How to detect where my app collapsed in linux

Question

HI, i am recently in a project in linux written in C. This app has several processes and they share a block of shared memory...When the app run for about several hrs, a process collapsed without any footprints so it's very diffficult to know what the problem was or where i can start to review the codes.... well, it could be memory overflown or pointer malused...but i dunno exactly... Do you have any tools or any methods to detect the problems... It will very appreciated if it get resolved. thanx for your advice...

Answer 1

Valgrind is where you need to go next. Chances are that you have a memory misuse problem which is benign -- until it isn't. Run the programs under valgrind and see what it says.

Answer 2

Before you start the program, enable core dumps:

ulimit -c unlimited

(and make sure the working directory of the process is writeable by the process)

After the process crashes, it should leave behind a core file, which you can then examine with gdb:

gdb /some/bin/executable core

Alternatively, you can run the process under gdb when you start it - gdb will wake up when the process crashes.

Answer 3

You could also run gdb in gdb-many-windows if you are running emacs. which give you better debugging options that lets you examine things like the stack, etc. This is much like Visual Studio IDE.

Here is a useful link

http://emacs-fu.blogspot.com/2009/02/fancy-debugging-with-gdb.html

Answer 4

I agree with bmargulies -- Valgrind is absolutely the best tool out there to automatically detect incorrect memory usage. Almost all Linux distributions should have it, so just emerge valgrind or apt-get install valgrind or whatever your distro uses.

However, Valgrind is hardly the least cryptic thing in existence, and it usually only helps you tell where the program eventually ended up accessing memory incorrectly -- if you stored an incorrect array index in a variable and then accessed it later, then you will still have to figure that out. Especially when paired with a powerful debugger like GDB, however (the backtrace or bt command is your friend), Valgrind is an incredibly useful tool.

Just remember to compile with the -g flag (if you are using GCC, at least), or Valgrind and GDB will not be able to tell you where in the source the memory abuse occurred.