Writing a Simple Linux Daemon Program

by David Loo | Jul 15, 2012 | Android, Linux Development

I have decided to write a watcher daemon to watch a specified folder for any newly created files or folders. I did some googling and found that it was very simple to create a daemon program in Linux.

First you will need to create your source file and include the following header file:

#include <unistd.h>

In the main function you need to call daemon() like this:

int main()
{
    if (daemon(0,0) == -1)
         err(1, NULL);
    while(1)
    {
         Do something here....
    }
}

In the while loop you can put your own code to perform a specific task. 

To run the daemon when your system boots up edit the file /etc/init.d/rc.local and add the following line at the end of the file:

/usr/sbin/yourdaemon

note: make sure the you copied the file to /usr/sbin or else the file can not be found when the system is booting up.

The daemon function parameters, I have specifice 0 for the first paramter to use the root “/” folder instead of the working folder and the second parameter I have done the same which will redirect all standard input, output and errors to /dev/null.

Detailed information on how to use the daemon function can be found here.