[KSH/Bash] Starting a parent process from a child process? Post: 302408483

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Top Forums Shell Programming and Scripting [KSH/Bash] Starting a parent process from a child process? Post 302408483 by alister on Monday 29th of March 2010 03:46:53 PM

03-29-2010

Registered User

Quote:

Originally Posted by bakunin

Start the scripts in background and with "nohup". see the man page of "nohup" for details.

If you start them this they will no longer stop when the parent process is killed.

That probably won't help, unless the controlling terminal is lost or a SIGHUP is being sent with kill. I assume that he's using either ^C (SIGINT) at the keyboard or a typical kill command (SIGTERM); nohup will not prevent a process from receiving either of these.

Your pid file suggestion is a good one though. Something along the lines of:

Code:

$ cat a.sh
#!/bin/sh

echo $$ > a.pid
./b.sh &
#Do whatever script a is supposed to do


$ cat b.sh
#!/bin/sh

echo $$ > b.pid
./c.sh &
# Do whatever script b is supposed to do


$ cat c.sh
#!/bin/sh

# Do whatever script c is suposed to do
kill $(cat a.pid b.pid)
# Make needed changes
./a.sh &

Although any external executables running asynchronously at the time that the parent shell receives SIGTERM from kill will linger until they're done. If that's an issue, then a.sh would need to be started asynchronously and any signals sent to its process group (which b, c, a, b ... and further iterations in the cycle would inherit).

Regards,
Alister

Last edited by alister; 03-29-2010 at 05:32 PM..

alister

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LEARN ABOUT MINIX

fork

FORK(2) 							System Calls Manual							   FORK(2)

NAME

       fork - create a new process

SYNOPSIS

       #include <sys/types.h>
       #include <unistd.h>

       pid_t fork(void)

DESCRIPTION

       Fork causes creation of a new process.  The new process (child process) is an exact copy of the calling process except for the following:

	      The child process has a unique process ID.

	      The child process has a different parent process ID (i.e., the process ID of the parent process).

	      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 an lseek(2) 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.

	      The child starts with no pending signals and an inactive alarm timer.

RETURN VALUE

       Upon successful completion, fork 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.

ERRORS

       Fork will fail and no child process will be created if one or more of the following are true:

       [EAGAIN]       The system-imposed limit on the total number of processes under execution would be exceeded.  This limit	is  configuration-
		      dependent.  (The kernel variable NR_PROCS in <minix/config.h> (Minix), or <minix/const.h> (Minix-vmd).)

       [ENOMEM]       There is insufficient (virtual) memory for the new process.

SEE ALSO

       execve(2), wait(2).

3rd Berkeley Distribution					   May 22, 1986 							   FORK(2)

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