I'm not sure whether this is me being stupid, or a real issue.
On my CentOS 6 system the manpage for flock()2 states that it does not
work on NFS. When I check for the latest version online, it is the same.
Experimentally, the flock shell command does work on an NFS3 mounted
volume in (at least) CentOS 5 with 2.6.18.
In http://nfs.sourceforge.net/ I find
"The NFS client in 2.6.12 provides support for flock()/BSD locks on NFS
files by emulating the BSD-style locks in terms of POSIX byte range
locks."
In fs/nfs/file.c I find "We're simulating flock() locks using posix locks
on the server"
That seems to imply to me that flock() does in fact work on Linux since
2.6.12, at least as far as a programmer is concerned.
http://man7.org/linux/man-pages/man2/flock.2.html
NOTES
flock() does not lock files over NFS. Use fcntl(2) instead: that
does work over NFS, given a sufficiently recent version of Linux and
a server which supports locking.
--
Andrew Daviel, TRIUMF, Canada
Tel. +1 (604) 222-7376 (Pacific Time)
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