incompatible screen update

[Lennart Poettering]

On Tue, 08.02.11 12:09, Miroslav Lichvar (mlichvar at redhat.com) wrote:

> 
> On Tue, Feb 08, 2011 at 08:42:52AM +0100, Lennart Poettering wrote:
> > On Fri, 04.02.11 16:30, Miroslav Lichvar (mlichvar at redhat.com) wrote:
> > > - $HOME/.screen is used as socket directory instead of
> > >   /var/run/screen
> > 
> > $HOME is no place to place unix sockets. Unfortunately $HOME might be
> > one weirdo file systems which do not support that. Expect bug reports
> > about this soon.
> 
> Hm, screen wouldn't be the only one doing that, I see in my home
> sockets belonging to rxvt-unicode and uim. Anyway, the directory can
> be set by SCREENDIR environment variable.
> 
> Is this worse than allowing users to write in /var/run/screen? (bug #667252)

Good question.

Precisely for issues like this XDG_RUNTIME_DIR has recently been
introduced:

http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html

We carefully made sure to define the semantics of this dir to offer a
safe place to put these sockets.

While it might appear easy to simply make use of XDG_RUNTIME_DIR if set
in screen, and have all problems go away on modern systems (i.e. >= F15),
but unfortunately things aren't that easy: the lifetime of
XDG_RUNTIME_DIR is strictly bound to the user being logged in. Since
screen currently does not set up a PAM session it does not count as
login right now and hence will not be able to use this dir when the user
terminates all his real logins.

That all said, I actually do believe that screen should invoke the PAM
session setup code. Ideally, one of those days we enable automatic
cleanup of all processes started from a session when a session
ends. That would break screen unless it is fixed to set up its own
session environment. So, sooner or later it would be really great to
have screen fixed this way.

Lennart

-- 
Lennart Poettering - Red Hat, Inc.