How do I run my server as a daemon process?

For a few days I have been trying to run my server as a daemon process that runs continuously. Right now, my server closes the connection with the client and then closes itself. So I am able to send my packet once to the server, but when I try to send it again I get a segmentation fault error.

Also, even though I wrote the daemon process, I am not sure about its behavior and whether it is working or not.

Server Code:

#include <sys/socket.h>
#include <netinet/in.h>
#include "unistd.h"
#include <syslog.h>
#include <math.h>
#define MAXPROFILES  2

float Pearson(int mySum, int recSum, int multSum);

int main(int argc, char *argv[])
{
    int sockfd, newsockfd, portno, clilen;
    struct sockaddr_in serv_addr, cli_addr;
    unsigned char buf[1024];
    int myDataBinary[500] = {0};
    int myDataBinary2[500] = {0};
    int recData[500] = {0};*/
    int index1=0;

    struct profile_t
    {
        unsigned char length;
        unsigned char type;
        unsigned char *data;
    };

    typedef struct profile_datagram_t
    {
       unsigned char *src;
       unsigned char *dst;
       unsigned char ver;
       unsigned char n;
       struct profile_t profiles[MAXPROFILES];
    } header;


    header outObj;
    int j =0;
    int i =0;

    extern int daemon_proc;   /* defined in error.c */

    void daemon_init (const char *pname, int facility)
    {
   /* 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);
       }

         /* Close out the standard file descriptors */
          close(STDIN_FILENO);
          close(STDOUT_FILENO);
          close(STDERR_FILENO);

         /* Daemon-specific initialization goes here */

      }


         if (argc < 2) {
        fprintf(stderr,"usage: %s port_number1",argv[0]);
        exit(1);
     }
          sockfd = socket(AF_INET, SOCK_STREAM, 0);
          if (sockfd < 0)
          error("ERROR DETECTED !!! Problem in opening socket");

          bzero((char *) &serv_addr, sizeof(serv_addr));
          portno = atoi(argv[1]);

          serv_addr.sin_family = AF_INET;
          serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
          serv_addr.sin_开发者_开发知识库port = htons(portno);

          if (bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0)
          error("ERROR DETECTED !!! There was a problem in binding");

          listen(sockfd, 10);
          clilen = sizeof(cli_addr);

    while (1){

      printf("Server listening on port number %d...\n", serv_addr.sin_port);

      newsockfd = accept(sockfd,(struct sockaddr *) &cli_addr, &clilen);

      if (newsockfd < 0)
  error("ERROR DETECTED !!! the connection request was not accepted");

  int rc = read(newsockfd,buf,100);
  if(rc < 0){
     printf("error");
 }
 else {
     printf("success %d",rc);
 }


    outObj.src = malloc(4);
    outObj.dst = malloc(4);
            // printf(pointer);
             memcpy(outObj.src,buf+0,4);
             memcpy(outObj.dst,buf+4,4);
             memcpy(&outObj.ver,buf+8,1);
             memcpy(&outObj.n,buf+9,1);

 printf("\nSource IP = ");
 for(int i=0;i<4;i++){
     printf("%d ",outObj.src[i]);
 }

 printf("\nDestination IP = ");
  for(int i=0;i<4;i++){
     printf("%d ",outObj.dst[i]);
 }

 printf("\nVersion = %d",outObj.ver);
 printf("\nNumber of messages = %d",outObj.n);

 int k = 10;

 for(i=0;i<outObj.n;i++){
            memcpy(&outObj.profiles[i].length,buf+k,1);
            memcpy(&outObj.profiles[i].type,buf+k+1,1);
            outObj.profiles[i].data = malloc(outObj.profiles[i].length);
            memcpy(outObj.profiles[i].data,buf+k+2,5);
            k +=7;
}

for(int i=0;i<outObj.n;i++){
        printf("\n------- Message %d --------",i+1);
        printf("\nLength : %d",outObj.profiles[i].length);
        printf("\nType : %d\n",outObj.profiles[i].type);
        for(int j=0;j<5;j++){
            printf(" Data[%d] : %d",j,outObj.profiles[i].data[j]);
        }
    }

      float rho;

for(int i=0;i<outObj.n;i++){
    printf("\n\n---------- Values for Data Profile %d ------------",i+1);
    index1=0;
    int sumRecievedData = 0;
    int sumMyData = 0;
    int sumMultpliedData = 0;
    int my_data[10] = {0};//  = {1,2,3,4,5};
    int myDataBinary[500] = {0};
    int recData[500] = {0};


    if(i==0){
        my_data[0] = 1;
        my_data[1] = 3;
        my_data[2] = 9;
        my_data[3] = 10;
    } else if(i==1){
        my_data[0] = 1;
        my_data[1] = 2;
        my_data[2] = 3;
        my_data[3] = 4;
        my_data[4] = 5;
    }



