Это решение твоего шестого варианта. Предыдущий файл был для пятого.

exe.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <dirent.h>
#include <semaphore.h>
#include <sys/stat.h>
#include <unistd.h>

sem_t * out_sem;

int getsize(char *name)
{
  struct stat buf;
  stat(name,&buf);
  return buf.st_size;
}

int isexecutable(char *name)
{
  return !access(name,X_OK);
}

int inbounds(int min,int max,char *name)
{
  return ((getsize(name) > min) && (getsize(name) < max));
}

void processdir(int min,int max,char *name,FILE *outfile)
{
  pid_t pid;
  DIR *dir;
  DIR *dir_desc;
  struct dirent *cur_entry;
  char path[1024];
  char *filename;
  int total;
  pid = getpid();
  total = 0;
  dir=opendir(name);
  chdir(name);
  strcpy(path, getwd(NULL));
  while(cur_entry = readdir(dir)){
    if(strcmp(cur_entry->d_name, "..") && strcmp(cur_entry->d_name,".")){
      if(dir_desc = opendir(cur_entry->d_name)){ // this is a directory
	closedir(dir_desc);
	processdir(min,max,cur_entry->d_name,outfile);
	chdir(path);
      }else if(isexecutable(cur_entry->d_name) // this is an executable file
	       && inbounds(min,max,cur_entry->d_name)){ // with desired size
	sem_wait(out_sem);
	printf("PID: %d | PATH: %s | FILE: %s | SIZE: %d | TOTAL: %d\n",
		pid, path, cur_entry->d_name, getsize(cur_entry->d_name), total);
	fprintf(outfile,"PATH: %s | FILE: %s | SIZE: %d\n",
		path, cur_entry->d_name, getsize(cur_entry->d_name));
	sem_post(out_sem);
	total++;
      }
    }
  }
}

int main(int argc, char *argv[])
{
  struct dirent * cur_entry;
  int min,max;
  DIR *dir_desc;
  DIR *dir;
  FILE *outfile;
  char *path;
  int total;
  int procnum;
  int N;
  pid_t p;
  
  // check
  if(argc != 5){
    printf("usage: ./exe <min> <max> <dir> <outfile>");
    exit(1);
  }
  
  // initialization
  min = atoi(argv[1]);
  max = atoi(argv[2]);
  out_sem = sem_open("max_sem", O_CREAT);
  sem_post(out_sem);
  procnum = 0;
    dir = opendir(argv[3]);
  outfile = fopen(argv[4],"w");
  if(!dir){
    printf("\"%s\" is not a directory\n",argv[1]);
    exit(2);
  }
  if(!outfile){
    printf("Can't open file \"%s\" for writing. Exiting.\n",argv[1]);
    exit(3);
  }
  chdir(argv[3]);
  path=getwd(NULL);
  printf("N = ");
  scanf("%d",&N);
  N--; // 4 process maximum means 3 child + 1 parent. Now N will be max child.

  // main program loop
  while(cur_entry = readdir(dir)){
    if(strcmp(cur_entry->d_name,"..") && strcmp(cur_entry->d_name,".")){
      if(dir_desc = opendir(cur_entry->d_name)){ // this is a directory
	sem_wait(out_sem);
	// printf("DIR: %s\n", cur_entry->d_name);
	sem_post(out_sem);
	closedir(dir_desc);
	if(procnum<N){
	  procnum++;
	}else{
	  wait3(0,0,0); // wait any child process to exit
	}
	p = fork();
	if(!p){
	  processdir(min,max,cur_entry->d_name,outfile);
	  fclose(outfile);
	  exit(0);
	}else{
	  sem_wait(out_sem);
	  // printf("started %d for %s\n",p,cur_entry->d_name);
	  sem_post(out_sem);
	}
      }else if(isexecutable(cur_entry->d_name) // this is an executable file
	       && inbounds(min,max,cur_entry->d_name)){ // with desired size
      	sem_wait(out_sem);
	fprintf(outfile,"PATH: %s | FILE: %s | SIZE: %d\n",
	       path, cur_entry->d_name, getsize(cur_entry->d_name));
	sem_post(out_sem);
	total++;
      }
    }
  }
  while(procnum--){
    wait3(0,0,0);
  }
  printf("Total files without subdirectories: %d\n",total);
  fclose(outfile);
  return 0;
}