PTRACE(2)

NAME
ptrace - process trace

SYNOPSIS
#include <sys/ptrace.h>

int ptrace(int request, int pid, int addr, int data);

DESCRIPTION
Ptrace 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. A traced process runs until a signal occurs. Then it stops and the parent will be notified with wait(2). When the process is in the stopped state, its memory can be read and written. The parent can also cause the child to continue execution, with optional ignoring the signal which caused stopping.

The value of the request argument determines the precise action of the system call:

PTRACE_TRACEME
    This process is to be traced by its parent. The parent should be expecting to trace the child.

PTRACE_PEEKTEXT, PTRACE_PEEKDATA
    Read word at location addr.

PTRACE_PEEKUSR
    Read word at location addr in the USER area.

PTRACE_POKETEXT, PTRACE_POKEDATA
    Write word at location addr.

PTRACE_POKEUSR
    Write word at location addr in the USER area.

PTRACE_SYSCALL, PTRACE_CONT
    Restart after signal.

PTRACE_KILL
    Send the child a SIGKILL to make it exit.

PTRACE_SINGLESTEP
    Set the trap flag for single stepping.

PTRACE_ATTACH
    Attach to the process specified in pid.

PTRACE_DETACH
    Detach a process that was previously attached.

NOTES
init, the process with process ID 1, may not use this function.

RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is set appropriately.

ERRORS

EPERM
    The specified process (i.e., init), cannot be traced, or is already being traced.

ESRCH
    The specified process does not exist.

EIO Request is not valid.

CONFORMING TO
SVr4, SVID EXT, AT&T, X/OPEN, BSD 4.3

SEE ALSO
gdb(1), exec(3), signal(2), wait(2)