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# 1  
Old 04-08-2009
Help with task daemon
believe it or not but this is my first c program (i've worked with java, C#, php though) I am trying to make a daemon that checks if mplayer is running(it's for a projection room) and if it is not then to run mplayer with a file.. So far it's not working and I don't know why

Help and comments would be appreciated
Code:
#include <sys/types.h>  /* include this before any other sys headers */ 
#include <sys/wait.h>   /* header for waitpid() and various macros */ 
#include <signal.h>     /* header for signal functions */ 
#include <stdio.h>      /* header for fprintf() */ 
#include <unistd.h>     /* header for fork() */ 
 
void  ChildProcess(void);                /* child process prototype  */ 
void  ParentProcess(void);               /* parent process prototype */
 
int  main(void) 
{     pid_t pid;

    while(1){ 
            int rc;
            rc<<system("ps ux | awk '/mplayer/ && !/awk/ {print $2}'"); 
          rc = WEXITSTATUS(rc); /* Check if mplayer is running */ 
       if(rc >= 0 ){ 
              pid = fork(); 
              if(pid>=0){     
                if (pid == 0)  
                 ChildProcess(); 
                else  
                 ParentProcess(); 
                } 
              } 
       else 
          {/*fork error*/}
   
     }
return (0); 
} 
 
void  ChildProcess(void) 
{ 
     execvp("mplayer ~/test.avi",NULL); 
     exit(0); 
} 
 
void  ParentProcess(void) 
{ 
    sleep(2); 
    return; 
}

# 2  
Old 04-08-2009
Quote:
Originally Posted by james2432
believe it or not but this is my first c program
I do
Quote:
Originally Posted by james2432
I am trying to make a daemon that checks if mplayer is running (it's for a projection room) and if it is not then to run mplayer with a file..
Not exactly what a daemon is for IMO, but that's not for here to discuss
Quote:
Originally Posted by james2432
So far it's not working and I don't know why
What exactly isn't working. I found a few things that might cause problems, but that could or couldn't be what you're looking for.
Code:
#include <sys/types.h>  /* include this before any other sys headers */ 
#include <sys/wait.h>   /* header for waitpid() and various macros */ 
#include <signal.h>     /* header for signal functions */ 
#include <stdio.h>      /* header for fprintf() */ 
#include <unistd.h>     /* header for fork() */ 
 
void  ChildProcess(void);                /* child process prototype  */ 
void  ParentProcess(void);               /* parent process prototype */
 
int  main(void) 
{     pid_t pid;

    while(1){ 
            int rc;
            // I don't think this is standard C behaviour, execpt if you want to
            // bit-shift left an uninitialized variable
            rc<<system("ps ux | awk '/mplayer/ && !/awk/ {print $2}'"); 
            [color=blue]// Where did that come from?
          rc = WEXITSTATUS(rc); /* Check if mplayer is running */ 
       if(rc >= 0 ){ 
              pid = fork();
              if(pid>=0){     
                if (pid == 0)  
                 ChildProcess(); 
                else  
                 ParentProcess(); 
                } 
              } 
       else 
          {/*fork error*/}
   
     }
return (0); 
} 
 
void  ChildProcess(void) 
{ 
     execvp("mplayer ~/test.avi",NULL); 
     exit(0); 
} 
 
void  ParentProcess(void) 
{ 
    sleep(2); 
    return; 
}

As a guideline, a daemon usually has this workflow:
Code:
initialize
pid=fork
if(pid==0)
    exit //parent
else
    while(1)
        do something

Your code, OTOH, never goes into background, and, in case mplayer keeps on crashing, will waste quite some time on process creation.
In your ChildProcess() function you could replace the execvp/exit combination with a simple exec, as this will replace the current process image (that of the child) with that of the program you're specifying.
# 3  
Old 04-08-2009
Code:
while(1){ 
            int rc;
            rc=system("ps ux | awk '/mplayer/ && !/awk/ {print $2}'"); 
          rc = WEXITSTATUS(rc); /* Check if mplayer is running */ 
       if(rc > 0 ){
              printf("i was here");
                 printf(rc); 
              pid = fork(); 
              if(pid>=0){     
                if (pid == 0)  
                 ChildProcess(); 
                else  
                 ParentProcess(); 
                } 
              }

It never gets to "i was here"
i'm trying to get the process ID so I can check if it is running then relaunch it...right now it just doesn't launch anything. and for the daemon part, I am aware that it's not reall daemonesk but I want to be able to stop it
# 4  
Old 04-08-2009
Code:
while(1){ 
            int rc;
            rc=system("ps ux | awk '/mplayer/ && !/awk/ {print $2}'"); 
          rc = WEXITSTATUS(rc); /* Check if mplayer is running */
            printf("I was here pid: %s\n",rc);

the output is always : I was here pid: (null)

*edit*
I was trying to fallow the example here:
http://joekuan.wordpress.com/2009/02...he-ps-command/
Last edited by james2432; 04-08-2009 at 11:48 PM..
# 5  
Old 04-09-2009
From the man-page of wait(2) (where WEXITSTATUS() is explained):
Quote:
WEXITSTATUS(status)
returns the exit status of the child. This consists of the least significant 16-8 bits of the status argument that the child specified in a call to exit() or _exit() or as the argument for a return statement in main(). This macro should only be employed if WIFEXITED returned true.
And I guess using %d instead of %s would be better in the printf statement, as it's an int, not a char*.
# 6  
Old 04-09-2009
Thanks for the help i was tired(i program all day long) and facepalmed when you mentioned the %d for decimal... i should have known

everything is sort of working mplayer never quits now :P
Code:
    while(1){ 
          int rc=system("ps -C mplayer -opid=");
                 
          rc = WEXITSTATUS(rc); /* Check if mplayer is running */
            printf("I was here pid: %d\n",rc); 
       if(rc > 0 ){
               
              pid = fork(); 
              if(pid>=0){     
                if (pid == 0)  
                 ChildProcess(); 
                else  
                 ParentProcess(); 
                } 
              } 
       else 
          {/*fork error*/}
   
     }
return (0); 
} 
 
void  ChildProcess(void) 
{ 
     system("mplayer ~/test.avi"); 
     exit(0); 
} 
 
void  ParentProcess(void) 
{ 
    sleep(2); 
    return; 
}

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