Re: unshare -m and mount propagation

[yumkam@gmail.com (Yuriy M. Kaminskiy)]

Karel Zak <kzak@redhat.com> writes:

> On Fri, Mar 18, 2016 at 05:26:25AM +0300, Yuriy M. Kaminskiy wrote:
>> I think this issue should be at least documented. And, maybe, default
>> `--propagation` should be changed to `slave`.
>
> The reason why we use 'private' is that it's the kernel default for
> years and it's what has been expected by users for long time before we
> introduced --propagation and any unshare(1) default.
>
> The current --propagation default unifies things and makes unshare(1) 
> portable to distributions where root fs is mounted as 'shared' (e.g. 
> systemd distros) and all this in backwardly compatible way for users
> who have no clue about --propagation.
>
> So, I don't think we want to change any default to corrupt scripts where
> is no explicitly specified --propagation. 

By you already broke scripts that expected old a-la '--propagation
unchanged' behavior.
E.g. one my script did
   unshare -m sh -c 'mount --make-rslave /; ...'
Now I must check for util-linux version and either use --propagation
option, or mount --make-rslave (you cannot revert back from private to
slave).
(And as I said, 'private' breaks umount propagation and thus very bad for
long-running namespaces).