file busy

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From - Wed Nov  8 06:23:41 2000
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Newsgroups: comp.unix.sco.misc
Subject: Re: knowing when a file is busy?
References: <u71ywnqw90.fsf@benburb.tangent.com> 
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From: spcecdt@deeptht.armory.com. (John DuBois)
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In article <u71ywnqw90.fsf@benburb.tangent.com>,
joe mc cool  <joe@benburb.demon.co.uk> wrote:
>How can I be sure that the application has finished writing to the end 
>of the file before I grab it ?  Cron would check every minute, say,
>and if the file existed it would send it to the printer and then erase 
>it.  Of course I could rename the file before printing it.  But does
>that guarantee that I won't loose data ?  What is the safe approach ?

You need a combination of approaches.  First, rename the file; then, use fuser
or lsof in a loop to check whether the file is open.  Open file descriptors
won't be affected by the renaming, so if anything is writing to the file it
will continue writing.  Once the file is no longer open, print it and remove it
(arrange for both at once with lp -R).  Note that you need to be root to use
fuser.

        John
-- 
John DuBois  spcecdt@armory.com.  KC6QKZ/AE  http://www.armory.com./~spcecdt/

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