I have a process which can run one instance at a time. Currently we have multiple scripts trying to kickoff this process. I wanted to implement the semaphore mechanism to achieve this.
I was going through few examples. The below code seems to be reasonable solution.
But I am concerned about limitations, eg. we do not have much control on the filename (in the above case, "important")
Especially our team who maintains the application in Production are not experts.
Which technique (command) would you recommend (least errors and less experience to maintain)
Hi,
I have written below check lockfile script but need some tweaking on it.
If there is a lockfile from present, I need the script to retry every 10 seconds to see if the lockfile is still there. After 120 seconds it should send an email.
In my current version, if the script encounters... (6 Replies)
Just tried out the following code from "Using lockfiles in shell scripts":
#!/bin/bash
if ; then
echo "File exists"
else
echo "File does not exists. Create file now."
echo 1 > number.txt
fi
lockfile script.lock
a=$(/usr/bin/tail -n 1 number.txt)
if ; then... (1 Reply)
Hi all,
I have to test some user priviliges. The goal is to be sure that an unauthorized user can't restart some modules (ssh, mysql etc...).
I'm trying to automate it with a shell script but in same cases I got the syslog broadcast message.
Is there any way to simply get a return code... (3 Replies)
Hi,
I am new to this forum, could any one please help me to understand the LOCKFILE command with an example and what exactly it is used for and how it is used.
Thanks
Reshu289 (4 Replies)
Hello,
I have been working on using "flock"/file lock to prevent two instances of a bash script from being executed. Below is a simplified version of what I have to illustrate the flock part. It works as it is set up there below however the piece I am trying to figure out is how to get it to... (2 Replies)
I'm changing my mindset from a few big processes moving data from a few sources under an external, dependency-based scheduler to multiple processes moving data from many sources run by each client cron and possibly interfering with each other. It has the benefits of more granular code but I'm... (11 Replies)
Hi i have a script that check pings and i use flock to so the script wont run
multipul times :
its not the whole script but this is the idea :
(
flock -x -w 3 200 || exit 1
/usr/sbin/fping -c$count -i$interval -a $hosts > $FILE1 2>&1
) 200>/var/lock/.myscript.exclusivelock
now i... (4 Replies)
Discussion started by: batchenr
4 Replies
LEARN ABOUT SUSE
flock
FLOCK(1) H. Peter Anvin FLOCK(1)NAME
flock - Manage locks from shell scripts
SYNOPSIS
flock [-sxon] [-w timeout] lockfile [-c] command...
flock [-sxon] [-w timeout] lockdir [-c] command...
flock [-sxun] [-w timeout] fd
DESCRIPTION
This utility manages flock(2) locks from within shell scripts or the command line.
The first and second forms wraps the lock around the executing a command, in a manner similar to su(1) or newgrp(1). It locks a specified
file or directory, which is created (assuming appropriate permissions), if it does not already exist.
The third form is convenient inside shell scripts, and is usually used the following manner:
(
flock -s 200
# ... commands executed under lock ...
) 200>/var/lock/mylockfile
The mode used to open the file doesn't matter to flock; using > or >> allows the lockfile to be created if it does not already exist, how-
ever, write permission is required; using < requires that the file already exists but only read permission is required.
By default, if the lock cannot be immediately acquired, flock waits until the lock is available.
OPTIONS -s, --shared
Obtain a shared lock, sometimes called a read lock.
-x, -e, --exclusive
Obtain an exclusive lock, sometimes called a write lock. This is the default.
-u, --unlock
Drop a lock. This is usually not required, since a lock is automatically dropped when the file is closed. However, it may be
required in special cases, for example if the enclosed command group may have forked a background process which should not be hold-
ing the lock.
-n, --nb, --nonblock
Fail (with an exit code of 1) rather than wait if the lock cannot be immediately acquired.
-w, --wait, --timeout seconds
Fail (with an exit code of 1) if the lock cannot be acquired within seconds seconds. Decimal fractional values are allowed.
-o, --close
Close the file descriptor on which the lock is held before executing command. This is useful if command spawns a child process
which should not be hold ing the lock.
-c, --command command
Pass a single command to the shell with -c.
-h, --help
Print a help message.
AUTHOR
Written by H. Peter Anvin <hpa@zytor.com>.
COPYRIGHT
Copyright (C) 2003-2006 H. Peter Anvin.
This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICU-
LAR PURPOSE.
SEE ALSO flock(2)AVAILABILITY
The flock command is part of the util-linux-ng package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.
flock utility 4 Feb 2006 FLOCK(1)