Unix Core Files

When you are running a program on a UNIX machine that terminates abnormally, possibly because it crashed, the operating system creates a core file in the current working directory. The system dumps information into the core file about what the program was doing at the time it crashed, e.g., which subroutine it was calling or what memory address it was accessing. The format of the information in this file is pretty cryptic, but the file can be post-processed by an appropriate debugging tool to give application developers useful information. If you are not trying to diagnose a bug in an application, the file contains no other useful information and can be safely deleted. In fact, it should be deleted because often it is quite large (>100 MB).

How can you prevent the core file from getting so large? One option is to create a directory named core in your current working directory. When the application crashes, the operating system cannot write the core file because a directory with the name already exists. A second option is to set a limit on how big the core file is allowed to grow using the command

limit coredumpize xxxx

xxxx is the maximum size in kB that the core file is allowed to be. In theory, the core file will never exceed the limit. However, in practice, some operating systems ignore it. This command has been incorporated into the standard NML .cshrc file.