### 19.1 Active Targets

There are multiple classes of targets such as: processes, executable files or recording sessions. Core files belong to the process class, making core file and process mutually exclusive. Otherwise, GDB can work concurrently on multiple active targets, one in each class. This allows you to (for example) start a process and inspect its activity, while still having access to the executable file after the process finishes. Or if you start process recording (see Reverse Execution) and `reverse-step` there, you are presented a virtual layer of the recording target, while the process target remains stopped at the chronologically last point of the process execution.

Use the `core-file` and `exec-file` commands to select a new core file or executable target (see Commands to Specify Files). To specify as a target a process that is already running, use the `attach` command (see Debugging an Already-running Process).