Debugging an already-running process

To use attach, you must have permission to send the process a signal.

attach process-id
This command attaches to a running process—one that was started outside GDB. (The info files command shows your active targets.) The command takes as its argument a process ID. To find out a process ID, use the pidin utility (see the Utilities Reference), or use GDB's info pidlist command.

The attach command doesn't repeat if you press Enter a second time after executing the command.

When using attach, you should first use the file command to specify the program running in the process and load its symbol table.

The first thing GDB does after arranging to debug the specified process is to stop it. You can examine and modify an attached process with all the GDB commands that are ordinarily available when you start processes with run. You can insert breakpoints; you can step and continue; you can modify storage. If you want the process to continue running, use the continue command after attaching GDB to the process.

When you've finished debugging the attached process, you can use the detach command to release it from GDB control. Detaching the process continues its execution. After the detach command, that process and GDB become completely independent once more, and you're ready to attach another process or start one with run. The detach command doesn't repeat if you press Enter again after executing the command.

If you exit GDB or use the run command while you have an attached process, you kill that process. By default, GDB asks for confirmation if you try to do either of these things; you can control whether or not you need to confirm by using the set confirm command.