The READONLY keyword specifies that an existing file can be read or found, but it cannot be written to. It takes the following form:
READONLY
The Fortran I/O system's default file access privileges are read-write. If access is denied, the I/O system automatically retries accessing the file for read access.
However, if you specify compiler option VMS, the I/O system does not retry accessing for read access. This can cause run-time I/O errors if the file protection does not permit write access. In this case, if you wish to read a file for which you do not have write access, you must specify READONLY.