    for(int i=0; i<sizeof(my_data)/sizeof(int);i++)
        {
            if(my_data[i] > 0){
                index1 = my_data[i];
                myDataBinary[index1] = 1;
                //printf("my data %d = %d\n",index1,myDataBinary[index1]);
            }
    }

    for (int j=0; j<outObj.profiles[i].length;j++) {

        if(outObj.profiles[i].data[j] > 0){
            index1 = outObj.profiles[i].data[j];
            recData[index1] = 1;
            //printf("rec data %d = %d\n",index1,recData[index1]);
        }
    }

    for(int i=0;i<500;i++){
        sumRecievedData += recData[i];
        sumMyData += myDataBinary[i];
        sumMultpliedData += recData[i] * myDataBinary[i];
    }

    printf("\nrecSum = %d, \nmySum = %d, \nmultSum = %d\n",sumRecievedData,sumMyData,sumMultpliedData);

    rho = Pearson(sumMyData,sumRecievedData,sumMultpliedData);
    printf("\nPearson Coefficient for Data Profile %d= %f\n",i+1,rho);
}


return 0;
   }
    //exit(EXIT_SUCCESS);
   }


float Pearson(int mySum, int recSum, int multSum)
{
float Cov =0;
float sdMyData = 0;
float sdRecievedData =0;
float rho;
int n = 500;

Cov = (1.0/(n-1))*(multSum - (1.0/n)*mySum*recSum);
sdMyData = sqrt((1.0/(n-1))*(mySum - (1.0/n)*mySum*mySum));
sdRecievedData = sqrt((1.0/(n-1))*(recSum - (1.0/n)*recSum*recSum));
printf("\nCovariance = %f, \nVarianceMyData = %f, \nVarianceRecData = %f",Cov,sdMyData,sdRecievedData);
if (sdMyData == 0.0 || sdRecievedData == 0.0){
    rho = 0.0;
}else{
    rho = Cov/(sdMyData*sdRecievedData);
}

return(rho);
}

The server does return(0); at the bottom of the supposedly infinite loop, thus exiting from main() and terminating.

As noted in a comment, your code includes a nested function daemon_init() which is never called. Nested functions are a GCC-only feature; you should avoid using them. If you do call it, the server is going to have problems because it closes stdout and stderr but your code then tries to write to the now closed files.

Without the client code, it is very far from clear what information is being sent over the wire. There is one read() call:

int rc = read(newsockfd,buf,100);

That should be using sizeof(buf) in place of 100; and it is wasteful to use char buf[1024]; when you only use 100 bytes. You check that you got some data; you do not check that you got all the data you expect. You might, therefore, be reading uninitialized data.

There are numerous other similar problems in the code, especially with constants used somewhat inappropriately. As also noted in a comment, the code is not properly modularized.

The code does not seem to respond to the client; its outputs only go to its standard output (or error).

This code compiles reasonably cleanly, but still doesn't call daemon_init() for the reasons mentioned earlier.

#include <errno.h>
#include <math.h>
#include <netinet/in.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>     /* exit() */
#include <string.h>
#include <sys/socket.h>
#include <sys/stat.h>   /* umask() */
#include <syslog.h>
#include <unistd.h>

#define MAXPROFILES  2

static void error(const char *fmt, ...)
{
    va_list args;
    int errnum = errno;
    va_start(args, fmt);
    vfprintf(stderr, fmt, args);
    va_end(args);
    fprintf(stderr, ": %d %s\n", errnum, strerror(errnum));
    exit(1);
}

static float Pearson(int mySum, int recSum, int multSum);

static void daemon_init(void)
{
    /* Our process ID and Session ID */
    pid_t pid, sid;

    /* Fork off the parent process */
    pid = fork();
    if (pid < 0)
        error("failed to fork");

    /* 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)
        error("failed to set session ID");

    /* Change the current working directory */
    if ((chdir("/")) < 0)
        error("failed to chdir to root");

    /* Close out the standard file descriptors */
    close(STDIN_FILENO);
    close(STDOUT_FILENO);
    close(STDERR_FILENO);

    /* Daemon-specific initialization goes here */
}

int main(int argc, char *argv[])
{
    int sockfd, newsockfd, portno;
    socklen_t clilen;
    struct sockaddr_in serv_addr, cli_addr;
    unsigned char buf[1024];

    struct profile_t
    {
        unsigned char length;
        unsigned char type;
        unsigned char *data;
    };

    typedef struct profile_datagram_t
    {
        unsigned char *src;
        unsigned char *dst;
        unsigned char ver;
        unsigned char n;
        struct profile_t profiles[MAXPROFILES];
    } header;

    header outObj;

    if (argc != 2)
        error("usage: %s port", argv[0]);
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0)
        error("ERROR DETECTED !!! Problem in opening socket");

    bzero((char *) &serv_addr, sizeof(serv_addr));
    portno = atoi(argv[1]);

