I have a small function that I use to see if another version of the script is currently running. Occasionally, about 10% of the time, it reports that two instances of the script are currently running. Since I am using a unique name, I know that there is not another version running out there by another user.

I created a test script to capture some data. It appears as though "ps" is occasionally spawning a child shell. I have run the same test script on other AIX servers and have not been able to repeat it on them.

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AIX LEVEL
**********
/tmp>/usr/bin/rpm -qa | grep AIX
AIX-rpm-5.2.0.40-1

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TEST SCRIPT
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#!/usr/bin/sh
function p_check
{
PGM=$1
##myCNT=$(ps -ef | tee junk | grep -v grep | grep -c $PGM)
myCNT=$(ps -ef | tee junk | grep $PGM | grep -v grep | wc -l | awk '{print $1}')
rc=$?

if [[ $myCNT != "1" ]]; then
echo "$PGM is already running.($myCNT)"
echo "rc = $rc"
exit 100
fi
}

p_check "checkPS2.sh"


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OUTPUT FROM SCRIPT
********************
tmp>checkPS2.sh
tmp>checkPS2.sh
tmp>checkPS2.sh
checkPS2.sh is already running.(2)
rc = 0


************************************
SEARCH OF OUTPUT FILE (when problem occurs)
************************************
tmp>grep checkPS junk
edat 10618 36204 1 09:50:57 pts/0 0:00 /usr/bin/sh checkPS2.sh
edat 36204 17852 1 09:50:57 pts/0 0:00 /usr/bin/sh checkPS2.sh
edat 51188 10618 0 09:50:57 pts/0 0:00 grep checkPS2.sh

tmp>grep pts\/0 junk
UID PID PPID C STIME TTY TIME CMD
edat 17852 28470 0 15:36:44 pts/0 0:00 -ksh
edat 36204 17852 1 09:50:57 pts/0 0:00 /usr/bin/sh checkPS2.sh
edat 10618 36204 1 09:50:57 pts/0 0:00 /usr/bin/sh checkPS2.sh
edat 48266 10618 0 09:50:57 pts/0 0:00 tee junk
edat 51188 10618 0 09:50:57 pts/0 0:00 grep checkPS2.sh
edat 16540 10618 3 09:50:57 pts/0 0:00 ps -ef

******************************************
SEARCH OF OUTPUT FILE (when problem does not occur)
******************************************
tmp>grep pts\/0 junk
edat 17852 28470 1 15:36:44 pts/0 0:00 -ksh
edat 50054 17852 1 10:20:01 pts/0 0:00 /usr/bin/sh checkPS2.sh
edat 50400 50054 0 10:20:01 pts/0 0:00 awk {print $1}
edat 52060 50400 0 10:20:01 pts/0 0:00 tee junk
edat 48634 50400 0 10:20:01 pts/0 0:00 grep checkPS2.sh
edat 48354 50400 4 10:20:01 pts/0 0:00 ps -ef

We updated the libc.a library to match that of the other servers but that did not resolve the problem.

Am I simply facing a race condition here or is there more than meets the eye?

Thanks in advance.