+.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\" @(#)2.5.t 8.6 (Berkeley) 5/29/94
+.\"
+.Sh 2 "Process debugging
+.Sh 3 "Traditional debugging
+.LP
+Debuggers traditionally use the
+.Fn ptrace
+interface:
+.DS
+.Fd ptrace 4 "process trace
+ptrace(request, pid, addr, data);
+int request, pid, *addr, data;
+.DE
+This interface provides a means by which a parent process may
+control the execution of a child process,
+and examine and change its core image.
+Its primary use is for the implementation of breakpoint debugging.
+There are four arguments whose interpretation
+depends on a request argument.
+A process being traced behaves normally until it
+encounters a signal (whether internally generated like
+``illegal instruction'' or externally generated
+like ``interrupt'').
+Then the traced process enters a stopped state
+and its parent is notified via
+.Fn wait .
+When the child is in the stopped state,
+its core image can be examined and modified using
+.Fn ptrace .
+Another ptrace request can then cause the child either to terminate
+or to continue, possibly ignoring the signal.