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 HPUX
sem_trywait
sem_wait(2) System Calls Manual sem_wait(2)NAME
sem_wait, sem_trywait - lock a POSIX semaphore
SYNOPSIS DESCRIPTION
is used to lock a semaphore. The calling thread will not return from its call to until one of the following events occur: it successfully
obtains a lock on the semaphore; it is interrupted by a signal or an error condition occurs.
is used to lock a semaphore, if it is available. The value of the semaphore sem is checked at some unspecified time during the call. If
the semaphore is available at the time its value is checked, the calling thread will atomically, with respect to the checking of the value,
lock the semaphore. The thread will now own a lock on the semaphore; the call will return successfully. If the semaphore is unavailable
at the time its value is checked, then the call returns -1 with errno set to EAGAIN.
If the specified semaphore referred to by sem is a named semaphore, then this semaphore must have been opened by the calling process with
The calling process must have both read and write permissions on the semaphore to perform these operations. The semaphore will be locked
upon successful return and will stay locked until it is explicitly released by a call to
To use this function, link in the realtime library by specifying on the compiler or linker command line.
EXAMPLES
The following call to will lock the semaphore sem.
The following call to will lock the semaphore sem, if it is available.
RETURN VALUE
A successful call to will return 0 and the calling thread will then own a lock on the semaphore. Otherwise, the call to will return -1
with errno set to the appropriate value of the error condition.
A successful call to will return 0, if the semaphore was available and the calling thread was able to lock the semaphore. Otherwise, the
call to will return -1 with errno set to the appropriate value of the error condition.
ERRORS
and fail and do not perform the requested operation if any of the following conditions are encountered:
[EPERM] The calling process does not have the privileges necessary to lock the semaphore.
[EAGAIN] The semaphore was not available and hence could not be locked by This error condition only occurs in
[EINVAL] The argument sem does not refer to a valid semaphore.
[EINTR] The function was interrupted by a signal
SEE ALSO sem_post(2), <semaphore.h>.
STANDARDS CONFORMANCE sem_wait(2)