On 10/09/2015 12:11, tilt! wrote:
>
> Since i already use $HOME/.config for configuration data,
> which more precisely is the default setting of XDG_CONFIG_HOME
> (according to [1]), i would like to consider the pendant
> XDG_RUNTIME_DIR for the tempfile i have described.
>
> Unfortunately, the specification [1] does not provide a default
> for XDG_RUNTIME_DIR as it does for XDG_CONFIG_HOME.
>
> In Ubuntu, there used to be libpam-xdg-support (see [2]). It
> sets up a directory in "/run/user", if neccessary, at login
> time of the user. More recently, this task has been assumed by
> pam-systemd (see [3]).
>
> Question open for debate:
>
> On a systemd-free system, should an alternative exist which
> assumes the task of initializing XDG envvars as described by
> [1] in the way done by [3]?

This part of the XDG specification is pretty terrible. It's poorly
specified, and the behaviour as specified is only implementable by
systemd (i.e. its lifetime by refcounting all the logins/logouts). It
also precludes having more than one session per user. By design... It
wouldn't have required much effort to make this more flexible, but the
authors of this "specification" don't generally bother with
forward-looking flexible design.

There's no technical reason for /run/$user to live under /run. It could
be just as easily live under /tmp (or /var/tmp). So you could default
it to use /tmp/$user or /tmp/xdg-runtime/$user or whatever and make this
the default.

[I argued for doing this originally, since /run/user would allow one to
easily harm the system or other users by filling /run and/or /run/user
depending on how the mounts are set up which would prevent other user's
sessions and system services working properly, but I was told this was
not a problem. And also, that /tmp could not be used because of
tmpreaper. However, it's in reality another case of RedHat-specific
constraints and workarounds being used to dictate policy. They have
tmpreaper running by default, and don't have it set to ignore certain
directories. In their world, this means using /tmp is an unreliable
nightmare. However, using /tmp is entirely possible, and it's also
possible even when tmpreaper is installed if it is configured
appropriately (they considered this impossible...). Obviously
configuring an optional service is preferable to a poorly-configured
default influencing your system design, but very little these people do
makes much objective sense.]

So my recommendation here would be to
- place /run/user in a subdirectory of /tmp
- configure XDG_RUNTIME_DIR to use this location either in a PAM module,
or even by hardcoding the default to use this location--the
specification might not provide this default, but an implementation
certainly can.


Regards,
Roger