Avoiding the second run of the script Post: 302570798

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Top Forums UNIX for Dummies Questions & Answers Avoiding the second run of the script Post 302570798 by jim mcnamara on Friday 4th of November 2011 10:41:37 AM

11-04-2011

Registered User

Your question confuses me a little. But the short answer is:

Create a lock file. This file has one single entry, the pid of the process running your script. If the file is "blank" then no script is running. If the file has a pid, but the pid (if it exists) is not running your script, then the previous version of the script crashed.

Make SURE you have only one place, one exit point for a succesful completion.

Put two entries the the file:
this one goes at the very beginning - this will work in ksh or bash:

Code:

export MYLOCKFILE=/path/to/mylockfile
[ ! -f  $MYLOCKFILE ]   &&  > $MYLOCKFILE    # create the file it it does not exist
pid=$(cat $MYLOCKFILE)
if [ -z  "$pid" ] ; then
   echo $$ > $MYLOCKFILE       # ok to run
else
   ps -ef | grep $pid | grep -q  $0  # see if this script is running
   if [ $? -eq 0 ] ; then   
         exit 1                        # error exit; another process is now running the script
   else
        echo ' this is a restart'
        echo $$ > $MYLOCKFILE       # ok to run
fi

one line before the one and only successful exit point:

Code:

echo "" > $MYLOCKFILE    # clear the lock

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LEARN ABOUT DEBIAN

service

service(8)						      System Manager's Manual							service(8)

NAME

       service - run a System V init script

SYNOPSIS

       service SCRIPT COMMAND [OPTIONS]

       service --status-all

       service --help | -h | --version

DESCRIPTION

       service	runs a System V init script in as predictable an environment as possible, removing most environment variables and with the current
       working directory set to /.

       The SCRIPT parameter specifies a System V init script, located in /etc/init.d/SCRIPT.  The  supported  values  of  COMMAND  depend  on  the
       invoked	script.  service passes COMMAND and OPTIONS to the init script unmodified.  All scripts should support at least the start and stop
       commands.  As a special case, if COMMAND is --full-restart, the script is run twice, first with the stop command, then with the start  com-
       mand.

       service --status-all runs all init scripts, in alphabetical order, with the status command.

EXIT CODES

       service calls the init script and returns the status returned by it.

FILES

       /etc/init.d
	      The directory containing System V init scripts.

ENVIRONMENT

       LANG, TERM
	      The only environment variables passed to the init scripts.

SEE ALSO

       /etc/init.d/skeleton,
       update-rc.d(8),
       init(8),
       invoke-rc.d(8).

								     Jan 2006								service(8)