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Top Forums Shell Programming and Scripting No lock file: Preventing multiple instance of a script Post 302574628 by McFadden586 on Thursday 17th of November 2011 06:50:17 PM
Old 11-17-2011
No lock file: Preventing multiple instance of a script

I've been bitten by using a lock or pid file to prevent multiple instances of a script. A user typed kill -9, and the pid file didn't go away. You can't trap -9. So when he tried to restart, it said "already running", and I got trouble report. Argh.

So here's what we came up with:
Code:
# Stop if a previous version of this script is still running
ps | grep $0 | grep -v grep > /var/tmp/$0.pid
pids=$(cat /var/tmp/$0.pid | cut -d ' ' -f 1)
for pid in $pids
do
   if [ $pid -ne $$ ]; then
      logprint "$0 is already running. Exiting"
      exit 7
   fi
done
rm -f /var/tmp/$0.pid

It does use a temp file, but leaves no potential artifact to mess us up later.

If you try this without a temp file, you'll end up with a false positive because
pids=$(ps | grep $0 | grep -v grep | cut -d ' ' -f 1)
seems to leave it's own extra pid.

Last edited by Scott; 11-17-2011 at 09:43 PM.. Reason: Please use code tags
 

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UUIDD(8)						       System Administration							  UUIDD(8)

NAME
uuidd - UUID generation daemon SYNOPSIS
uuidd [options] DESCRIPTION
The uuidd daemon is used by the UUID library to generate universally unique identifiers (UUIDs), especially time-based UUIDs, in a secure and guaranteed-unique fashion, even in the face of large numbers of threads running on different CPUs trying to grab UUIDs. OPTIONS
-d, --debug Run uuidd in debugging mode. This prevents uuidd from running as a daemon. -F, --no-fork Do not daemonize using a double-fork. -k, --kill If currently a uuidd daemon is running, kill it. -n, --uuids number When issuing a test request to a running uuidd, request a bulk response of number UUIDs. -P, --no-pid Do not create a pid file. -p, --pid path Specify the pathname where the pid file should be written. By default, the pid file is written to /run/uuidd/uuidd.pid. -q, --quiet Suppress some failure messages. -r, --random Test uuidd by trying to connect to a running uuidd daemon and request it to return a random-based UUID. -S, --socket-activation Do not create a socket but instead expect it to be provided by the calling process. This implies --no-fork and --no-pid. This option is intended to be used only with systemd(1). It needs to be enabled with a configure option. -s, --socket path Make uuidd use this pathname for the unix-domain socket. By default, the pathname used is /run/uuidd/request. This option is pri- marily for debugging purposes, since the pathname is hard-coded in the libuuid library. -T, --timeout number Make uuidd exit after number seconds of inactivity. -t, --time Test uuidd by trying to connect to a running uuidd daemon and request it to return a time-based UUID. -V, --version Output version information and exit. -h, --help Display help screen and exit. EXAMPLE
Start up a daemon, print 42 random keys, and then stop the daemon: uuidd -p /tmp/uuidd.pid -s /tmp/uuidd.socket uuidd -d -r -n 42 -s /tmp/uuidd.socket uuidd -d -k -s /tmp/uuidd.socket AUTHOR
The uuidd daemon was written by Theodore Ts'o <tytso@mit.edu>. SEE ALSO
uuid(3), uuidgen(1) AVAILABILITY
The uuidd daemon is part of the util-linux package and is available from the Linux Kernel Archive <https://www.kernel.org/pub/linux/utils /util-linux/>. util-linux July 2014 UUIDD(8)
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