Daemon and daemon output

1 Creating an output program2 Creating a daemon
1 Creating an output daemon does not contact the terminal, so you need to create another program for the output. You can also use/bin/echo directly
-----example_daemon_help.cc

#include <stdio.h>int main (int argc, char** argv) {     if (argc = = 1)     {          printf ("only one parameter \ n"); 
   }     Else if (argc = = 2)     {          printf ("%s \ n", argv[1]);     }     else     {          printf ("too more parameter:%d\n", argc);     }     return 0;}

Compile:
g++-o example_daemon_help example_daemon_help.cc--std=c++11
2 Creating a Daemon
Write a function First: int daemon_init (const char* pname, int facility), and then, as soon as the process name is passed into this function, it becomes the daemon.
-----from the 13th chapter of UNP, with changes

int Daemon_init (const char* pname, int facility) {umask (0);     pid_t pid;     if (PID = fork ()) < 0) return-1; else if (PID > 0) _exit (0);      Parent terminates//child 1 continues//become session leader if (Setsid () < 0) return-1;     Ignore SIGHUP//Signal (SIGHUP, sig_ign);     struct Sigaction sa;     Sa.sa_handler = sig_ign;     Sigemptyset (&sa.sa_mask);     sa.sa_flags = 0;     if (Sigaction (SIGHUP, &sa, nullptr) < 0) _exit (0);     if (PID = fork ()) < 0) return-1;     else if (PID > 0) _exit (0);     Child 1 terminates//child 2 continues helpguy::d aemon_flag = 1;     Changes working directory ChDir ("/");     Close off file descriptors Rlimit RL;     if (Getrlimit (Rlimit_nofile, &AMP;RL) < 0) return-1; int Fdmax = Rl.rlim_max = = rlim_infinity?     1024:rl.rlim_max;     for (int i = 0; i < Fdmax; ++i) Close (i);REDIRECT stdin, stdout and stderr to/dev/null open ("/dev/null", o_rdonly);     Open ("/dev/null", O_RDWR);     Open ("/dev/null", O_RDWR);     Openlog (PName, log_pid, facility); return 0;}

About _exit See: http://blog.csdn.net/alex_my/article/details/39318607
Here is the entire program code:
-----example_daemon.cc

#include "helpguy.h"  //contains Daemon_init function # include <syslog.h>int main (int argc, char** argv) {     //daemon Process     Daemon_init (argv[0], 0);     int count = 0;     while (++count <= 2)     {          sleep (3);                   Notifice          pid_t pid;          if (PID = fork ()) = = 0)          {               ///child process inherits the parent process's file descriptor               //In Daemon_init, the parent process's stdout is redirected to/dev/null               close (1);               Open ("/dev/pts/0", o_wronly);                             EXEC               execl ("/home/alex_my/code/unp/example_daemon_help", "Example_daemon_help", "3 sec Now", nullptr);               You can also use this               //execl ("/bin/echo", "echo", "Clock 3", nullptr);          }                   Parent          waitpid (PID, nullptr, 0);     }     return 0;}

Daemon_init can be placed in this file. Compilation: g++-o example_daemon example_daemon.cc--std=c++11
There is use to nullptr, so add--std=c++11, note that the equal sign does not have spaces on either side
I put it in the static library file of Libhelpguy.a. Compilation: g++-O example_daemon example_daemon.cc-l.-lhelpguy--std=c++11
About creating a static library see http://blog.csdn.net/alex_my/article/details/43529323

About EXECL See: http://blog.csdn.net/alex_my/article/details/39374447

Daemon and daemon output