Close-on-exec

So, close each unnecessary file descriptor before exec

Quite a pain
You may accidentally miss some
You may accidentally close something important

Better yet, set the close-on-exec flag after opening the file

   fd = open( FILENAME, FLAGS [,mode] );
   fcntl( fd, F_SETFD, 1 );

Now, these files will automatically be closed with no work or coding on your part.