Question

I can compile this program which was provided to me, but that I must further develop. I have some questions about it:

#include <sys/types.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>

#define TIMEOUT (20)

int main(int argc, char *argv[])
{
  pid_t pid;
  if(argc > 1 && strncmp(argv[1], "-help", strlen(argv[1])) == 0)
    {
      fprintf(stderr, "Usage: RunSafe Prog [CommandLineArgs]\n\nRunSafe takes as arguments:\nthe program to be run (Prog) and its command line arguments (CommandLineArgs) (if any)\n\nRunSafe will execute Prog with its command line arguments and\nterminate it and any remaining childprocesses after %d seconds\n", TIMEOUT);
      exit(0);
    }

  if((pid = fork()) == 0)        /* Fork off child */
    {
      execvp(argv[1], argv+1);
      fprintf(stderr,"RunSafe failed to execute: %s\n",argv[1]);
      perror("Reason");
      kill(getppid(),SIGKILL);   /* kill waiting parent */
      exit(errno);               /* execvp failed, no child - exit immediately */
    }
  else if(pid != -1)
    {
      sleep(TIMEOUT);
      if(kill(0,0) == 0)         /* are there processes left? */
    {
      fprintf(stderr,"\nRunSafe: Attempting to kill remaining (child) processes\n");
      kill(0, SIGKILL);      /* send SIGKILL to all child processes */
    }
    }
  else
    {
      fprintf(stderr,"RunSafe failed to fork off child process\n");
      perror("Reason");
        }

}

What does my warning mean when I compile it?

$ gcc -o RunSafe RunSafe.c -lm 
RunSafe.c: In function ‘main’:
RunSafe.c:30:44: warning: incompatible implicit declaration of built-in function ‘strlen’ [enabled by default]

Why can’t I execute the file?

$ file RunSafe
RunSafe: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.24, BuildID[sha1]=0x0a128c8d71e16bfde4dbc316bdc329e4860a195f, not stripped
ubuntu@ubuntu:/media/Lexar$ sudo chmod 777 RunSafe
ubuntu@ubuntu:/media/Lexar$ ./RunSafe
bash: ./RunSafe: Permission denied
ubuntu@ubuntu:/media/Lexar$ sudo ./RunSafe
sudo: ./RunSafe: command not found

Answer 1

First, you need to #include <string.h> to get rid of that warning.

Second, the OS is probably preventing you from executing programs on the /media/Lexar filesystem, no matter what their permission bits are. If you type mount you’ll probably see the noexec option for /media/Lexar.