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Full Discussion: Background Processes
Top Forums Shell Programming and Scripting Background Processes Post 302401427 by abubacker on Saturday 6th of March 2010 04:17:11 AM
Old 03-06-2010
MySQL Solution
If you want to run the process background programmatically , then you must make the process as a daemon.

I :

* The first step is that change the current directory as root "/" because it provide the
facility to do all the operation from the root
* If you want to mount a file system then you are unable to do this with out changing cur_dir into a root dir * what are all the path name you planned to give that should be in a absolute path name

II:

* Create a process and kill the parent of that process
* It will make the living process ( child ) as a child of init() and its process id will become 1
* Though a we never need a parent for a daemon

III :
* Daemon should be a session leader
* This can be achieved using setsid() in C

IV :
* We don't need an interaction of user for daemon process
* So we close all the descriptor
* We should assure that no other file descriptor would be assign for this process

V :
* Output and the monitoring the daemon will be done using a log files
* It is better to log the information in a /var/log/ directory structure
VI :
* Daemon should always in a running state
* So we should secure the daemon from the signals
* We should ignore all the signals except SIGHUP
* As a convention SIGHUP uses for reading configuration file
VII :
* Have a termination handler
* We should do some operation whenever we terminate the daemon
* Like releasing the memory closing the configuration file etc .




Here I provide an example code :
Code:
/* header files */
#include <stdio.h>
#include <ctype.h>
#include <signal.h>
#include <sys/wait.h>

/* Global variables */
...


/* Function prototypes: */
...
void terminate (int signum); /* clean up before termination */


int
main (void)
{
  ...

  if (chdir (ROOT_DIR))         /* change to directory containing data files */
   {
     fprintf (stderr, "`%s': ", ROOT_DIR);
     perror (NULL);
     exit (1);
   }

   /* Daemonize a process  */



   switch (fork ())
     {
     case -1:                    /* can't fork */
       perror ("fork()");
       exit (3);
     case 0:                     /* child, process becomes a daemon: */
       close (STDIN_FILENO);
       close (STDOUT_FILENO);
       close (STDERR_FILENO);
       if (setsid () == -1)      /* request a new session (job control) */
         {
           exit (4);
         }
       break;
     default:                    /* parent returns to calling process: */
       return 0;
     }

   /* Establish signal handler to clean up before termination: */



   if (signal (SIGTERM, terminate) == SIG_IGN)
     signal (SIGTERM, SIG_IGN);
   signal (SIGINT, SIG_IGN);
   signal (SIGHUP, SIG_IGN);

   /* Main program loop */
   /* Operation done here */

   while (keep_going)
     {
       ...
     }

   return 0;
}



/* Termination handler */

void  terminate (int signum)
{
  keep_going = 0;
  signal (signum, termination_handler);
}

 

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LEARN ABOUT DEBIAN

platform::shell

platform::shell(3tcl)					       Tcl Bundled Packages					     platform::shell(3tcl)

__________________________________________________________________________________________________________________________________________________

NAME

       platform::shell - System identification support code and utilities

SYNOPSIS

       package require platform::shell ?1.1.4?

       platform::shell::generic shell
       platform::shell::identify shell
       platform::shell::platform shell
_________________________________________________________________

DESCRIPTION

       The platform::shell package provides several utility commands useful for the identification of the architecture of a specific Tcl shell.

       This  package  allows the identification of the architecture of a specific Tcl shell different from the shell running the package. The only
       requirement is that the other shell (identified by its path), is actually executable on the current machine.

       While for most platform this means that the architecture of the interrogated shell is identical to the architecture of  the  running  shell
       this  is  not generally true. A counter example are all platforms which have 32 and 64 bit variants and where a 64bit system is able to run
       32bit code. For these running and interrogated shell may have different 32/64 bit settings and thus different identifiers.

       For applications like a code repository it is important to identify the architecture of the shell which will  actually  run  the  installed
       packages, versus the architecture of the shell running the repository software.

COMMANDS

       platform::shell::identify shell
	      This command does the same identification as platform::identify, for the specified Tcl shell, in contrast to the running shell.

       platform::shell::generic shell
	      This command does the same identification as platform::generic, for the specified Tcl shell, in contrast to the running shell.

       platform::shell::platform shell
	      This command returns the contents of tcl_platform(platform) for the specified Tcl shell.

KEYWORDS

       operating system, cpu architecture, platform, architecture

platform::shell 						       1.1.4						     platform::shell(3tcl)
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