I have a command line application that when run does not do what it is supposed to do and at a certain point leaves the message:
What does this mean? What should I do?
A segmentation fault is the result of a memory access violation. The program has referred to a memory address outside of what was allocated to it, and the OS kernel responds by killing the program with SIGSEGV.
This is a mistake, since there is no point in trying to access inaccessible memory (it cannot be done). Mistakes of this sort are easy to make, however, particularly in languages such as C and C++ (which account for a lot of common applications). It indicates a bug in either the program itself or a library it links to. If you wish to report the bug (do -- this helps), it is a good idea to include a backtrace of the events that led up to the seg fault.
To do this, you can run the program inside
A paragraph about copyright and licensing will appear, and at the end a prompt with the cursor:
The second line of output here is just an example. Now type
If it is longer, you'll only get a screenful at a time and there will be a
Someone will hopefully get back to you in not too long. Filing bugs is a usually appreciated.
This means that application has a bug.
Core files will also be very useful for the developers other than yourself - they contain full state of the program at the moment of the crash; if you are going to file a bug report, attach them, and in some cases your app binary. Be aware that there is small chance that your personal data like account numbers, passwords and similar could remain in memory of the program at the moment of the crash. In many cases, reporting just backtrace of crashed thread is big help for developers to find the problem. To get backtrace, you could load core file with debugger (like