daemon

become_daemon.h

/***become_daemon.h***/
#ifndef __BECOME_DAEMON_H__
#define __BECOME_DAEMON_H__

#define BD_NO_CHDIR           01   /*Don't chdir("/")*/
#define BD_NO_CLOSE_FILES     02   /*Don't close all open files*/
#define BD_NO_REOPEN_STD_FDS  04   /*Don't reopen stdin, stdout, and stderr to /dev/null*/
#define BD_NO_UNMASK          010  /*Don't do a unmask(0)*/
#define BD_MAX_CLOSE          8192 /*Maximum file descriptors to close if sysconf(_SC_OPEN_MAX) is
                        indeterminate*/
int becomeDaemon(int flags);

#endif

become_daemon.c

/*become_daemon.c*/
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include "become_daemon.h"

int becomeDamon(int flags)
{
        int maxfd, fd;
        switch(fork()) {
        case -1:
            return -1;
        case 0:
            break;
        default:
            _exit(0);
        }

    if(setsid() < 0) {
        printf("setsid error\n");
        return -1;
    }

    switch(fork()) {
        case -1:
            return -1;
        case 0:
            break;
        default:
            _exit(0);
    }

    if(!(flags && BD_NO_UNMASK)) {
        umask(0);
    }

    if(!(flags && BD_NO_CHDIR)) {
        chdir("/");
    }

    if(!(flags && BD_NO_CLOSE_FILES)) {
        maxfd = sysconf(_SC_OPEN_MAX);
        printf("maxfd = %d,BD_MAX_CLOSE=%d\n",maxfd,BD_MAX_CLOSE);
        if(maxfd == -1)
            maxfd = BD_MAX_CLOSE;
        for(fd = 0; fd < maxfd; fd++)
            close(fd);
    }

    if(!(flags && BD_NO_REOPEN_STD_FDS)) {
        close(STDIN_FILENO);

        fd = open("/dev/null", O_RDWR);
        if(fd != STDIN_FILENO)
            return -1;
        if(dup2(fd,STDOUT_FILENO) != STDOUT_FILENO)
            return -1;
        if(dup2(fd,STDERR_FILENO) != STDERR_FILENO)
            return -1;
    }
    return 0;
}

deamon_case.c

/**deamon_case.c**/
#include "become_daemon.h"
#include <stdio.h>
#include <unistd.h>

int main(int argc, char *argv[])
{
    becomeDamon(0);
    sleep(100);
    return 0;
}

编译运行：

[root@localhost 37_daemon]# gcc -g become_daemon.c deamon_case.c -o daemon
[root@localhost 37_daemon]# ./daemon
maxfd = 1024,BD_MAX_CLOSE=8192
[root@localhost 37_daemon]# ps -ef | grep daemon
dbus      3054     1  0 10:13 ? 00:00:02 dbus-daemon --system
xfs       3384     1  0 10:13 ? 00:00:00 xfs -droppriv -daemon
avahi     3428     1  3 10:13 ? 00:14:34 avahi-daemon: running [localhost.local]
avahi     3429  3428  0 10:13 ? 00:00:00 avahi-daemon: chroot helper
root      3507     1  0 10:13 ? 00:00:00 /usr/sbin/gdm-binary -nodaemon
root      3544  3507  0 10:13 ? 00:00:00 /usr/sbin/gdm-binary -nodaemon
root      4025     1  0 10:38 ? 00:00:00 /bin/dbus-daemon --fork --print-pid 4 --print-address 6 --session
root      4035     1  0 10:38 ? 00:00:00 /usr/bin/gnome-keyring-daemon
root      4037     1  0 10:38 ? 00:00:00 /usr/libexec/gnome-settings-daemon
root      4070     1  0 10:38 ? 00:00:00 /usr/libexec/gnome-vfs-daemon
root      4142     1  0 10:38 ? 00:00:00 /usr/libexec/mapping-daemon
root     19840     1  0 17:15 ? 00:00:00 ./daemon
root     19842 19657  0 17:15 pts/2    00:00:00 grep daemon
[root@localhost 37_daemon]# ps -C daemon -o "pid ppid pgid sid tty command"
  PID  PPID  PGID   SID TT       COMMAND
19840     1 19839 19839 ? ./daemon
[root@localhost 37_daemon]#