Hello, for posix_start I would suggest following in order to pass the error of ::execve to the parrent: int fd[2]; if ( ::pipe( fd) < 0) // create a pipe throw sys::system_error( errno, sys::errno_ec); if ( ( pid = ::fork() ) < 0) // fork new process throw sys::system_error( errno, sys::errno_ec); if ( pid == 0) // child { ::close( fd[0]); // close one end of the pipe ::fcntl( fd[1], F_SETFD, FD_CLOEXEC); // close other end of pipe if this process is replaced by ::execve struct sigaction act; // clear all signal handlers ::sigemptyset( & act.sa_mask); act.sa_handler = SIG_DFL; act.sa_flags = 0; for ( int sig = 1; sig < NSIG; sig++) ::sigaction( sig, & act, 0); ... ::execve( cl.get_executable().c_str(), args.second, envp); // replace by new application int msg = errno; // reached only if ::execve failed ::write( fd[1], & msg, sizeof msg); // write error number to pipe ::_exit( errno); // exit } // parent ::close( fd[1]); // close one end of pipe while( true) { int msg; // error number passed from child process int n = ::read( fd[0], & msg, sizeof msg); if ( n == sizeof( int) ) { // child has written something to pipe ::close( fd[0]); throw sys::system_error( msg, sys::errno_ec) ); } else if (n == -1) { if ( errno == EINTR) continue; } // interrupted break; // EOF of pipe } ::close( fd[0]); return child( pid); regards, Oliver