclusion: The indispensability of cron and crond

The perfect combination of cron and crond enables the Linux system to automatically run tasks without human intervention, greatly improving the system's automated management capabilities.

Cron is a time scheduling system that makes plans, while crond is a daemon process that is responsible for executing tasks.

It can be said that the two complement each other and jointly build a powerful and flexible automated task management system.

In daily use, mastering the differences and applications of cron and crond can make you more proficient in server management and achieve more efficient operations.

In the future, you can learn more about advanced usage of the cron system to further optimize and automate your system management processes.

Cron and crond are definitely good partners that every Linux administrator must have.