A common solution to #2 is to open a pipe prior to the fork(), then write to it in the child following the exec. In the parent, a successful read means the exec failed; an unsuccessful read means the exec succeeded and the write never took place.
// ignoring all errors except from execvp...
int execpipe[2];
pipe(execpipe);
fcntl(execpipe[1], F_SETFD, fcntl(execpipe[1], F_GETFD) | FD_CLOEXEC);
if(fork() == 0)
{
close(execpipe[0]);
execvp(...); // on success, never returns
write(execpipe[1], &errno, sizeof(errno));
// doesn't matter what you exit with
_exit(0);
}
else
{
close(execpipe[1]);
int childErrno;
if(read(execpipe[0], &childErrno, sizeof(childErrno)) == sizeof(childErrno))
{
// exec failed, now we have the child's errno value
// e.g. ENOENT
}
}
This lets the parent unambiguously know whether the exec was successful, and as a byproduct what the errno value was if unsuccessful.
If the exec was successful, the child process may still fail with an exit code, and examining the status with the WEXITSTATUS
macro give you that condition as well.
NOTE: Calling waitpid
with the WNOHANG
flag is nonblocking, and you may need to poll the process until a valid pid is returned.