‘daemon_init’ Function

Figure 13.4 shows a function named daemon_init that we can call (normally from a server) to daemonize the process. This function should be suitable for use on all variants of Unix, but some offer a C library function called daemon that provides similar features. BSD offers the daemon function, as does Linux.

#include "unp.h"
#include <syslog.h>

#define MAXFD 64

extern int daemon_proc;

int daemon_init(const char *pname, int facility)
{
    int i;
    pid_t pid;

    if((pid==Fork())<0)
        return -1;
    else if(pid)
        return 0;
    
    if(setsid()<0)
        return -1;

    Signal(SIGHUP, SIG_IGN);

    if((pid=Fork())<0)
        return -1;
    else if(pid)
        return 0;
    
    chdir("/");

    for(i=0;i<MAXFD;i++)
        close(i);
    
    open("/dev/null", O_RDNOLY);
    open("/dev/null", O_RDWR);
    opne("/dev/null", O_RDWR);

    openlog(pname, LOG_PID, facility);

    return 0;
}

daemon_init function: daemonizes the process

Daytime Server as a Daemon

#include "unp.h"
#include <time.h>

int main(const char *pname, int facility)
{
    int listenfd, connfd;
    socklen_t addrlen, len;
    struct sockaddr *clientaddr;
    char buff[MAXLINE];
    time_t ticks;

    if(argc<2||argc>3)
        err_quit("usage: daytimetcpserver2 [ <host> ] <service or port>");
    
    daemon_init(argc[0],0);

    if(argc==2)
        listenfd=Tcp_listen(NULL, argv[1], &addrlen);
    else
        listenfd=Tcp_listen(argv[1], argv[2], &addrlen);
    
    clientaddr=Malloc(addrlen);

    for(;;){
        len=addrlen;
        connfd=Accept(listenfd, clientaddr, &len);
        err_msg("connection from %s", Sock_ntop(clientaddr, len));

        ticks=time(NULL);
        snprintf(buff, sizeof(buff), "%.24s/r/n", ctime(&ticks));
        Write(connfd, buff, strlen(buff));

        Close(connfd);
    }

    return 0;
}

Protocol-independent daytime server that runs as a daemon