From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org (Eric W. Biederman) Subject: Re: Virtualizing /proc/sys/kernel/random/boot_id per container ? Date: Thu, 30 Aug 2012 17:18:06 -0700 Message-ID: <874nnjhq2p.fsf@xmission.com> References: <20120830211832.GA3297@redhat.com> <878vcwjabu.fsf@xmission.com> <20120830232239.GE9226@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20120830232239.GE9226-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> (Daniel P. Berrange's message of "Thu, 30 Aug 2012 16:22:39 -0700") List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: "Daniel P. Berrange" Cc: containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org List-Id: containers.vger.kernel.org "Daniel P. Berrange" writes: > On Thu, Aug 30, 2012 at 03:15:17PM -0700, Eric W. Biederman wrote: >> "Daniel P. Berrange" writes: >> >> > One of the features that SystemD folks have asked us to fix in LXC, is >> > to make sure that /proc/sys/kernel/random/boot_id changes each time a >> > container is started. >> >> There may be a good reason for this. Most of the time what I have seen >> of kernel requests from the direction of SystemD is that while there may >> be a real problem but usually their imagined solution is not a >> particularly good solution. So a description of the problem is needed. >> >> Justifying something with just SystemD wants this is a good way to get >> a nack. >> >> > The current semantics are that this file produces a new random UUID each >> > time the host OS is booted. Obviously each time we start a container now, >> > they just see the host's random boot_id, so from a container's POV this >> > does not change each time it starts. >> >> That is correct. As I recall the contract with boot_id is to provide >> a unique per boot value to assist in dealing with boots etc. I seem >> to recall emacs uses the combination of hostname+boot_id to help >> generate unique lock files names. >> >> I would definitely need a refresher on how boot_id is used in practice >> by applications other than SystemD before I could suggest a good design. > > This post seems to describe what emacs wants boot_id for: > > http://marc.info/?l=linux-kernel&m=93613053109494&w=2 > > With this info, I think emacs inside a container would expect the boot_id > to change each time the container is started, so they can detect stale > locks from an emacs instance in a previous boot of the container. Thanks that patch does clarify the original purpose. Unfortunately the lines of communication were crossed because emacs 24.1 most certainly does not use /proc/sys/kernel/random/boot_id. Eric