What is a Daemon in linux? Linux persistent processes explained.

What is a Daemon in linux? Linux persistent processes explained.

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Have you ever wondered about the unseen mechanisms that keep your computer running smoothly? If you’ve ever delved into Linux, you might have stumbled upon the term ‘daemon’ and been piqued by its enigmatic nature. These daemons, much like the silent engine of a car, work tirelessly in the background, managing tasks and services that ensure our systems run efficiently. But what exactly is a daemon in Linux? How are they born, and what part do they play in web services?

In this comprehensive blog post, we aim to unravel these mysteries and shed light on the captivating world of daemons. We’ll investigate their role in web services, explore their function across different operating systems, and guide you through the steps involved in their creation. So, fasten your seatbelts and prepare to dive deep into the intriguing world of daemons in computing!

TL;DR What is a daemon in Linux?

A daemon in Linux is a background process that operates autonomously, performing tasks without user intervention. They are the silent heroes of computing, managing tasks and services that ensure our systems run smoothly.

Understanding Daemons

Let’s begin by addressing a fundamental question: What is a daemon in the context of Linux computing? Simply put, a daemon is a background process that operates autonomously, performing tasks without user intervention. Imagine a diligent office assistant, always ready to handle your requests, yet never demanding your attention – that’s a daemon for you!

Daemons are akin to the backstage crew in a theater production. They operate behind the scenes, handling service requests, managing tasks, and ensuring that everything runs smoothly. For instance, when you send a print command, it’s a print daemon that takes up the job, sending your document to the printer while you continue with your other tasks.

Common Daemons in Linux

Many common processes that run on your Linux system are, in fact, daemons. Consider the crond daemon, for instance. It’s responsible for executing scheduled tasks. Or the sshd daemon, which handles secure shell (SSH) remote login requests. These daemons, among others, play vital roles in the smooth operation of your system.

Daemons are particularly significant in Unix and Linux utility programs. They act as the backbone of many essential computing services, operating silently and efficiently. From managing system logs with the syslogd daemon to handling mail services with the postfix daemon, these background processes are integral to the functionality and efficiency of our systems.

Daemons in Web Services

As we transition from general computing to the specialized field of web services, the pivotal role of daemons remains evident. Let’s delve into the example of the HTTP daemon (httpd). This silent worker is akin to a diligent receptionist at a bustling hotel, incessantly receiving requests from guests (web clients), and ensuring they are directed to the appropriate room (webpage).

Thread-Based Approach of httpd

So, how does the httpd daemon manage to efficiently handle a multitude of requests? The secret is in its ability to utilize threads. Each incoming request is handled by a separate thread, much like a well-staffed reception catering to multiple guests simultaneously. This approach enables efficient request handling and load balancing, ensuring that the web server remains responsive even under heavy traffic.

Event-Driven Architecture in Nginx

However, the world of web services is not confined to Apache’s httpd. We also have the Nginx HTTP daemon, which employs an event-driven architecture. Picture a highly skilled juggler, managing multiple balls (requests) in the air, handling each as it comes. This approach allows Nginx to handle a high number of simultaneous connections with minimal resource usage.

The Role of Daemons in System Security

Beyond efficiency, daemons also contribute to system security. By managing request handling, they act as gatekeepers, ensuring that only legitimate requests are processed. This role is vital in preventing unauthorized access and maintaining the integrity of the web service.

Modern daemons, whether it’s Apache’s httpd or Nginx, have evolved to use threads and event-driven architectures. This evolution enables them to handle requests more efficiently, solidifying their indispensable role in the realm of web services.

Daemon Background

Just like an artist requires a canvas to bring their imagination to life, daemons need an operating system (OS) to function. The OS provides the essential services required for daemons to operate. However, the behavior of daemons varies across different operating systems, much like how an artist’s style might differ depending on the canvas they’re using.

Daemons in Unix and Linux

Let’s delve into Unix and Microsoft Windows, two widely used operating systems. In Unix-like systems, including Linux, daemons are background processes that start at system boot and continue running until the system is shut down. They are typically initiated by the init process, the first process that starts when a Unix-like system boots up, and the parent of all other processes. For instance, the sshd daemon, responsible for secure remote logins, starts at boot and waits for incoming connections.

Daemons in Windows

In contrast, Windows adopts a different approach. Daemons in Windows, known as ‘services’, are managed by the Service Control Manager. They can be set to start at boot, or manually started and stopped by users or other services. A case in point is the Windows Update service, which checks for updates and installs them.

Regardless of the operating system, running daemons necessitates a multitasking environment. This is because daemons need to operate in the background while other processes run in the foreground. Understanding how daemons work is crucial to comprehending the Linux OS kernel structure and system architecture. It’s akin to understanding the inner workings of a clock; once you comprehend how the gears (daemons) function, you’ll have a better grasp of how the entire clock (system) operates.

At its core, while daemons are a universal concept in computing, their behavior and implementation can differ based on the characteristics of the operating system they run on. This variation is a testament to the flexibility and adaptability of daemons in catering to different system needs.

Creating Daemons in Linux

Having explored the definition of a daemon and its role across different operating systems, it’s time to delve into the process of creating a daemon in Linux. If you’ve ever pondered, ‘How does a Linux daemon come to life?’, prepare for an enlightening exploration!