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    serv_addr.sin_port = htons(portno);

    if (bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0)
        error("ERROR DETECTED !!! There was a problem in binding");

    listen(sockfd, 10);

    while (1)
    {
        clilen = sizeof(cli_addr);
        printf("Server listening on port number %d...\n", serv_addr.sin_port);
        newsockfd = accept(sockfd, (struct sockaddr *)&cli_addr, &clilen);

        if (newsockfd < 0)
            error("ERROR DETECTED !!! the connection request was not accepted");

        int rc = read(newsockfd,buf,100);
        if (rc < 0)
            error("read error");
        else
            printf("read: success %d", rc);

        outObj.src = malloc(4);
        outObj.dst = malloc(4);
        // printf(pointer);
        memcpy(outObj.src,buf+0,4);
        memcpy(outObj.dst,buf+4,4);
        memcpy(&outObj.ver,buf+8,1);
        memcpy(&outObj.n,buf+9,1);

        printf("\nSource IP = ");
        for (int i=0;i<4;i++)
            printf("%d ",outObj.src[i]);

        printf("\nDestination IP = ");
        for (int i=0;i<4;i++)
            printf("%d ",outObj.dst[i]);

        printf("\nVersion = %d",outObj.ver);
        printf("\nNumber of messages = %d",outObj.n);

        int k = 10;

        for (int i=0;i<outObj.n;i++)
        {
            memcpy(&outObj.profiles[i].length,buf+k,1);
            memcpy(&outObj.profiles[i].type,buf+k+1,1);
            outObj.profiles[i].data = malloc(outObj.profiles[i].length);
            memcpy(outObj.profiles[i].data,buf+k+2,5);
            k +=7;
        }

        for (int i=0;i<outObj.n;i++)
        {
            printf("\n------- Message %d --------",i+1);
            printf("\nLength : %d",outObj.profiles[i].length);
            printf("\nType : %d\n",outObj.profiles[i].type);
            for (int j=0;j<5;j++)
            {
                printf(" Data[%d] : %d",j,outObj.profiles[i].data[j]);
            }
        }

        for (int i=0;i<outObj.n;i++)
        {
            printf("\n\n---------- Values for Data Profile %d ------------",i+1);
            int index1=0;
            int sumReceivedData = 0;
            int sumMyData = 0;
            int sumMultpliedData = 0;
            int my_data[10] = {0};
            int myDataBinary[500] = {0};
            int recData[500] = {0};

            if (i==0)
            {
                my_data[0] = 1;
                my_data[1] = 3;
                my_data[2] = 9;
                my_data[3] = 10;
            }
            else if (i==1)
            {
                my_data[0] = 1;
                my_data[1] = 2;
                my_data[2] = 3;
                my_data[3] = 4;
                my_data[4] = 5;
            }

            for (int i=0; i<sizeof(my_data)/sizeof(int);i++)
            {
                if (my_data[i] > 0)
                {
                    index1 = my_data[i];
                    myDataBinary[index1] = 1;
                    //printf("my data %d = %d\n",index1,myDataBinary[index1]);
                }
            }

            for (int j=0; j<outObj.profiles[i].length;j++)
            { 
                if (outObj.profiles[i].data[j] > 0)
                {
                    index1 = outObj.profiles[i].data[j];
                    recData[index1] = 1;
                    //printf("rec data %d = %d\n",index1,recData[index1]);
                }
            }

            for (int i=0;i<500;i++)
            {
                sumReceivedData += recData[i];
                sumMyData += myDataBinary[i];
                sumMultpliedData += recData[i] * myDataBinary[i];
            }

            printf("\nrecSum = %d, \nmySum = %d, \nmultSum = %d\n",sumReceivedData,sumMyData,sumMultpliedData);

            float rho = Pearson(sumMyData,sumReceivedData,sumMultpliedData);
            printf("\nPearson Coefficient for Data Profile %d= %f\n",i+1,rho);
        }

        return 0;
    }
    //exit(EXIT_SUCCESS);
}

static float Pearson(int mySum, int recSum, int multSum)
{
    float Cov =0;
    float sdMyData = 0;
    float sdReceivedData =0;
    float rho;
    int n = 500;

    Cov = (1.0/(n-1))*(multSum - (1.0/n)*mySum*recSum);
    sdMyData = sqrt((1.0/(n-1))*(mySum - (1.0/n)*mySum*mySum));
    sdReceivedData = sqrt((1.0/(n-1))*(recSum - (1.0/n)*recSum*recSum));
    printf("Covariance = %f\n",Cov);
    printf("VarianceMyData = %f\n",sdMyData);
    printf("VarianceRecData = %f\n",sdReceivedData);
    if (sdMyData == 0.0 || sdReceivedData == 0.0)
        rho = 0.0;
    else
        rho = Cov/(sdMyData*sdReceivedData);

    return(rho);
}

It still needs a lot of work.