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Full Discussion: Waiting for the background process to finish
Top Forums Shell Programming and Scripting Waiting for the background process to finish Post 302464105 by DGPickett on Tuesday 19th of October 2010 09:41:15 AM
Old 10-19-2010
Standard interview question, and actually, many variations on the answer. First, classic wait for specific job:

Code:
set -o bgnice off   # ksh thinks bg jobs are second class
Job_1&
pid_job_1=$!
Job_2&
pid_job_2=$!
 .
 .
 .
wait $pid_job_1
 .
 .
 .
wait $pid_job_2

You can also wait for all jobs with a barefoot wait. Check man ksh. When running a bare wait from the command line, be aware that it waits for other, unrelated jobs you ran from that terminal shell.

Also beware, the child processes will be done, but their descendents may still be running!

More sophisticated, and capable of monitoring all descendent processes:
Code:
(
job1 &
job2 &
) 2>&1 | cat -u >>$jobs_log

When every process inside the parentheses closes (or redirects) both stdout and stderr, the cat will end. You can use stdout for payload or logging, but generally, to keep the parent waiting, reserve one of the two for logging. Plus, you have an integrated log, always a nice idea.

You can also run fuser on the log files to see if any pid has it open. Of course, if someone has their vi nose in there, you will think it is still being written unless you check the pids with ps -fp $pid.
 

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LEARN ABOUT XFREE86

queuedefs

queuedefs(4)							   File Formats 						      queuedefs(4)

NAME

       queuedefs - queue description file for at, batch, and cron

SYNOPSIS

       /etc/cron.d/queuedefs

DESCRIPTION

       The queuedefs file describes the characteristics of the queues managed by cron(1M). Each non-comment line in this file describes one queue.
       The format of the lines are as follows:

	      q.[njobj][nicen][nwaitw]

       The fields in this line are:

       q	The name of the queue. a is the default queue for jobs started by at(1); b is the default queue for jobs  started  by  batch  (see
		at(1)); c is the default queue for jobs run from a crontab(1) file.

       njob	The  maximum  number of jobs that can be run simultaneously in that queue; if more than njob jobs are ready to run, only the first
		njob jobs will be run, and the others will be run as jobs that are currently running terminate.  The default value is  100.

       nice	The nice(1) value to give to all jobs in that queue that are not run with a user ID of super-user.  The default value is 2.

       nwait	The number of seconds to wait before rescheduling a job that was deferred because more than njob jobs were running in  that  job's
		queue, or because the system-wide limit of jobs executing has been reached.  The default value is 60.

       Lines beginning with # are comments, and are ignored.

EXAMPLES

       Example 1: A sample file.

       #
       #
       a.4j1n
       b.2j2n90w

       This  file  specifies that the a queue, for at jobs, can have up to 4 jobs running simultaneously; those jobs will be run with a nice value
       of 1.  As no nwait value was given, if a job cannot be run because too many other jobs are running cron will wait 60 seconds before  trying
       again to run it.

       The  b  queue, for batch(1) jobs, can have up to 2 jobs running simultaneously; those jobs will be run with a nice(1) value of 2.  If a job
       cannot be run because too many other jobs are running, cron(1M) will wait 90 seconds before trying again to run it. All	other  queues  can
       have up to 100 jobs running simultaneously; they will be run with a nice value of 2, and if a job cannot be run because too many other jobs
       are running cron will wait 60 seconds before trying again to run it.

FILES

       /etc/cron.d/queuedefs	       queue description file for  at, batch, and  cron.

SEE ALSO

       at(1), crontab(1), nice(1), cron(1M)

SunOS 5.10							    1 Mar 1994							      queuedefs(4)
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