12-16-2014
How to wait for a grand child to finish?
Hello all,
I have a very basic question. I have a requirement where in, I have a main process which forks a child process, which execs and runs a c executable corresponding to a daemon. In the c executable corresponding to a daemon, as everyone does, I fork another child process, and as part of child, run the daemon functionality by its parent exiting, so that the child(daemon) becomes a child of init. Now, from the main process(grand parent), I would like to wait for the daemon process(grand child).
Just to explain more clearly, I have a process p1, which forks a new process p2. In p2 functionality, I fork another process p3 which execs and runs a daemon, p2 exits to make p3 a child of init. Now, from p1, I want to wait for p3. I can not use waitpid in the grand parent process to wait for the grand child I believe. How to proceed?
I would be very glad if you can help me.
Thanks in advance,
Sai
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fork(2) System Calls Manual fork(2)
Name
fork - create a new process
Syntax
#include <sys/types.h>
#include <unistd.h>
pid = fork()
pid_t pid;
Description
The system call causes creation of a new process. The new process (child process) is an exact copy of the calling process except for the
following:
o The child process has a unique process ID.
o The child process has a different parent process ID (that is, the process ID of the parent process).
o The child process has its own copy of the parent's descriptors. These descriptors reference the same underlying objects, so that, for
instance, file pointers in file objects are shared between the child and the parent, so that a on a descriptor in the child process
can affect a subsequent read or write by the parent. This descriptor copying is also used by the shell to establish standard input
and output for newly created processes as well as to set up pipes.
o The child processes resource utilizations are set to 0. For further information, see
Return Values
Upon successful completion, returns a value of 0 to the child process and returns the process ID of the child process to the parent
process. Otherwise, a value of -1 is returned to the parent process, no child process is created, and the global variable errno is set to
indicate the error.
Diagnostics
The system call fails and no child process are created under the following conditions:
[EAGAIN] The system-imposed limit {PROC_MAX} on the total number of processes under execution would be exceeded.
[EAGAIN] The system-imposed limit {CHILD_MAX} on the total number of processes under execution by a single user would be exceeded.
[ENOMEM] There is insufficient swap space for the new process.
See Also
execve(2), wait(2)
fork(2)