Date: Fri, 22 Jul 2011 12:10:37 +0000 From: Alexander Best <arundel@freebsd.org> To: "C. P. Ghost" <cpghost@cordula.ws> Cc: Unga <unga888@yahoo.com>, freebsd-questions@freebsd.org Subject: Re: How to sync a file on FreeBSD? Message-ID: <20110722121037.GA98992@freebsd.org> In-Reply-To: <CADGWnjU3puwc5k8ab33FK-6Z=oimxQJWHCJdgN-yQKpSJdWS-g@mail.gmail.com> References: <1311317040.38368.YahooMailClassic@web160115.mail.bf1.yahoo.com> <CADGWnjU3puwc5k8ab33FK-6Z=oimxQJWHCJdgN-yQKpSJdWS-g@mail.gmail.com>
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On Fri Jul 22 11, C. P. Ghost wrote: > On Fri, Jul 22, 2011 at 8:44 AM, Unga <unga888@yahoo.com> wrote: > > Hi all > > > > How to sync a file on FreeBSD (esp. on 8.1) to disk? > > > > I used fsync(2), but does not immediately flush to disk. > > > > I want my writing to a file (a log file) immediately available to other users to read. if you *really* want to see data being written to disk immediately and don't care about performance, do the following: 1) disable the write cache of your hdd (see ada(4) and ata(4) man pages) 2) mount your partition(s) with '-o sync' cheers. alex > > It shouldn't matter: as soon as write(2) completes, the > system-wide file cache -- not the disk -- is updated, and > other users will transparently read(2) from that cache, > not from the disk. > > What you probably want is to flush the userspace buffers > of your I/O library as soon as you write a line of output: > See fflush(3), set[v]buf(3)... You may also use a non-buffered > stream for writing logs. > > fsync(2) has other uses. In particular, it is of NO use as > long as the logging application doesn't flush its I/O caches > itself. > > > Best regards > > Unga > > -cpghost. > > -- > Cordula's Web. http://www.cordula.ws/
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