GDB
GDB stands for GNU Debugger. It is a program for *nix related systems that allows you to view stacktrace and coredumps of your servers if it crashes.
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Getting GDB
Typically GDB comes installed on most *nix distro's. It comes installed on FreeBSD 7.1-RELEASE or newer if the ports collection is installed. Typically, it will be located in /usr/bin/gdb, but if it is not, you can either compile it from source or install it using your package manager for your distribution.
Debian Based (apt-get, aptitude or synaptic)
On Debian based systems, you can use apt-get or aptitude, or the synaptic package manager to install gdb. If you prefer the terminal, you can issue ONE of the following to install gdb:
[sudo] aptitude install gdb [sudo] apt-get install gdb
If you have access to gdm and the synaptic package manager, you can simply search for 'gdb' and mark for complete installation.
YUM based (Redhat/CentOS)
On YUM based systems, you can simply issue the following to install gdb via RPM packages:
yum install gdb
*BSD based
Typically GDM will come with an install of FreeBSD, but if it's not, it is best to make it from source, skip ahead.
Compiling from source
Use your favourite download manager (wget, etc) to get the .tar.gz of the latest stable version of gdb from gdb's website. (http://www.gnu.org/software/gdb/)
Extract the .tar.gz using the following command:
tar -zxf gdb-x.xx.tar.gz
You need a GCC compatible compiler, so if you don't have one, get one now. there is a 99% chance that your distribution comes with a gcc compiler.
./configure && make && make install
Should install it for use. If you're on a *BSD based system, you may have to issue the following command to be able to use it.
% rehash
Using gdb with Hercules
Go to Your Hercules Folder and type the following command
ulimit -u unlimited
Restart the server then, Find out which program(map/char/login server) crashed and its core file (should be named the same as the server file with an additional ".core" extension).. then on the console, type:
gdb xxx-server xxx-server.core
[xxx = map/char/login (The one which is crashing)]
You should get some limited output of the problem, or if the servers do not have a trace, you will get the following error:
No stack.
If it says Dump file was not found, then type the following command(The file is saved with other name)
gdb xxx-server core
[xxx = map/char/login (The one which is crashing)]
If a valid dump was found, you should get a prompt
gdb>
At that prompt, type:
gdb> bt full
And that will give you a full output of the problem area and a line number in which you should look for the crash. This just told you where the crash is located and what line you should look at to fix it. If you feel that is an Hercules development problem, feel free to submit a bug with that full report and one of the core developers can look into it.
Note: in order to obtain detailed information from gdb, Hercules needs to be compiled with special flags. Normal builds are optimized for performance and don't include debug information. To build in debug mode, it is necessary to pass --enable-debug=gdb and --disable-lto to the configure script as follows:
./configure --enable-debug=gdb --disable-lto make clean make sql
Example
> gdb ./map-server (gdb) r <<< wait until it crash >>> (gdb) bt full
