Listing 1 The main() function

1: #include <stdio.h>
2: #include <unistd.h>
3:
4: /* These files are listed later in this article: */
5: #include "lst03.c"
6: #include "lst02.c"
7:
8: int main()
9: {
10:    /* The variable pid will hold the pid returned by fork(). */
11:    int pid;
12:
13:    /* Use fork() to create an exact copy of this process: */
14:    pid = fork();
15:
16:    /* If fork() return -1, something went wrong. */
17:    if( pid == -1 )
18:    {
19:        /* Output the error to STDOUT: */
20:        perror( "fork error" );
21:        /* And exit: */
22:        exit(1);
23:    }
24:
25:    /*
26:     * If fork() returned 0, we're in the child. By using
27:     * the child, we make sure we're not a process group
28:     * leader, and that we're disconnected from the controlling
29:     * terminal.
30:    */
31:    if( pid == 0 )
32:    {
33:        /*
34:         * We use setsid() to create a new session, this works
35:         * only if the process is not a process group leader.
36:         * Since we're executing in the child here, and a child-
37:         * process can never be a process group leader, we can
38:         * be sure setsid() will be successful:
39:        */
40:        setsid();
41:
42:        /*
43:         * Here, we close STDIN, STDOUT and STERR. The whole idea
44:         * with daemons is that they should just lay in the back-
45:         * ground doing their job, without making any noise. So,
46:         * this daemon will not read nor write any information from
47:         * or to the terminal.
48:        */
49:        close( STDIN_FILENO );
50:        close( STDOUT_FILENO );
51:        close( STDERR_FILENO );
52:
53:        /*
54:         * Next thing we do is to change the working directory
55:         * to /. This is to make sure the daemon is not making
56:         * any device busy that you might want to unmount.
57:        */
58:        chdir( "/" );
59:
60:        /*
61:         * So, we've finally become a daemon, so we're ready to
62:         * start the infinite-loop:
63:        */
64:        while(1)
65:        {
66:            /* This function will take care of all the quota-stuff: */
67:            do_quota_stuff();
68:
69:            /*
70:             * Sleep for a couple of seconds before we perform all
71:             * quota-stuff again:
72:            */
73:            sleep(2);
74:        }
75:    }
76:
77:    /* Everything went fine, so we'll return 0: */
78:    return 0;
79: }