The most popular open-source compilers and development tools on Linux are the GNU family (gcc, gmake, etc.). These same tools are also available on HP-UX, so many sites install them and begin preparing their applications prior to any actual move to Linux. What you will find is that while GCC and Linux are reasonably solid in terms of support for the relevant ANSI and POSIX standards, items such as compile options and make files will probably need updating. Of course, if your applications rely on low-level HP-UX interfaces, contain assembler language or kernel code, or are otherwise non-portable, then your porting effort can grow substantially.
One area many people overlook in ports like this is the need to become familiar with some new debugging skills. In addition to basic source-level debugging capabilities provided by the GNU debugger (gdb), Linux also has a wide range of additional tools that can be a big help when diagnosing errors. Although HP-UX has similar capabilities in many areas, your port will be smoother if you take the time to learn some of the Linux equivalents.
Finally, you will also want to verify exactly what add-ons your HP-UX applications require so that you can ensure that the same functions are available on Linux. For instance, you may be using a database or cryptography library of some sort that may not be available at all on Linux. Generally, you will be able to find open-source equivalents, but you may find that the open-source equivalents require sometimes significant changes to your application before you can use them.
This was first published in March 2003