Either this or you create a semaphore file: consider the following script stub:
This makes sure the script runs only one instance at a time.
I hope this helps.
bakunin
Not quite. There is a race condition between the time the existence test ([ -e "$fSemaphore" ]) is executed and the time the semaphore file is created (touch "$fSemaphore") that can allow two or more copies of this code to run simultaneously and not realize that another invocation is running.
This can be worked around with the shell's do not clobber option:
Note that both of these run a risk of leaving the semaphore file in place if the script is terminated by a kill signal (for the code above) or by any signal (for the code bakunin suggested). If this happens, the semaphore file will have to be manually removed before the script will run again successfully.
I am in need of some help; think I have confused myself.
Here is the issue I am faced with.
The script log file was fine, the nohup.out file has tens of thousands of lines like illegal use of sleep: sleep seconds
So I assume there is something with the seconds calculation in the script... (1 Reply)
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Hi Forum
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i am very new to shall script . i am not that much aware of sleep command ,
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Hello,
Need a little help with the script below. I can't get it to sleep :( I'm trying to get this to check if the process is running and if it is, wait 10 secs and check again. Keep doing this until it's not running and then stop checking and send the email.
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I need to execute sleep command but i dont know the definite time.
Let me put my req:
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Discussion started by: pallvi_mahajan
15 Replies
LEARN ABOUT HPUX
msem_lock
msem_lock(2) System Calls Manual msem_lock(2)NAME
msem_lock() - lock a semaphore
SYNOPSIS DESCRIPTION
attempts to lock a binary semaphore.
sem points to an structure which specifies the semaphore to be locked.
If the semaphore is not currently locked, it becomes locked and the function returns successfully.
If the semaphore is currently locked, and condition is then the function returns with an error. If the semaphore is currently locked and
condition is zero, the function does not return until either the calling process is able to successfully lock the semaphore, or an error
condition occurs.
All calls to and by multiple processes sharing a common structure behave as if the calls were serialized.
If the structure contains any value not resulting from a call to followed by a (possibly empty) sequence of calls to and the results are
undefined. The address of an uniquely identifies the semaphore. If the structure contains any value copied from an structure at a differ-
ent address, the result is undefined.
IMPLEMENTATION NOTES
If blocked on a locked semaphore, suspends the calling process at a priority such that the process can be interrupted by a signal.
The system attempts to ignore or recover from invalid values written to the structure, but this is not guaranteed for all cases.
successfully acquires a semaphore that is locked by a process that has exited.
RETURN VALUE
returns one of the following values:
Success.
Failure.
is set to indicate the error.
ERRORS
sets to one of the following values if the corresponding condition is encountered.
was specified and the semaphore was already locked.
sem points to an structure that has been removed, or condition is invalid.
was interrupted by a signal that was caught.
The semaphore is currently locked,
condition is zero, and waiting to lock the semaphore would create a deadlock.
sem is not a properly aligned address or is otherwise an invalid pointer.
AUTHOR
was developed by HP and OSF.
SEE ALSO msem_init(2), msem_remove(2), msem_unlock(2), mman(5).
STANDARDS CONFORMANCE msem_lock(2)