Question

I read about Daemon Programming and i think I’ll be needing this to detect my devices if online or not eg(RS232, usb, ethernet). then fetch in a webservice PHP.

The code from this site. http://www.netzmafia.de/skripten/unix/linux-daemon-howto.html

I added some parts to test if i can detect devices.

#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>
#include <syslog.h>
#include <string.h>
int devfd;
int main(int argc, char *argv[]) {

        int c;


        while((c=getopt(argc,argv,"s")) != -1)
            switch(c){

            case 's': devfd = open("/dev/ttyUSB0", O_RDWR);
                        if(devfd==-1){
                        printf("offline\n");
                        }
                        else{
                        printf("online\n");
                        }
                        break;
            default: printf("Wrong command\n");

            }

        /* Our process ID and Session ID */
        pid_t pid, sid;

        /* Fork off the parent process */
        pid = fork();
        if (pid < 0) {
                exit(EXIT_FAILURE);
        }
        /* If we got a good PID, then
           we can exit the parent process. */
        if (pid > 0) {
                exit(EXIT_SUCCESS);
        }

        /* Change the file mode mask */
        umask(0);

        /* Open any logs here */        

        /* Create a new SID for the child process */
        sid = setsid();
        if (sid < 0) {
                /* Log the failure */
                exit(EXIT_FAILURE);
        }



        /* Change the current working directory */
        if ((chdir("/")) < 0) {
                /* Log the failure */
                exit(EXIT_FAILURE);
        }



        /* Daemon-specific initialization goes here */

        /* The Big Loop */
        while (1) {



        }
   exit(EXIT_SUCCESS);
}

I added this code..

while((c=getopt(argc,argv,"s")) != -1)
            switch(c){

            case 's': devfd = open("/dev/ttyUSB0", O_RDWR);
                        if(devfd==-1){
                        printf("offline\n");
                        }
                        else{
                        printf("online\n");
                        }
                        break;
            default: printf("Wrong command\n");

            }

so doing it like this in the terminal.

./daemon -s //prints offline because the device USB0 is not connected.

Is there another way for me to detect my devices?

Thanks,

Answer 1

If it has udev, you can use libudev to detect and monitor your devices. Checkout nice tutorial from signal11.