порождать процесс (spawn a process)
Возвращаемое значение (Return value)
Upon successful completion, posix_spawn() and posix_spawnp()
place the PID of the child process in pid, and return 0. If
there is an error during the fork() step, then no child is
created, the contents of *pid are unspecified, and these
functions return an error number as described below.
Even when these functions return a success status, the child
process may still fail for a plethora of reasons related to its
pre-exec() initialization. In addition, the exec(3) may fail.
In all of these cases, the child process will exit with the exit
value of 127.
