6.7. Debugging an already-running process
- attach process-id
This command attaches to a running process--one that was started
outside gdb. (info files shows your active
targets.) The command takes as argument a process ID. The usual way to
find out the process-id of a Unix process is with the ps utility,
or with the jobs -l shell command.
attach does not repeat if you press [RET] a second time after
executing the command.
To use attach, your program must be running in an environment
which supports processes; for example, attach does not work for
programs on bare-board targets that lack an operating system. You must
also have permission to send the process a signal.
When you use attach, the debugger finds the program running in
the process first by looking in the current working directory, then (if
the program is not found) by using the source file search path
(refer to Section 9.4 Specifying source directories). You can also use
the file command to load the program.
Refer to Section 17.1 Commands to specify files.
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 would rather the
process continue running, you may use the continue command after
attaching gdb to the process.
- detach
When you have 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
are ready to attach another process or start one with run.
detach does not repeat if you press [RET] 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 (refer to Section 21.7 Optional warnings and messages).
