通过系统调用启动bash脚本的Linux C ++程序始终返回-1

Question

I have a chain of programs as follows:

C++ program "A" launches another C++ program "B" which launches a bash script.

To launch the bash script, I am using:

int returnVal = system("pathToScript/myScript.sh");

I can see the output of the script in my log file, so it's definitely being executed.

Problem is, returnVal is always -1 no matter what the script returns. I even hard coded an "exit 3" in the script and I'm still getting a returnVal of -1 when I launch it via the system call.

Running the script standalone in a terminal and echoing "$?" shows a return value of 3 as expected.

So why is the exit code breaking when I run it through a chain of C++ programs? Is there any way to get around this?

EDIT - Using perror shows a "No child processes" error message.

EDIT - As an alternative, I'm trying to use fork/exec/wait to execute my script, but I'm getting random exit codes such as 182, 56, 163, 62, 51, etc... Code below:

pid_t pid = vfork();

switch (pid)
{
  case -1:
     cout << "Failed to fork." << endl;

  case 0: // Child process
     cout << "Child process launched!" << endl;
     execl("/pathToScript/myScript.sh", "/pathToScript/myScript.sh", "someArgument", NULL);
     cout << "execl call failed." << endl;
     exit(0);

  default:
     int status;

     cout << "Waiting for process to complete..." << endl;

     waitpid(pid, &status, 0); // Wait for the process to complete.

     cout << "Process exited with status: " << WEXITSTATUS(status) << endl;
}

Why am I getting random exit status here?

Appreciate any advice. Thanks!

Answer 1

As mentioned in comments your problem is ignorig SIGCHLD . Ignoring SIGCHLD can be used to prevent the creation of zombies. So by setting it disposition to default you can break something.

Here example:

signal (SIGCHLD, SIG_DFL);
system ("some_program");
signal (SIGCHLD, SIG_IGN);

If some child process (not child in system ) terminated between execution first and third line, it will become a zombie.

If you want solve this resources leak correctly, you should use another method (double fork or wait ) for solving zombies problem.

---

Why am I getting random exit status here?

Because waitpid call failed. If you print out return value of waitpid it will be -1 . The value of errno most likely will be ECHILD . Setting disposition of SIGCHLD to SIG_IGN causes breaking wait and waitpid . In your example waitpid writes nothing to status variable (or writes trash).

182, 56, 163, 62, 51, etc..

This numbers are values of uninitialized integer variable (or trash).

As an alternative, I'm trying to use fork/exec/wait to execute my script

It is not good alternative. Alternative solution is set disposition of SIGCHLD to SIG_DFL for all parts of program. And change strategy of handling zombies in other parts.