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From: #! /shell/nerd on 11 Mar 2010 14:07
On Mar 3, 7:39 am, Geoff Clare <ge...(a)clare.See-My-Signature.invalid>
wrote:
> #! /shell/nerd wrote:
> >> > > And I have 10 such JVMs in a machine so they all simultaneously try to
> >> > > write to this file at one instance. Now I found that Atleast one is
> >> > > missed during the simulataneous write at the beginning e.g. JVM08
> >> > > might not be able to get a chance to put it's entry in the file.
> >> Before starting any JVM, In it's own process I'm doing printf "JVMXX
> >> \n" >> /tmp/out
> >> So each JVM writes to the file first & then continues with the start.
>
> > I'd appreciate if somebody could suggest anything !!
>
> What shell are you executing that printf in?  If it is not a
> POSIX-conforming shell then it's possible that it is implementing ">>"
> by just seeking to the end of the file instead of setting O_APPEND on
> the file descriptor.
>
> --
> Geoff Clare <netn...(a)gclare.org.uk>

I'm using KSH. Is there any way around this. It's really annoying. My
script works for say 10 machines but any greater connections it fails
while creating the file (using >> /tmp/out).
From: Mark Hobley on 11 Mar 2010 15:08
#! /shell/nerd <vikasera(a)gmail.com> wrote:
> I'm using KSH. Is there any way around this. It's really annoying. My
> script works for say 10 machines but any greater connections it fails
> while creating the file (using >> /tmp/out).

You need to secure a unique instance, before writing to the file:

http://markhobley.yi.org/shell/howto/nomulti.html

Mark.

--
Mark Hobley
Linux User: #370818 http://markhobley.yi.org/

From: Geoff Clare on 12 Mar 2010 08:40
Mark Hobley wrote:

> #! /shell/nerd <vikasera(a)gmail.com> wrote:
>> I'm using KSH. Is there any way around this. It's really annoying. My
>> script works for say 10 machines but any greater connections it fails
>> while creating the file (using >> /tmp/out).
>
> You need to secure a unique instance, before writing to the file:

That shouldn't be necessary with a POSIX-conforming shell.
The file should be opened with O_APPEND set, which will ensure
that no data is lost.

Some possible causes of the problem are:

1. The ksh that the OP is using doesn't set O_APPEND. Maybe clones
such as pdksh are like that; I doubt if any "real" ksh is.

2. The OP thinks the printf is being executed by ksh, but actually
it is being executed by a different shell.

3. The shell really is setting O_APPEND, and the underlying O/S has
a bug.

Before resorting to locking, the OP should at least try to find
out for sure whether O_APPEND is being set. On most systems he
should be able to do that using a tool such as truss or strace.

--
Geoff Clare <netnews(a)gclare.org.uk>

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