Linux file size limits

On Mon, 1 Oct 2001, Borislav Kovacevic wrote:
 >
 > Hi CCLers,
 > My question is: why are total size of temporary files in Gussian (rwf) and
 > in Molpro limited to max. 16 Gb under the Linux operating sistem.
 > I know that in 32 bit operating system maximum file size is 2GB.
 > In Gaussian I can split rwf files but 8 (16GB) is maximum number of
 > them. Why?
 > In new version of Linux (kernel 2.4) this 2 Gb problem is solved, i.e. I
 > can have a file larger than 2 Gb. I tried with Molpro and sucessfully
 > wrote file larger than 2 Gb, but it seems that there is a 16 Gb limit
 > anyway.
 > Why this limit exists and is there any way to change it?
 >
 >              Thanks very much!
 >
 I cannot help with the MolPro limits as I'm not familiar enough with the
 details of that code.  However, I can try to clarify a few points regarding
 filesize limits under Linux on 32-bit systems (e.g, ix86, athlon, etc.).
 This doesn't directly address your question, but does deal with this
 general topic and other questions recently posted to this list.
 (1) The 2.4.X Linux kernels support filesizes > 2 GB, including under the
 ext2 filesystem.
 (2) For C-language programs, even with a 2.4.X kernel, one must use the
 correct -D flags to make use of large-file support.  These are:
 -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE
 They must be added for any codes which call low-level I/O routines such
 as open(), read(), write(), close(), etc.  This will work for both GNU
 and Portland compilers, by the way.
 (3) For Fortran programs, if one is using the Portland Group compilers,
 PGI has provided large-file support through their I/O library:
 http://www.pgroup.com/faq.htm#execute1k
 If, instead, one if using the GNU Fortran compiler g77, it is still
 possible to obtain code capable of reading/writing large files, but a bit
 more problematic.  If anyone cares to do this, let me know and I'll explain
 how.  If there's sufficient interest on this list, I'll post it.
 -Daniel
 --
 T. Daniel Crawford                           Department of Chemistry
 crawdad-0at0-vt.edu                                    Virginia Tech
 www.chem.vt.edu/chem-dept/crawford
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