diff --git a/src/userprog/process.c b/src/userprog/process.c
index 6c82064..6af78e2 100644
--- a/src/userprog/process.c
+++ b/src/userprog/process.c
@@ -19,11 +19,13 @@
 #include "threads/vaddr.h"
 #include "threads/malloc.h"
 
+#define FD_MIN 2            /* Min value for file descriptors. */
+
 /* Structure for arguments. */
 struct arguments
   { 
-    int argc;                /* Number of arguments. */ 
-    char **argv;             /* Array of arguments. */
+    int argc;               /* Number of arguments. */
+    char **argv;            /* Array of arguments. */
   };
 
 static thread_func start_process NO_RETURN;
@@ -105,6 +107,7 @@ start_process (void *arguments)
   else
     curr->status |= PROCESS_FAIL;
   curr->exec_file = exec_file;
+  curr->fd_next = FD_MIN;
   list_init (&curr->file_list);
 
   /* If load failed, quit. */ 
@@ -166,6 +169,13 @@ process_exit (void)
   proc->status |= PROCESS_EXIT;
   list_remove (&proc->elem);
   file_close (proc->exec_file);
+  for (e = list_begin (&proc->file_list); e != list_end (&proc->file_list);)
+    {
+      struct process_file *pfe = list_entry (e, struct process_file, elem);
+      e = list_next (e);
+      file_close (pfe->file);
+      free (pfe);
+    }
 
   struct thread *curr = thread_current ();
   uint32_t *pd;
@@ -225,6 +235,41 @@ process_find_child (struct process *proc, pid_t pid)
     }
   return NULL;
 }
+
+/* Returns a process' file by the file descriptor. */
+struct file *
+process_get_file (int fd)
+{
+  struct list *list = &process_current ()->file_list;
+  struct list_elem *e;
+  for (e = list_begin (list); e != list_end (list); e = list_next (e))
+    {
+      struct process_file *pfe = list_entry (e, struct process_file, elem);
+      if (pfe->fd == fd)
+        return pfe->file;
+    }
+  return NULL;
+}
+
+/* Sets the file into the current process and returns the file descriptor. */
+int
+process_set_file (struct file *file)
+{
+  /* Create a file element. */
+  struct process_file *pfe;
+  pfe = (struct process_file *) malloc (sizeof (struct process_file));
+  if (pfe == NULL)
+    return -1;
+
+  /* Initialize the file element. */
+  struct process *curr = process_current ();
+  pfe->fd = curr->fd_next++;
+  pfe->file = file;
+  list_push_back (&curr->file_list, &pfe->elem);
+
+  /* Return the file descriptor. */
+  return pfe->fd;
+}
 
 /* We load ELF binaries.  The following definitions are taken
    from the ELF specification, [ELF1], more-or-less verbatim.  */
diff --git a/src/userprog/process.h b/src/userprog/process.h
index 0cf4b28..56b17d8 100644
--- a/src/userprog/process.h
+++ b/src/userprog/process.h
@@ -26,6 +26,7 @@ struct process
     int status;                     /* Process status. */
     int exit_code;                  /* Exit code. */
     bool is_waiting;                /* Whether parent is waiting or not. */
+    int fd_next;                    /* File descriptor tracker. */
   };
 
 /* A file held by some process. */
@@ -42,5 +43,7 @@ void process_exit (void);
 void process_activate (void);
 struct process *process_current (void);
 struct process *process_find_child (struct process *proc, pid_t pid);
+struct file *process_get_file (int fd);
+int process_set_file (struct file * file);
 
 #endif /* userprog/process.h */
diff --git a/src/userprog/syscall.c b/src/userprog/syscall.c
index 57334c1..b89d593 100644
--- a/src/userprog/syscall.c
+++ b/src/userprog/syscall.c
@@ -249,10 +249,29 @@ syscall_remove (const char *file)
   return success;
 }
 
+/* Opens the file. Returns a nonnegative integer handle,
+   a file descriptor, or -1 if the file could not be opened. */
 static int 
 syscall_open (const char *file)
 {
-  return 0;
+  /* Check the validity. */
+  validate_ptr (file);
+
+  /* Open the file. */
+  lock_acquire (&filesys_lock);
+  struct file *f = filesys_open (file);
+  if (f == NULL)
+    {
+      lock_release (&filesys_lock);
+      return -1;
+    }
+
+  /* Set the file. */
+  int fd = process_set_file (f);
+
+  /* Return the file descriptor. */
+  lock_release (&filesys_lock);
+  return fd;
 }
 
 static int