Debian systems and assumptions about user rights (was: Braindump: Can we get rid of the font-cache-group question?)

[Frank Küster <frank@debian.org>]

Okay, let's take this to -devel; I hope we'll get a bit more of answers
instead of just new questions there...

We are thinking about ways to make TeX font caching safer than it
currently is, without breaking buildd's or unusual setups.  The current
idea is to cache the font data in each user's home directory, and only
if this does not exist or is not writeable, fall back to VARTEXFONTS;
but this variable would no longer point to /var(/cache/fonts), but to
/tmp/texfonts instead.

Florent Rougon <f.rougon@free.fr> wrote:

> BTW, about the /tmp/texfonts directory, won't it be a problem if one
> user creates it (not manually, but as suggested in this thread, by way
> of mktexnam or whatever kpathsea program) and then, *another user* also
> needs it to store fonts? Under normal circumnstances, the second user
> won't have the permissions to write to /tmp/texfonts.
>
> I didn't follow the discussion very closely, so I may say something
> wrong here. If I understood correctly, /tmp/texfonts would be only used
> for a user who has no $HOME and thus cannot write the font data to
> TEXMFVAR. If this is right, the previous paragraph could only happen
> with such users (buildds?), but still, it may happen...

I think we should not rely on current implementations here, but instead
consider which setups should generally be supported, and which need
not.  Therefore I'd like to hear comments from -devel about the
following questions:

- Setups without an existing $HOME directory can exist, and package
  building must work there, correct?

  (one easy way to set this up is copy /etc/passwd to /chroot/etc/passwd
  and su to a user.  Or some users of su/sudo with "pbuilder login"
  which do not unset $HOME)

- /tmp/ will always be available to create a reasonable amount of data?

- If package builds or other automated tasks happen on a system and are
  performed by a local user who has no home directory, can we assume
  that it will always be the same user, and use a system-wide unique
  name for the font cache directory withing /tmp?  

  I fear the current implementation of the font generating scripts does
  not allow to create font cache directories in /tmp which have the
  username in their paths (although with some hazzle it might be
  doable).

This current discussion has started at 
http://thread.gmane.org/gmane.linux.debian.devel.tetex/16065/focus=16065

but the problem is old and has been thought about over and over again in
a multitude of threads, even here on -devel...

TIA, Frank
-- 
Frank Küster
Single Molecule Spectroscopy, Protein Folding @ Inst. f. Biochemie, Univ. Zürich
Debian Developer (teTeX)