Questions about IPC Post: 303012046

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Top Forums UNIX for Beginners Questions & Answers Questions about IPC Post 303012046 by jim mcnamara on Sunday 28th of January 2018 12:59:45 PM

01-28-2018

Registered User

You have assumptions you may not realize that you have.

When a parent creates a child
1. if the child "stays" as a child it can communicate to the parent via pipes, shared memory - ipc in general is possible. Sometimes the child stdout is the parent's same stdout (shared) with the parent. There no requirement that it be done one way or another. The parent should call wait() on the child process and then take correct action depending on the return from the child (exit()).

2. The child calls setsid() and becomes the head of its very own process. It can still talk to the parent if it is coded to do that, but when the process ends, the parent has gone on to do other things and had not called wait() on the child.

3. a daemon is a special version of #2. The child turns off connections to stdin, stdout, stderr. These processes are often called services. Normally they do not engage in IPC with the parent.

4. Sometimes a child can be #1, #2, or #3 but it uses signals to/from the parent to interoperate.

Shells mostly use #1 - you type the ls command, it does it's thing, writes to stdout, then calls exit. The status of the child is available to the parent shell in the $? variable.

I've simplified this for understanding. Someone else may not feel my choices were the best. In any event - You should really consider learning what https://www.tldp.org/LDP/tlk/ipc/ipc.html has to say. And learn it reasonably well.

jim mcnamara

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create_child

create child(1m)														  create child(1m)

NAME

       create child - Creates a child pointer at the master replica of the parent directory

SYNOPSIS

       cdscp create child child-name clearinghouse clearinghouse-name

ARGUMENTS

       The full name of the child pointer.  The full name of a clearinghouse that contains a replica of the child directory.

DESCRIPTION

       The create child command creates a child pointer at the master replica of the parent directory.	When CDS looks up a name in the namespace,
       it uses child pointers to locate directory replicas.  Use the set cdscp preferred clearinghouse command	before	issuing  this  command	to
       ensure that the request is directed to the master replica.

   Privilege Required
       You must have insert permission to the parent directory.

NOTES

       Use  the  create  child	command  only  to  re-create a child pointer that is accidentally deleted. This command is designed only for trou-
       bleshooting.

       This command will fail if the associated directory does not exist.  If the associated directory exists, this command will  return  success-
       fully.

       This command is replaced at Revision 1.1 by the dcecp command and may not be provided in future releases of DCE.

EXAMPLE

       The  following  command	creates the child pointer in the parent directory /.:/subsys.  It uses the replica located at the /.:/subsys/NY_CH
       clearinghouse to fill in its replica set.

       cdscp> create child /.:/subsys clearinghouse /.:/subsys/NY_CH

RELATED INFORMATION

       Commands: delete child(1m), list child(1m), show child(1m)

																  create child(1m)

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