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Writing and Running Programs on a UNIX/Linux Computer

• What Types of Programming are Supported?
• How Do I Use Compilers on Linux Systems?
• How Do I Use Debuggers on Linux Systems?
• How Do I Use the Compilers on 64-bit Linux Computers?

What Types of Programming are Supported

• Basic and advanced programming in Fortran, C/C++, Java
• Basic GPU programming under CUDA, CUDA directives under Fortran and C (PGI compilers), Basic MATLAB CUDA programming
• Web programming: PHP, HTML, CSS, Database programming and support
• Scripting: Perl, Pyhton, CSH, BASH, KSH
• Parallel Programming: Converting serial codes to parallel using MPI, OpenMP, Hybrid programming
• Code Debugging: use Totalview to debug  codes
• Code development: Serial and parallel codes
• Code proting: Mainly to Linux environments including Math and Scientific libraries
• Application programming: Matlab programming, SAS programming, Visualization with Visit and VTK

How Do I Use Compilers on Linux Systems?

Most Research Computing Linux computers have three different kinds of compilers: GNU compilers, Portland Group compilers, and Intel compilers.

Below is a table that shows the different compilers and their commands:

No one compiler works best for all kinds of code. If you are interested in optimizing your application, you will want to test various compiler options and compilers to see which ones work the best for your application. There is a man page for each compiler that lists the compiler options.

In general, gcc/g++ is the most flexible since it runs on a variety of different computer platforms. Many people use gcc/g++ so it will be easy to port their code to other platforms. g77 and gfortran are the Fortran77 GNU compilers and is not as robust as the Portland Group and Intel Fortran compilers.

The Portland Group compilers will compile f77, f90, C, and C++ codes. Many Fortran codes use extensions to the language, and the Portland Group compilers support those extensions. Portland Group recommends you use the pgf90 for both Fortran 90 and Fortran 77 codes to gain additional code speed up.

The Intel compilers do a good job of compiling code to make use of the architectural features of the Intel processors.

Here is a table of frequently used compiler flags, common to the above compilers.

Compiler Option	What the option does
-c	Produce an object file only
-o filename	Create an executable called filename(the default is a.out)
-O {0,1,2,3}	Specify the optimization level ( 0 is none and 3 is most aggressive)
-g	Include a symbol table, needed for debugging
-pg	Generate profiling code
-I	Look for include files in this directory (default include directory is: /usr/include)
-L	Look for libraries in this directory (default library directory: /lib, /usr/lib, /usr/lib64
-larchive	Link in a library called libarchive.so (or .a)
-static	Link only with static libraries (compilers use shared libraries by default)

For more options and detailed information:

• Consult man pages (e.g., man gcc) for more options and more detailed information. Send questions, corrections, or additional information about these compilers to Research Computing

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How Do I Use Debuggers on Linux Systems?

In general, you should use either the debugger that is supplied with each type of compiler or a general-purpose debugger like totalview. The table below provides the compilers and their associated debuggers for the compilers installed on the Research Computing Linux Computers.

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How Do I Use the Compilers on 64-bit Linux Computers

A 64-bit computer can handle more computations, memory, and I/O than a 32-bit computer. To take advantage of this additional power, software must be built with 64-bit compilers. The 64-bit computer can run 32-bit applications, but running them in 32-bit mode doesn't use all the expanded capabilities of the 64-bit computer. However, software built to use a 64-bit computer cannot run on a 32-bit computer.

All of the C/C++ and FORTRAN compilers on the public 64-bit Linux computers  will build 64-bit applications by default when you run them on a 64-bit computer. You can specify options to these compilers to build a 32-bit executable instead of a 64-bit. The table below provides more information on these options for the installed  compilers.

If you plan to build your application on both 32-bit and 64-bit Linux computers, and you want to use the same executable on both, compile the program for a 32-bit computer. If you plan to run only on  a 64-bit computer, compile the program for 64-bit, as it will run more efficiently.

The File command tells you which kind of application your executable is. For example, the following information is about an executable called shapley.

file shapley

shapley: ELF 64-bit LSB executable, AMD x86-64, version 1 (SYSV).
for GNU/Linux 2.4.0, dynamically linked (uses shared libs), not stripped

If you try to run a 64-bit executable on a 32-bit computer, you will get an error message that says, "Exec format error. Wrong Architecture.".

Compiler Commands for Building 32-bit and 64-bit Applications on 64-bit Linux Computers

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