Tips for hackers that live in the moment

How to handle .core files

When I develop or debug C++ program, I often have to deal with .core files that arise from crashes.

While everyone knows about:

ulimit -c unlimited

That enables the generation of such core files, it it also very useful to know about the /proc/sys/kernel/core_pattern file that controls where and how the .core files will be generated.

Here is the content of mine:

/core/core-%e-pid-%p-sig-%s-time-%t

One can configure it for the current session doing, as root:

echo "/core/core-%e-pid-%p-sig-%s-time-%t" >> /proc/sys/kernel/core_pattern

It can also be configured permanently by adding the following line in /etc/sysctl.conf:

kernel.core_pattern=/core/core-%e-pid-%p-sig-%s-time-%t

For the sake of completeness, here is the list of all the available special sequences:

%p: pid
%: '%' is dropped
%%: output one '%'
%u: uid
%g: gid
%s: signal number
%t: UNIX time of dump
%h: hostname
%e: executable filename
%: both are dropped

Happy debugging !

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