[rb-general] Remaining reprotest variations

[Ceridwen]

For most of the variations I've done so far, I've been either
depending on external utilities or had POSIX-compliant ways to execute
them.  The rest of the variations pose more problems.

1. user_group.  The POSIX standard includes the notion of user/group
ids, but the only ways it defines to change the uid/gid of processes
are C functions.  Unfortunately, there's also nothing in the POSIX
standard for creating users, though at least `chown` is.  At the
moment, my plan is to use `useradd`, `groupadd`, `userdel`,
`groupdel`, and `su`.  (Using 'sudo' like prebuilder does is more
complicated and less likely to be supported everywhere.)  I'm going to
set the ids to something like 20000.  This page,
http://bhami.com/rosetta.html, indicates that this won't work on
FreeBSD or MacOS X, and thatis supported by these pages,
http://www.math.utah.edu/~beebe/unix/g/groupadd.html and
http://www.math.utah.edu/~beebe/unix/u/useradd.html.
    - What works on FreeBSD/MacOS X?
    - Are there any other problems I'm likely to encounter using `su`?

2. host and domain.  Host name is only only mentioned in the POSIX
standard in the context of uname and some C functions for getting
information about it, and domain name isn't mentioned at all in the
standard, AFAICT.  However, according to
http://www.math.utah.edu/~beebe/unix/h/hostname.html and
http://www.math.utah.edu/~beebe/unix/d/domainname.html, `hostname` is
universal enough, and since Linux now has `domainname`, it is too.
The prebuilder script also modifies `/etc/hosts`.
    - Is modifying /etc/hosts necessary in general?
    - If so, is it portable?
    - If not, what modifications are necessary on other distros and
OSes?

3. bin_sh.  prebuilder uses dpkg-reconfigure here, which doesn't work
for reprotest.
    - Is it safe to assume that /bin/sh is a symlink?
    - What shells should be available on most POSIX systems?
    - Does this variation need to search for available shells?
    - If so, Is there a portable way to determine what shells are
available?

4. user_shell: prebuilder uses `usermod`, but there's also `chsh`.
`chsh` looks a little more common:
http://www.math.utah.edu/~beebe/unix/c/chsh.html
vs. http://www.math.utah.edu/~beebe/unix/u/usermod.html.  I also don't
know if all versions of `usermod` support the -s option.
    - Will `chsh` work here?
    - If not, has `usermod`'s portability improved?

5. kernel: While `uname` is in the POSIX standard, mechanisms for
altering its output aren't.  `setarch`, what prebuilder uses and what
reprotest uses at the moment, is Linux-specific.
    - What methods of changing `uname` will work on other OSes?

5. locales: Is there a portable way to figure out what locales are
available?

6. time: tests.reproducible-builds.org sets the system clock into the
future for some machines, which doesn't work here.  I can try to use
libfaketime for non-qemu environments and make the VM clock
independent for qemu, but this is likely to get very tricky.  How much
time should I spend on this?

Beyond the specific variations, I have some questions about reversion
that apply to several variations.  I'm trying to have reprotest revert
all the changes it makes on its own, to make it more useful for
simpler execution environments, but guaranteeing this under all
conditions is tricky.

* If reprotest is called as root without any virtualization
  (i.e. null), should it attempt to run the variations that require
  root privileges on the host system?  These are host, domain, bin_sh,
  and user_group.  I'm reluctant to disable this functionality
  altogether, because I can see someone wanting it, but it definitely
  has the potential to cause undesirable side effects if something
  goes wrong.

* Along the same line, `chsh` affects all user shells.  This doesn't
  require root privileges, but should it be tested without
  virtualization?

* Are there any other variations which shouldn't be tested in some of
  the execution environments without full reversion capabilities?

Ceridwen