Background programming in C

Question

I'm trying to create a background program that has main config file which contains another config file locations and execute each of them. For example: if main_config.conf:

/home/conf1
/home/conf2

i want to execute ./background_pro /home/conf1 and ./background_pro /home/conf2 in background. How do i do that ? I'm using below structure.Thank you

#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>
#include <syslog.h>
#include <string.h>

int main(void) {

        /* Our process ID and Session ID */
        pid_t pid, sid;

        /* Fork off the parent process */
        pid = fork();
        if (pid < 0) {
                exit(EXIT_FAILURE);
        }
        /* If we got a good PID, then
           we can exit the parent process. */
        if (pid > 0) {
                exit(EXIT_SUCCESS);
        }

        /* Change the file mode mask */
        umask(0);

        /* Open any logs here */        

        /* Create a new SID for the child process */
        sid = setsid();
        if (sid < 0) {
                /* Log the failure */
                exit(EXIT_FAILURE);
        }



        /* Change the current working directory */
        if ((chdir("/")) < 0) {
                /* Log the failure */
                exit(EXIT_FAILURE);
        }

        /* Close out the standard file descriptors */
        close(STDIN_FILENO);
        close(STDOUT_FILENO);
        close(STDERR_FILENO);

        /* Daemon-specific initialization goes here */

        /* The Big Loop */
        while (1) {
           /* Do some task here ... */

           sleep(30); /* wait 30 seconds */
        }
   exit(EXIT_SUCCESS);
}

After closing the standard descriptors you should probably open them on `/dev/null`, since some library functions may expect them to be open. — Barmar, May 25 '15 at 22:48
You need to change the arguments to `main` to be `int argc, char*argv[]` so you can read the filename argument with the config file. — Barmar, May 25 '15 at 22:50
@iharob how to execute program multiple times with different arguments(argv) from daemon ? — Odko, May 25 '15 at 22:51
@akiD I am sorry it's still unclear, why would you execute it multiple times with different arguments? does it have to fork and execute itself? what are you trying to do? — Iharob Al Asimi, May 25 '15 at 22:54
@Barmar Thanks, how do i execute multiple times with arguments from daemon ? — Odko, May 25 '15 at 22:56
I don't understand your problem. You just type the command from the shell prompt multiple times, and give it different command line arguments. The "Daemon-specific initialization" code should open the file and read the configuration options from there. — Barmar, May 25 '15 at 23:01
Sorry about my english :) I want to make a child process for each arguments :) — Odko, May 25 '15 at 23:03
@Barmar can i make that program execute once command from shell prompt and make that program execute multiple times ?. if i execute `./daemon` it executes `./program conf1` `./program conf2` :) — Odko, May 25 '15 at 23:08
`./daemon` can be a shell script that executes those two commands. — Barmar, May 25 '15 at 23:17
Thanks for your time :) Looks like this was a stupid question :) I thought i could make c program that makes child processes and executes itself multiple times other than shell script :). — Odko, May 25 '15 at 23:21
Just run them one after the other. They'll run simultaneously because each of them puts itself in the background. — Barmar, May 26 '15 at 06:11
I'm assuming that `./program` is the program you showed in the question. — Barmar, May 26 '15 at 06:12

Hank Chang · Accepted Answer · 2015-05-29T08:28:40.643

1

Just append an '&' at the rear of shell command, then the command will run in background. I think, this may be what you want: daemon.bash

#!bash

# to stop a sub process
if [ "x$1" = "x-stop" ]; then
    if [ "x$2" = "xsub1" ]; then
        kill `cat sub1.pid`
    elif [ "x$2" = "xsub2" ]; then
        kill `cat sub2.pid`
    fi
    exit
fi

# to start sub processes
conf1=`head -1 main_config.conf`
conf2=`head -2 main_config.conf | tail -1`
nohup ./background_pro $conf1 &
pid1=$!
echo "$pid1" > sub1.pid
nohup ./background_pro $conf2 &
pid2=$!
echo "$pid2" > sub2.pid

Run the demon:

nohup ./daemon.bash &

The nohup will keep the program running even you turn off the terminal.

Stop sub process 1:

./daemon.bash -stop sub1

edited May 29 '15 at 08:28

answered May 26 '15 at 04:19

Hank Chang

199
2
10

http://pastebin.com/FMziPP4k is it right ? when i try `./script start &` it outputs http://pastebin.com/NYup97BM – Odko May 26 '15 at 05:40
and how to add stop case in script ? – Odko May 26 '15 at 05:54
Is it running simultaneously ? – Odko May 26 '15 at 06:03
The backquote (\`) means execute the command inside the backquotes and get the result as a variable. Why do you write `authlog.conf /var/log/auth.log`? – Hank Chang May 26 '15 at 06:48
Any program can run as deamon with nohup and '&' mark without special 'daemon code'. – Hank Chang May 26 '15 at 06:50
The '&' mark will let the programs in background simultaneously. – Hank Chang May 26 '15 at 06:51
The way to stop the daemom is `kill` the process, it need the process ID of running daemon. That's a complex problem. – Hank Chang May 26 '15 at 06:55
it's creating seperate process ids, is it possible to run it with one pid ? – Odko May 29 '15 at 03:30
It is not possible to run with one PID by this shell program. Only multi-thread programming can run in one PID. You may reference : http://www.yolinux.com/TUTORIALS/LinuxTutorialPosixThreads.html – Hank Chang May 29 '15 at 07:53
@akiD, Ok, I enhanced the shell script to be able to stop sub processes. – Hank Chang May 29 '15 at 08:29

score 0 · Answer 2 · edited May 23 '17 at 12:30

0

A background program might be what linux users call a "Daemon" program. Please look here on Creating a daemon in Linux where you can find a plethora of information on how to begin writing your own Daemon. For parsing command line arguments, i recommend reading the GNU c library manual for getopt().

edited May 23 '17 at 12:30

Community

1
1

answered May 26 '15 at 04:31

JD_GRINDER

344
2
6

Background programming in C

2 Answers2