From: Mike Hall <mghall@...>
Date: 2003-07-27T00:45:57+09:00
Subject: Re: Confused about locking a file via file.flock(File::LOCK_EX)

Mark J. Reed  wrote:

>There is no *mandatory* file locking mechanism on UNIX.
>It's always possible to just ignore any locks and open a file
>for writing.

I have to disagree.  SVR2 had it way back when,
and Linux used to, last time I checked a few years ago.
As I recall, I could put a mandatory lock on a file, and even 'cat' would object.

    * Mandatory locking
          o kernel enforces lock requests
          o access to records is controlled by the kernel
          o open, close, read, write system calls honor the locks
          o requires SGID bit set, with group-execute bit cleared
                + chmod u+rw,g+rws-x,o+rw file
          o in Linux, requires a MAND_LOCK mounted filesystem
                + mount -o remount,mand /filesystem
                + mount -o remount,nomand /filesystem
          o a write-lock prevents _any_ process from reading that section


I have no idea what AIX supports in this regard.