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From: dce@smsc.sony.com (David Elliott)
Newsgroups: comp.unix.questions
Subject: Re: How to flush output to disk?
Keywords: flush buffer disk
Message-ID: <1989Dec6.211440.20629@smsc.sony.com>
Date: 6 Dec 89 21:14:40 GMT
References: <606@caldwr.UUCP> <1025@friar-taac.UUCP>
Reply-To: dce@Sony.COM (David Elliott)
Distribution: na
Organization: Sony Microsystems Corp.
Lines: 28

In article <1025@friar-taac.UUCP> matthew@friar-taac.UUCP (Matthew Stier - Sun Visualization Products) writes:
>In article <606@caldwr.UUCP> rfinch@caldwr.UUCP (Ralph Finch) writes:
>>
>>Is there any way to force the output to be flushed more often, say every 15-30 minutes?
>
>The following, untested, script should do it. (I know using 'sync' is a little heavy 
>handed, but it gets the job done.)

Are we talking about the same thing?

Maybe SunOS changed this, but on most BSD systems, the disk buffers are
written every 30 seconds via the /etc/update command.  Even if they
weren't, when you open a file that someone has written to, you get
pages from the buffer cache first, so you should get the data.

The problem here is (probably) that Ralph's program is using stdio to
log its output, and since the data is going to a file, it gets buffered
inside the program.  In other words, the data hasn't even gotten
written yet.

The easiest way to fix this is to modify the program to either call
fflush() at certain intervals to force the buffers to be written, or
call setlinebuf() (or the equivalent) to force line-buffered output.
-- 
David Elliott
dce@smsc.sony.com | ...!{uunet,mips}!sonyusa!dce
(408)944-4073
"It's bigger than a breadbox, and smaller than the planet Jupiter."