Create a new independent process from another C process

Question

Two C executables A and B exist. A and B communicate to each other through a socket.

B can be started independently or through A.

1. If B is started first and A is started next, then A and B start properly without issues. Even if A is restarted, then there are no issues.

2. If B is started through A, then A and B starts properly. But here the communication port is bound to both A and B. Here, if A is restarted, then A fails to start.

Since B is started through A, Process A is the parent of Process B.

So, is there any means by which the Process B can be started independently from Process A?

We tried using fork, but with fork when we try to start the exe, two process is being started instead of one.

Answer 1

Have you tried using a 'wrapper' executable that forks off twice - once for A and once for B - and then kills itself? This would have A and B alive as separate processes that are then inherited by the init process, and should be safely restartable.

Answer 2

Are you sure you are checking correctly the return value of fork()?

Like:

pid_t pid;
if (pid == 0) {
    /* child */
}
else if (pid > 0) {
    /* parent */
}
else {
    /* error */
}

Answer 3

Are you using a Unix domain socket or a regular network socket?

Which of the processes, A or B, is listening on the socket (passive open), and which is doing the active open?

When you decide that A should run B, how does the code determine that this is necessary?

Are you opening the socket before you fork and exec?

My impression from the information given is:

• You use a network socket
• B is the listener

But I could easily be mistaken.

I wonder if you run into issues because A has already created the active socket before you fork and exec B, so the active end of the socket is not closed cleanly when A terminates because B has a copy of the socket open for writing as well as A. When you fork, the child process should clean up unneeded file descriptors (such as sockets) before executing another process.