READONLY

  Prohibits WRITE access to the file.  Enables users with READ access
  to access the file.

  READONLY is similar to specifying ACTION='READ', but READONLY
  prevents deletion of the file if it is closed with STATUS='DELETE'
  in effect.

  Default file access privileges are READWRITE, which can cause
  run-time I/O errors if the file protection does not permit write
  access.

  The READONLY specifier has no effect on the protection specified
  for a file.  Its main purpose is to allow a file to be read
  simultaneously by two or more programs.  For example, use READONLY
  if you wish to open a file so you can read it, but you also want
  others to be able to read the same file while you have it open.