ksh script - Preventing multiple runs of a particular script

[Melissa]

I am having trouble with a ksh script I am writing. I need to make
sure that the script is not already running when it is kicked off in
cron. When I run the scripts manually, I do not have a problem.
However, when cron runs the scripts, well, on occassion, it seems that
more than one instance of the process is running. The odd part is
that the output is creating only one log file and has only one
instance of the run.

I was hoping that someone would take some time to look over my script
and make some suggestions:

myScript.ksh
================================================== ====

#!/usr/bin/ksh

echo "Start Time: `date` "
echo

.. /opt/appl/batchftp/29g/29g_env

process=`ps -ef | grep $0 | grep -v grep | wc -l`

if [ process -gt 2 ]
then
echo "Script is already running. Wait for next run."
else
/opt/appl/batchftp/29g/runJava DownloadPOReceiptZATC
fi

echo
echo "End Time: `date` "
================================================== =

I have tried using the following as well:

myScript2.ksh
================================================== =
#!/usr/bin/ksh

# set -o xtrace

echo "Start Time: `date` "
echo

.. /opt/appl/batchftp/29g/29g_env

set -o xtrace

ps -ef | grep $0 | grep batchftp | grep -v grep

process=$(ps -ef | grep $0 | grep batchftp | grep -v grep)

if [ $(echo $process | /usr/bin/wc -l) -gt 1 ]
then
echo "Script is already running. Wait for next run."
else
/opt/appl/batchftp/29g/runJava DownloadPOReceiptZDIR
fi

echo
echo "End Time: `date` "
================================================== ===

Any suggestions you may have would be greatly appreciated!

Thanks!

Melissa

[Davide Bianchi]

Melissa <melissa_2114@yahoo.com> wrote:

> more than one instance of the process is running.

I'd use a lock file approach, something like creating a file in
a well-know location when the script start and removing when the
script ends, and then checking if the file is already there before
starting the script.

> #!/usr/bin/ksh

if [ -f /var/run/signal.lock ] ; then
echo "lock file there"
exit 0
else
touch /var/run/signal.lock
fi

....rest of the script

> echo
> echo "End Time: `date` "

rm /var/run/signal.lock

Note: I'm not sure if the if/else syntax is correct for ksh.

Davide

[Andreas Kahari]

In article <bn8od3$u87p8$8@ID-18487.news.uni-berlin.de>, Davide Bianchi wrote:

> Melissa <melissa_2114@yahoo.com> wrote:

>> more than one instance of the process is running.

>
> I'd use a lock file approach, something like creating a file in
> a well-know location when the script start and removing when the
> script ends, and then checking if the file is already there before
> starting the script.
>

>> #!/usr/bin/ksh

>
> if [ -f /var/run/signal.lock ] ; then

# See if there is a process running with the PID that is stored
# in the lock file.
if kill -0 $(</var/run/signal.lock); then

> echo "lock file there"
> exit 0

else
echo "Found stale lock file"
fi

fi

> else

(remove "else")

> touch /var/run/signal.lock

Replace with:

# Put my PID into the lock file.
print $$ >/var/run/signal.lock

> fi

(remove "fi")

>
> ...rest of the script
>

>> echo
>> echo "End Time: `date` "

>
> rm /var/run/signal.lock
>
> Note: I'm not sure if the if/else syntax is correct for ksh.
>
> Davide

--
Andreas Kähäri

[Heiner Steven]

Andreas Kahari wrote:

> In article <bn8od3$u87p8$8@ID-18487.news.uni-berlin.de>, Davide Bianchi wrote:
>

>>Melissa <melissa_2114@yahoo.com> wrote:
>>

>>>more than one instance of the process is running.

I think there is no 100% way to implement this using
only shell scripts. This doesn't mean we cannot try
to make it as good as possible... ;-)

>>I'd use a lock file approach, something like creating a file in
>>a well-know location when the script start and removing when the
>>script ends, and then checking if the file is already there before
>>starting the script.

A lock file is one way, a symbolic link is another way to
indicate that the script is already running. Netscape/Mozilla
e.g. use an (invalid) symbolic link to the (ip address / process number)
a process is running on:

$ cd $HOME/.mozilla/default/*/
$ ls -l lock
lrwxrwxrwx 1 heiner users 14 2003-10-24 23:19 lock -> 127.0.0.2:4819

This means that the mozilla process is running on host with
ip address 127.0.0.2 (loop back address of my local host),
process id 4819:

$ ps -p 4819
PID TTY TIME CMD
4819 ? 00:02:50 mozilla-bin

In my opinion this is a very elegant way avoiding a file.

>>>#!/usr/bin/ksh

>>
>>if [ -f /var/run/signal.lock ] ; then

>
> # See if there is a process running with the PID that is stored
> # in the lock file.
> if kill -0 $(</var/run/signal.lock); then

>> echo "lock file there"
>> exit 0

> else
> echo "Found stale lock file"
> fi
>
> fi
>

>>else

>
> (remove "else")
>

>> touch /var/run/signal.lock

>
> Replace with:
>
> # Put my PID into the lock file.
> print $$ >/var/run/signal.lock

>>fi

>
> (remove "fi")
>

>>...rest of the script
>>

>>>echo
>>>echo "End Time: `date` "

>>
>>rm /var/run/signal.lock

The lock file should be removed by a "trap" handler, too.
This ensures that the lock file is removed when the script
receives a signal:

trap 'rm -f "$lockfile"' 0 # exit
trap "exit 2" 1 2 3 13 15 # HUP INT QUIT PIPE TERM

In a networked, multi-host environment it's important
to either create the lock file on a local file system
(e.g. /var/run), or (if the lock file may e.g. be NFS mounted)
include the IP address of the host setting the lock.
This is the way Mozilla handles it.

Heiner
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