GDB or GNU Debugger is the most popular debugger for UNIX platforms. This is a program that runs on other programs and allows the users to exercise the control over these programs and to examine variables when problems arise. GDB lets you to see what is going on inside another program while it executes or what the other program was doing at the time it crashed.

GDB can do four main kinds of things to help you catch bugs in the act. It allows you start your program and specify if anything affects the behavior of the program. It makes the program stop on specified conditions and examines what has happened when your program has stopped and change things in it. Therefore, you can experiment with correcting the effects of one bug along with learn about the other.

GDB is used to debug programs written in C and C++. You can also use it to debug programs written in Fortran, Pascal, Modula 2 and Objective C. GDB is open source and free software, available and used under the terms of GNU General Public License. Richard Stallman was the original author of GDB.