How to Create a Daemon on Linux
Daemons are background processes that run on a server or system without interacting with users or requiring user intervention. They are essential to the functioning of Linux systems, enabling essential system tasks and services to operate in the background, even when there are no users logged in. Creating a daemon can be an important skill for system administrators and developers alike. In this article, we will outline the steps for creating a daemon on Linux.
Step 1: Develop your Daemon Code
Before creating a daemon, you need to write the code to define the behavior of the daemon. Your daemon code should be designed to operate in the background and perform a task that runs continuously without user intervention. Some examples of daemon code include monitoring a system or a set of files, handling daemons or processes, or performing routine system cleanup tasks.
Step 2: Include Necessary Headers and Libraries
Once you have developed your daemon code, you need to include the necessary headers and libraries that the code requires. These may include the standard library (stdlib.h), file operations library (stdio.h), process control library (unistd.h), and daemon library (sys/daemon.h), among others. If you are not familiar with the headers and libraries that your code requires, consult your programming language documentation, Linux operating system documentation or seek the assistance of a developer.
Step 3: Prepare your Daemon for Launch
Before launching your daemon, there are several important steps you need to complete to prepare your daemon process. First, you need to create a daemon process group using the setsid() command. This detaches the daemon process from the controlling terminal and creates a new session group for the daemon. Then, you need to fork your daemon process and exit the parent process. This ensures that the daemon runs independently of the parent process.
Step 4: Set Signal Handling
By default, daemons are signaled when the system receives an interrupt signal (SIGINT), a quit signal (SIGQUIT), or a terminate signal (SIGTERM). However, if your daemon code requires handling other signals, you can use the signal handling function to specify different actions to be taken when specific signals are received.
Step 5: Implement your Daemon Code
Now that you have set up the initial conditions for your daemon process, it is time to implement your daemon code. This typically involves an infinite loop that runs continuously, performing the desired task over and over, without needing to be restarted.
Step 6: Launch your Daemon Process
Finally, to launch your daemon process, you will need to compile your code into a binary executable and launch the daemon by typing the daemon’s name at the command line. This will start the daemon in the background, running continuously, until it is shut down or the system is rebooted.