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Full Discussion: Making sure only one instance of a script is running
Top Forums Shell Programming and Scripting Making sure only one instance of a script is running Post 302989738 by Chubler_XL on Tuesday 17th of January 2017 03:34:13 PM
Old 01-17-2017
Yes flock(1) is the right way to do this.

The OP is after a portable solution, so lets test for executable /usr/bin/flock
and use that when available but revert to the mkdir method on systems without it:

Code:
if [ -x /usr/bin/flock ] || [ -x /bin/flock ]
then
    # If the env var $FLOCKER is not set,  then execute flock and
    # grab an exclusive non-blocking lock (using the script
    # itself as the lock file) before re-execing itself with the right
    # arguments.   It also sets the FLOCKER env var to the right value
    # so it doesn't run again.  Otherwise exit with status 3

    [ "${FLOCKER}" != "$0" ] && 
        exec env FLOCKER="$0" flock -E 3 -en  "$0"  "$0" "$@" || :
else
    # Here, even when two processes call mkdir at the same time, 
    # only one process can succeed at most. This atomicity of 
    # check-and-create is ensured at the operating 
    # system kernel level.

    lockdir=/tmp/myscript.lock
    if mkdir "$lockdir"
    then
        # Remove lockdir when the script finishes, or when it receives a signal

        trap 'rm -rf "$lockdir"' 0    # remove directory when script finishes
    else
        exit 3
    fi
fi

These 2 Users Gave Thanks to Chubler_XL For This Post:
rbatte1 SkySmart
 

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LEARN ABOUT OSF1

uudemon.cleanu

uudemon(4)						     Kernel Interfaces Manual							uudemon(4)

NAME

       uudemon.admin,  uudemon.cleanu,	uudemon.hour,  uudemon.poll  -	Administrative shell scripts for polling remote systems, cleaning up spool
       directories, reporting status to the system administrator, and routine invocations of the uuxqt and uusched daemons

SYNOPSIS

       These shell scripts reside in the following directory:
	  /usr/lib/uucp

DESCRIPTION

       All the scripts can be run from the command line or can be run automatically by the cron daemon. To automatically run the  scripts,  remove
       the comment character (#) from the beginning of the relevant line in the /var/spool/cron/crontabs/uucp file.

       This  script  reports  status  to  the system administrator. It issues the uustat command to find out the status of uucp jobs. It mails the
       results to the uucp login ID. The script may be modified to send mail to any login ID such as the uucp administrative login ID  (uucpa)	or
       root.  This script cleans up the /var/spool/uucp and /var/spool/uucppublic directories by running the uucleanup command. The uucleanup com-
       mand is run with the following parameters: -C7, -D7, X2, -o2, -W1.  This script runs the uusched and uuxqt daemons in the background.  This
       script  polls  the  systems  listed  in	the  /usr/lib/uucp/Poll file.  The uudemon.poll script should be scheduled before the uudemon.hour
       script. This allows uudemon.poll to create any command files before cron runs the uudemon.hour script.

FILES

       Contains the uudemon.admin, uudemon.cleanu, uudemon.hour and uudemon.poll files.  Contains the uucp file.

RELATED INFORMATION

       Commands: cron(8), uucleanup(8), uusched(8), uuxqt(1)

       Files: /usr/lib/uucp delim off

																	uudemon(4)
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