With any POSIX-conforming shell, you can also use:
This works to guarantee that only one process holds the lock (assuming that lockfile is an absolute pathname), but the read could fail if the lock was held at the time you requested the lock but the lock holder terminated before the read was processed. (So, you need to verify that the read worked rather than assume that it will always succeed.)
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 DEBIAN
dotlock
dotlock(1) Mail Avenger 0.8.3 dotlock(1)NAME
dotlock - execute a command with a lock on a mailbox
SYNOPSIS
dotlock [-LPW] mbox-file command [arg ...]
DESCRIPTION
dotlock acquires a lock on the mailbox file mbox-file using both flock and a lock file, then executes command with any arguments specified.
When command exits, dotlock releases the lock.
dotlock attempts to clean up stale lockfiles. If it succeeds in locking an mbox-file with flock, and roughly 30 seconds elapse without
there being any changes to mbox-file or the lockfile, then dotlock will delete the lockfile and try again.
While it holds a lock, lockfile will keep updating the modification time of the lockfile every 15 seconds, to prevent the lock from getting
cleaned up in the event that command is slow.
OPTION
--noflock (-L)
Ordinarily, dotlock uses both flock and dotfile locking. (It uses flock first, but releases that lock in the even that dotfile locking
fails, so as to avoid deadlocking with applications that proceed in the reverse order.) The -L option disables flock locking, so that
dotlock only uses dotfile locking.
This is primarily useful as a wrapper around an application that already does flock locking, but to which you want to add dotfile
locking. (Even if your mail delivery system doesn't use flock, flock actually improves the efficiency of dotlock, so there is no
reason to disable it.)
--fcntl (-P)
This option enables fcntl (a.k.a. POSIX) file locking of mail spools, in addition to flock and dotfile locking. The advantage of fcntl
locking is that it may do the right thing over NFS. However, if either the NFS client or server does not properly support fcntl
locking, or if the file system is not mounted with the appropriate options, fcntl locking can fail in one of several ways. It can
allow different processes to lock the same file concurrently--even on the same machine. It can simply hang when trying to acquire a
lock, even if no other process holds a lock on the file. Also, on some OSes it can interact badly with flock locking, because those
OSes actually implement flock in terms of fcntl.
--nowait (-W)
With this option, dotlock simply exits non-zero and does not run command if it cannot immediately acquire the lock.
SEE ALSO avenger(1), deliver(1), avenger.local(8)
The Mail Avenger home page: <http://www.mailavenger.org/>.
BUGS
dotlock does not perform fcntl/lockf-style locking by default. Thus, if your mail reader exclusively uses fcntl for locking, there will be
race conditions unless you specify the --fcntl option.
flock does not work over network file systems. Thus, because of dotlock's mechanism for cleaning stale lock files, there is a possibility
that a network outage could lead to a race condition where the lockfile is cleared before command finishes executing. If lockfile detects
that the lock has been stolen, it prints a message to standard error, but does not do anything else (like try to kill command).
AUTHOR
David Mazieres
Mail Avenger 0.8.3 2012-04-05 dotlock(1)