wait child process but get error: 'pid is not a child of this shell'

Question

I write a script to get data from HDFS parrallel，then I wait these child processes in a for loop, but sometimes it returns "pid is not a child of this shell". sometimes, it works well。It's so puzzled. I use "jobs -l" to show all the jobs run in the background. I am sure these pid is the child process of the shell process, and I use "ps aux" to make sure these pids is note assign to other process. Here is my script.

PID=() FILE=() let serial=0  while read index_tar do         echo $index_tar | grep index > /dev/null 2>&1          if [[ $? -ne 0 ]]         then                 continue         fi          suffix=`printf '%03d' $serial`         mkdir input/output_$suffix         $HADOOP_HOME/bin/hadoop fs -cat $index_tar | tar zxf - -C input/output_$suffix \                 && mv input/output_$suffix/index_* input/output_$suffix/index &          PID[$serial]=$!         FILE[$serial]=$index_tar          let serial++  done < file.list  for((i=0;i<$serial;i++)) do         wait ${PID[$i]}          if [[ $? -ne 0 ]]         then                 LOG "get ${FILE[$i]} failed, PID:${PID[$i]}"                 exit -1         else                 LOG "get ${FILE[$i]} success, PID:${PID[$i]}"         fi done 

Answer 1

Just find the process id of the process you want to wait for and replace that with 12345 in below script. Further changes can be made as per your requirement.

#!/bin/sh PID=12345 while [ -e /proc/$PID ] do     echo "Process: $PID is still running" >> /home/parv/waitAndRun.log     sleep .6 done echo "Process $PID has finished" >> /home/parv/waitAndRun.log 

/usr/bin/waitingScript.sh

http://iamparv.blogspot.in/2013/10/unix-wait-for-running-process-not-child.html

Answer 2

Either your while loop or the for loop runs in a subshell, which is why you cannot await a child of the (parent, outer) shell.

Edit this might happen if the while loop or for loop is actually

(a) in a {...} block (b) participating in a piper (e.g. for....done|somepipe)