Unable to lock a file to stop sendmail writing to it

Ben Morrow · *nix forums Guru Wannabe Joined: 24 Apr 2006 Posts: 193

Quoth "GarfGarf" <garfield_99999@yahoo.com>:

GarfGarf · *nix forums beginner Joined: 16 Nov 2005 Posts: 4

Gunnar Hjalmarsson wrote:

Gunnar Hjalmarsson · *nix forums Guru Joined: 26 Feb 2005 Posts: 852

GarfGarf wrote:

anno4000@radom.zrz.tu-ber · *nix forums beginner Joined: 05 Jul 2006 Posts: 40

GarfGarf <garfield_99999@yahoo.com> wrote in comp.lang.perl.misc:

GarfGarf · *nix forums beginner Joined: 16 Nov 2005 Posts: 4

Hi all,

I am trying to write a script that reads a mailbox that sendmail
updates, but I want to be able to lock the file, read the file, empty
the file and unlock the file again.
The problem I have is that locking doesn't seem to work. As I can't
lock the file, sendmail writes into the file while i'm writing and that
causes all sorts of problems.

Here are some things I tried:-

sysopen(FH,"/tmp/file",O_EXCL | O_RDWR) || die "Error:$!";
print "File opened\n";
sleep 20;
close FH;

or

use Fcntl ':flock'; # import LOCK_* constants
open(FILE,"</tmp/file") || die $!;
flock(FILE,LOCK_EX);
sleep 20;
close FILE;

each one of those should lock the file, and hold the lock for 20
seconds.
However during that 20 seconds I can still run date >> /tmp/file
and it gets written to.

This happens both on solaris and linux.

Help !

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