<div dir="ltr">I would agree, except that Alex indicated that noatime causes the correct behavior. </div><div class="gmail_extra"><br><br><div class="gmail_quote">On Wed, Dec 4, 2013 at 11:24 PM, Brian O'Neill <span dir="ltr"><<a href="mailto:oneill@oinc.net" target="_blank">oneill@oinc.net</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div>I'm thinking the atime is being updated by the server because the server accessed the file in order to serve it...<br>
<br><div class="gmail_quote">Alex Aminoff <<a href="mailto:alex@basespace.net" target="_blank">alex@basespace.net</a>> wrote:<blockquote class="gmail_quote" style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<pre><div><div class="h5">On 12/4/2013 10:21 PM, Matt Simmons wrote:<br><blockquote class="gmail_quote" style="margin:0pt 0pt 1ex 0.8ex;border-left:1px solid #729fcf;padding-left:1ex">My knowledge is somewhat limited to the Linux world, but in my <br>
experience I've never seen a mount be set to 'ro' and have anything <br>updated. I hate to use the term 'flabbergasted', but I'm pretty sure <br>that if I saw an implementation that didn't respect the 'ro' flag, I'd <br>
be at the very least 'put out', and perhaps even vitriolic.</blockquote><br>Yeah, flabbergasted is a good description of how I felt.<br><br>Nevertheless, I tested it and unless I messed up my test, an NFS mount <br>
with -o ro, you read a file on the mounted FS, and the access time is <br>updated.<br><br>For the test the server was a NetApp, the client was Linux.<br><br>There is a mount flag -o noatime that does what I want. But I would <br>
argue that this is not right. The simplest be
havior
- nothing is ever <br>written period - should be what you get by default, and then there could <br>be a flag that enables exceptional behavior, that is updating the access <br>time.<br><br>I can squint and see why it would be the way it is. One perspective is <br>
that the naive assumption is that reading off a RO filesystem should be <br>just like reading any other way; when you read, the OS conveniently <br>remembers when you did. The inconsistency of "writing" to a read-only <br>
thing is less important than the inconsistency of not updating the <br>access time when the file is read.<br><br>But what if the underlying device is not capable of recording access <br>times, like a CD-ROM? Can you look at the mount options and see that a <br>
CDROM is read-only? But then you can't know whether access times will be <br>updated unless you use some other method to find out what the underlying <br>device is. So that's an abstraction violation. Bother, I
don't
have a <br>unix box easily to hand where I can check what the mount options on a <br>CDROM look like.<br><br>I'm not sure if this is just grousing, or flame bait, or a gotcha that <br>every sysadmin should know because there is no way to anticipate it.<br>
<br>- Alex<br><br></div></div><blockquote class="gmail_quote" style="margin:0pt 0pt 1ex 0.8ex;border-left:1px solid #729fcf;padding-left:1ex"><div><div class="h5">--Matt<br><br><br><br>On Tue, Dec 3, 2013 at 2:21 PM, Alex Aminoff <<a href="mailto:alex@basespace.net" target="_blank">alex@basespace.net</a> <br>
<mailto:<a href="mailto:alex@basespace.net" target="_blank">alex@basespace.net</a>>> wrote:<br><br><br>Hi folks. I encountered something odd.<br><br>Suppose you mount a file system read only. You read a file from<br>
it. Does<br>the access time of that file get updated?<br><br>In one place I found documentation saying no. But other places seem to<br>imply that it does.<br><br>Does the answer change if it is an NFS mount?<br><br>I have deliberately left details of what OS I'm using out, becau
se
it<br>seems to me that the answer should be consistent, and if it is not, it<br>should be documented publicly.<br><br>- Alex Aminoff<br><a href="http://BaseSpace.net" target="_blank">BaseSpace.net</a>, NBER<br><br><br><br>
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