Use of flock command for whole script Post: 302982536

Sponsored Content

Top Forums Shell Programming and Scripting Use of flock command for whole script Post 302982536 by Don Cragun on Thursday 29th of September 2016 03:47:37 PM

09-29-2016

Registered User

As long as you just have a single script that wants to be sure that only one copy of it is running at a time, you can use the shell's no clobber option to create a lock file something like:

Code:

#!/bin/bash
IAm=${0##*/}
LockFile="/tmp/$IAm.lock"

# Set lock and verify that no other copy of this code is already running...
set -C	# set no clobber option

# Create the lock file...  This will fail if the lock file already exists.
if ! echo "PID $$ holds the lock." > "$LockFile"
then	echo "$IAm: Another $IAm is already running." >&2
	cat "$LockFile" >&2
	echo "$IAm: Aborting!" >&2
	exit 1
fi

# We now hold an exclusive lock to the lock file (as long as other processes
# wanting to create this lock file also use set -C when trying to create this
# lock file).
set +C	# clear no clobber option

# Set up to remove the lock file when we're done.
trap 'rm -f "$LockFile"' EXIT

echo "$IAm: $$ running."
sleep 60
echo "$IAm: $$ quitting."

This should work with any POSIX conforming shell.

Just be aware that if you use kill -9 to kill this script, you'll have to manually remove the lock file before you can start another instance of this script.

These 2 Users Gave Thanks to Don Cragun For This Post:

Don Cragun

View Public Profile for Don Cragun

Find all posts by Don Cragun

7 More Discussions You Might Find Interesting

1. Shell Programming and Scripting

can anyone help with shell script command about searching word with grep command?

i want to search in the current directory all the files that contain one word for example "hello" i want to achieve it with the grep command but not with the grep *

2. Shell Programming and Scripting

Need help! command working ok when executed in command line, but fails when run inside a script!

Hi everyone, when executing this command in unix: echo "WM7 Fatal Alerts:", $(cat query1.txt) > a.csvIt works fine, but running this command in a shell script gives an error saying that there's a syntax error. here is content of my script: tdbsrvr$ vi hc.sh "hc.sh" 22 lines, 509...

3. Shell Programming and Scripting

SH script, variable built command fails, but works at command line

I am working with a sh script on a solaris 9 zone (sol 10 host) that grabs information to build the configuration command line. the variables Build64, SSLopt, CONFIGopt, and CC are populated in the script. the script includes CC=`which gcc` CONFIGopt=' --prefix=/ --exec-prefix=/usr...

4. UNIX for Advanced & Expert Users

Semaphore - lockfile/flock

Hi, 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. ...

5. Shell Programming and Scripting

Help using Flock (file lock)

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...

6. Shell Programming and Scripting

Flock preventing function to work

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...

7. Shell Programming and Scripting

Execute ssh command with additional terminal command to any remote user not working script

Hello i am having an issue with bash script and this is the code now=$(cat hosts1.txt | awk '{print $2;}') while read n ;do ssh root@$now 'useradd test1; echo -e "test1\ntest1" | passwd test1 && echo "test1 ALL=(ALL:ALL) ALL" >> /etc/sudoers' When i execute only part with cat, it...

LEARN ABOUT DEBIAN

explain_flock_or_die

explain_flock_or_die(3) 				     Library Functions Manual					   explain_flock_or_die(3)

NAME

       explain_flock_or_die - control advisory lock on open file and report errors

SYNOPSIS

       #include <libexplain/flock.h>
       void explain_flock_or_die(int fildes, int command);
       int explain_flock_on_error(int fildes, int command))

DESCRIPTION

       The  explain_flock_or_die  function is used to call the flock(2) system call. On failure an explanation will be printed to stderr, obtained
       from the explain_flock(3) function, and then the process terminates by calling exit(EXIT_FAILURE).

       The explain_flock_on_error function is used to call the flock(2) system call. On failure an explanation will be printed to stderr, obtained
       from the explain_flock(3) function, but still returns to the caller.

       fildes  The fildes, exactly as to be passed to the flock(2) system call.

       command The command, exactly as to be passed to the flock(2) system call.

RETURN VALUE

       The  explain_flock_or_die function only returns on success, see flock(2) for more information. On failure, prints an explanation and exits,
       it does not return.

       The explain_flock_on_error function always returns the value return by the wrapped flock(2) system call.

EXAMPLE

       The explain_flock_or_die function is intended to be used in a fashion similar to the following example:
	      explain_flock_or_die(fildes, command);

SEE ALSO

       flock(2)
	       apply or remove an advisory lock on an open file

       explain_flock(3)
	       explain flock(2) errors

       exit(2) terminate the calling process

COPYRIGHT

       libexplain version 0.52
       Copyright (C) 2009 Peter Miller

															   explain_flock_or_die(3)