Creating a daemon in Linux can be likened to baking a cake. There are several steps to follow, each one as crucial as the next to the final product. Just as you need to mix the ingredients, preheat the oven, and monitor the baking time to create a delicious cake, creating a daemon involves an initialization process, forking, and some additional steps.

The initialization process is akin to preparing your ingredients before baking. It involves setting up the daemon, including defining its tasks and services.


Next comes forking, a concept that might sound peculiar to non-programmers but is a standard procedure in computer programming. Forking is like dividing your cake batter into individual cake pans. In the context of daemons, it involves creating a new process by duplicating the existing one. The original process is the parent, and the new one is the child. This child process is what becomes the daemon.

File Descriptor Closure and Directory Alteration

The child process then undergoes some changes to become a full-fledged daemon. This is where file descriptor closure and directory alteration come into play. Consider these as the baking and cooling stages of your cake. The file descriptors (channels that the process uses to communicate with files and devices) are closed to free up the system’s resources. The directory is then changed to the root directory to prevent the daemon from keeping any directory in use that may be on a mounted file system.

The creation of daemons in Linux involves a complex and well-defined process, much like baking a cake. Each step, from initialization to forking, file descriptor closure, and directory alteration, is crucial for the daemon’s functionality. Understanding this process gives us a deeper appreciation for these silent workhorses of our computing systems.

Daemon Examples

To truly grasp the role of daemons in computing, it’s beneficial to delve into some tangible examples. Imagine daemons as diligent workers in a vast factory. Each worker has a specific task to perform, and collectively, they ensure the smooth operation of the factory. In the same vein, each daemon has a specific function, and together, they ensure the seamless operation of your computer system.

Udev Daemon

One of the primary roles of daemons is responding to alerts from the operating system. For instance, when you plug in a USB device, the udev daemon receives an alert from the Linux kernel. It then manages the device nodes in the /dev directory, ensuring that your system recognizes the new device. It’s akin to a vigilant security guard, ever watchful for new arrivals and ensuring they’re properly checked in.

Crond Daemon

Another example of a daemon is the crond daemon, which manages scheduled tasks. It’s like a reliable personal assistant, always ensuring that tasks are executed at the right time. Every minute, crond checks for any tasks scheduled to run at that time and executes them. This functionality is crucial for tasks like system backups and updates, which need to be performed regularly.

You might have noticed that these daemon names end with a ‘d’. This is a convention in Unix-like systems where the ‘d’ stands for ‘daemon’. So, crond is the ‘cron’ daemon, sshd is the ‘ssh’ daemon, and so on.

These examples illustrate the diverse roles of daemons in computing. From managing device nodes with udev to handling scheduled tasks with crond, daemons perform a wide range of functions that are crucial to the smooth operation of our computer systems. This highlights their ubiquity and importance in the realm of computing.

The History and Evolution of Daemons

The term ‘daemon’ might seem like it’s been plucked from a fantasy novel, but its roots are firmly planted in the world of technology. The term was first coined in the realm of computing by the programmers of the Massachusetts Institute of Technology’s (MIT) Project MAC. These pioneers drew inspiration from Maxwell’s demon, a thought experiment in physics, where a hypothetical ‘demon’ controls a door between two rooms of gas molecules to create a temperature difference.

Much like Maxwell’s hypothetical demon, daemons in computing are background processes that silently manage tasks. Over time, the term has evolved and is now used to denote any background process that operates independently of user control.

Interestingly, the term ‘daemon’ was later back-fitted into an acronym: Disk And Execution MONitor. This playful twist lends a technical explanation to the term but is more of a whimsical nod to the term’s origins than a strict definition.

The term ‘daemon’ in computing represents a fascinating blend of technology and culture. It mirrors the creativity and imagination of the early pioneers of computing, who drew inspiration from diverse fields. This cultural and historical significance adds an extra layer of intrigue to these unseen and often underappreciated workhorses of our computer systems.

The term ‘daemon’ in computing boasts a rich and fascinating history. From its origins at MIT to its evolution into a universal term for background processes, the story of daemons bears testament to the fusion of technology and culture in the world of computing.

Daemon Recap: The Silent Engine of Computing

Just as the engine of a car silently powers it, allowing you to enjoy a smooth ride, daemons are the silent yet powerful forces that keep our computer systems running efficiently. They are the diligent office assistants, the backstage crew, and the vigilant security guards of the computing world, silently managing tasks and services without demanding our attention.

Daemons behave differently across different operating systems. In Unix-like systems, including Linux, they start at system boot and remain running until the system is shut down. In contrast, Windows services can be manually started and stopped by users or other services.

Creating a daemon in Linux involves a well-defined process, much like baking a cake. This process includes initialization, forking, file descriptor closure, and directory alteration, each step crucial for the daemon’s functionality.

Examples of daemons, like udev and crond, illustrate the diverse roles they play in computing. From managing device nodes to handling scheduled tasks, daemons perform a wide range of functions that keep our systems running smoothly.

In conclusion, daemons, though often unseen and underappreciated, are integral to the world of computing. They silently and efficiently manage tasks and services, making our digital lives smoother and more efficient. So, the next time your system boots up or your print job is processed, remember the silent engine powering your digital journey – the daemons!