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Re: ifupdown writes to /etc... a bug?

This one time, at band camp, Goswin Brederlow wrote:
>Steve Langasek <vorlon@netexpress.net> writes:
>> On Sat, Mar 29, 2003 at 12:52:55AM +0100, Goswin Brederlow wrote:
>> > last call for complains about where to mount a writeable filesystem
>> > when a RO / is to be used. The mountpoint is only to appear when a RO
>> > / is actually used so all you RW / users are totally unafected.
>> > Opions so far have been (in order of my preference): (did I miss any
>> > sensible ones?)
>> > /etc/volatile
>> > /run
>> My preferences are reversed for the first two.  These files aren't
>> configuration at all, so the only justification for their inclusion under
>> /etc is "historical reasons".  It took me a while to even notice that tab
>> completion would be screwed up for /root, so I think tab completion is a
>> minor issue for this specific instance -- though it's one more reason why
>> all but the first two options are unsuitable.
>> Implementing /etc/volatile is a fairly innocuous change, and it would be
>> possible to move the contents to /run with a minimum of difficulty at a
>> later date if it becomes clear that the FHS would incorporate such a
>> change.  I still think it's best to put forth the additional effort to
>> get these files in /run straightaway, but I don't find /etc/volatile
>> completely inappropriate.
>So far its only checkroot.sh that has any notice of where the RW
>medium should be mounted. All other packages just follow the symlinks
>wherever they point.
>One could even just make the mountpoint a configure option at the top
>of the script or in /etc/volatile.conf or something.
>> If we were to move on /run, however, I think the appropriate course of
>> action would be to change all Debian packages to use /run as the
>> *authoritative* location for these files, and provide
>> backwards-compatible symlinks in /etc only for the benefit of admins and
>> local software.  The FHS specifically addresses the matter of where the
>> *system* looks for the software, so nothing else would be suitable for a
>> proposed amendment to the standard, IMHO.
>There is one thing that realy breaks everything so far and thats
>"/etc/nologin". Changing it affects several packages so it needs a
>standard place to be moved to.

Does any program create /etc/nologin automatically?

nologin(1) suggests that it is only checked for existence.

We are not trying to create a permanent ro /etc, we are merely aiming for
the much simpler goal of consitency in the FHS, and that means that program
state is not written to /etc, and instead written to /var/run or /run,
whichever is more available at the time.

>I see three options:
>A. /etc/volatile.conf says where volatile data can be found, look
>there for a "nologin" file.
>B. symlink /etc/nologin on RO /. Patch software to check if
>/etc/nologin is a symlink and then check if it is dangling as check
>for nologin.
>C. move /etc/nologin and patch software to look at the new place.

Thus all these are unneccessary.

I think you have a different goal in mind, and one that isn't a particularly
useful goal for Debian by default to provide.  Certainly we should allow the
admin of a machine to mount their /etc ro if they so desire, and that means
making sure *programs* do not attempt to write to /etc.

I am concerned that people aren't clear on the point of this thread, that
they are overengineering a solution to a problem that doesn't really exist.

jaq@debian.org                               http://people.debian.org/~jaq

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