On most systems, GDB has no special support for debugging
programs which create additional processes using the
function. When a program forks, GDB will continue to debug the
parent process and the child process will run unimpeded. If you have
set a breakpoint in any code which the child then executes, the child
will get a
SIGTRAP signal which (unless it catches the signal)
will cause it to terminate.
However, if you want to debug the child process there is a workaround
which isn't too painful. Put a call to
sleep in the code which
the child process executes after the fork. It may be useful to sleep
only if a certain environment variable is set, or a certain file exists,
so that the delay need not occur when you don't want to run GDB
on the child. While the child is sleeping, use the
ps program to
get its process ID. Then tell GDB (a new invocation of
GDB if you are also debugging the parent process) to attach to
the child process (see section Debugging an already-running process). From that point on you can debug
the child process just like any other process which you attached to.
On HP-UX (11.x and later only?), GDB provides support for
debugging programs that create additional processes using the
By default, when a program forks, GDB will continue to debug the parent process and the child process will run unimpeded.
If you want to follow the child process instead of the parent process,
use the command
set follow-fork-mode mode
vfork. A call to
vforkcreates a new process. The mode can be:
If you ask to debug a child process and a
vfork is followed by an
exec, GDB executes the new target up to the first
breakpoint in the new target. If you have a breakpoint set on
main in your original program, the breakpoint will also be set on
the child process's
When a child process is spawned by
vfork, you cannot debug the
child or parent until an
exec call completes.
If you issue a
run command to GDB after an
call executes, the new target restarts. To restart the parent process,
file command with the parent executable name as its
You can use the
catch command to make GDB stop whenever
exec call is made. See section Setting catchpoints.
Go to the first, previous, next, last section, table of contents.