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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 302989646 by Aia on Monday 16th of January 2017 08:42:40 PM
Old 01-16-2017
Quote:
Originally Posted by Chubler_XL
You could try using a .pid file and check it at the top of your script like this:

Code:
#!/bin/sh

NAME=$(basename "$0")

if [ -f /var/run/"$NAME.pid" ] &&
  ps -p $(cat /var/run/"$NAME.pid") >/dev/null 2>&1
then
   echo "Script is currently in progress..aborting..."
   exit 3
fi

trap 'rm -f /var/run/"$NAME.pid"' EXIT
echo $$ > /var/run/"$NAME.pid"

...

All designs that try to check for a lock-file or pid-file are flawed. They are subjective to racecondition
The problem is that you can not check for the existence of a file and the creation of that file in an atomic action. And in between of those two actions another instance can run.

Some more info
Last edited by Aia; 01-16-2017 at 10:02 PM..
These 2 Users Gave Thanks to Aia For This Post:
Chubler_XL SkySmart
 

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LEARN ABOUT NETBSD

screenblank

SCREENBLANK(1)						    BSD General Commands Manual 					    SCREENBLANK(1)

NAME

     screenblank -- screen saver daemon for wscons and FBIO machines

SYNOPSIS

     screenblank [-k | -m] [-d inactivity-timeout] [-e wakeup-delay] [-f framebuffer] [-i input-device]
     screenblank {-b | -u}

DESCRIPTION

     screenblank disables the framebuffer if the keyboard and mouse are idle for a period of time, and re-enables the framebuffer when keyboard or
     mouse activity resumes.

     When killed with a SIGINT, SIGHUP, or SIGTERM, screenblank will re-enable the framebuffer.  The pid can be found in the file
     /var/run/screenblank.pid.

     The options are as follows:

     -b      Overriding the other options, simply try (once) to blank the framebuffer, then exit.

     -d inactivity-timeout
	     Wait the number of seconds specified by inactivity-timeout, expressed in the format ``xxx.xxx'', before disabling the framebuffer due
	     to inactivity.  The default is 600 seconds (10 minutes).

     -e wakeup-delay
	     Wait the number of seconds specified by wakeup-delay, expressed in the format ``xxx.xxx'', before re-enabling the framebuffer once
	     activity resumes.	The default is .25 seconds.

     -f framebuffer
	     Use the framebuffer device framebuffer instead of the default /dev/fb.

     -i input-device
	     Add input-device to the list of devices to monitor for activity.

     -k      Do not check the keyboard for activity.

     -m      Do not check the mouse for activity.

     -u      Overriding the other options, simply try (once) to unblank the framebuffer, then exit.

     Note that the -k and -m flags are mutually exclusive.

FILES

     /dev/kbd			 The keyboard device.

     /dev/mouse 		 The mouse device.

     /dev/console		 The console device.

     /dev/fb			 The default framebuffer.

     /dev/wskbd 		 The keyboard for wscons machines.

     /dev/wsmouse		 The mouse device for wscons machines.

     /dev/ttyE0 		 The console device for wscons machines.

     /var/run/screenblank.pid	 File containing the pid of screenblank.

BSD
								September 23, 2006							       BSD
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