[Pkg-zsh-devel] Bug#1023317: Bug#1023318 / Bug#1023317: {screen, zsh}: re-adds /usr/bin/{screen, zsh} to /etc/shells on upgrade

[Axel Beckert]

Hi Helmut,

thanks for these bug reports and making us aware of this type of
issue.

Some more hints about how this all is meant to work and why it
actually works would have been appreciated, though:

Helmut Grohne wrote:
> When upgrading or reinstalling screen, it adds /usr/bin/screen to
> /etc/shells even if one locally removed it there. Such behaviour
> violates Debian policy section 10.7.3. I propose managing the entry
> declaratively using dpkg triggers and am attaching a patch for your
> convenience.
> +	install -D -m644 debian/shells $(ROOT)/usr/share/debianutils/shells.d/screen
[…]
> -  add-shell /usr/bin/screen || true
[…]
> -if [ "$1" = disappear ]; then
> -  remove-shell /usr/bin/screen || true
> -fi

It took me quite a while to where this
/usr/share/debianutils/shells.d/ comes from and where it is this
documented,

/usr/share/doc/debianutils/README.shells.gz clearly states that I
should use add-shell and remove-shell:

| So, if a package contains something that the maintainer thinks ought
| to be a valid login shell, it's postinst should, (on initial install
| only, to allow a sysadmin to take it out again), run:
|
| /usr/sbin/add-shell /path/to/shell
|
| In the postrm, probably on remove, the package should call
| 
| /usr/sbin/remove-shell /path/to/shell
| 
| As the various shells start to use it, the default shells list will
| shrink.

No mention of that directory. The man pages add-shell(8) and
remove-shell(8) don't mention this directory either.

Also can't find it mentioned in
/usr/share/doc/debianutils/changelog.Debian.gz.

I also found no mentioning of triggers inside the functional part of
the patches. So I assume you meant to refer to
/var/lib/dpkg/info/debianutils.triggers (which also seems not to be
mentioned in /usr/share/doc/debianutils/changelog.Debian.gz).

Finally when looking /var/lib/dpkg/info/debianutils.postinst, I found
a pointer to update-shells whose man-page explains that whole
mechanism and also why it actually track changes made by the
administrator. An early pointer to that or #990440 would have been
nice…

		Regards, Axel
-- 
 ,''`.  |  Axel Beckert <abe at debian.org>, https://people.debian.org/~abe/
: :' :  |  Debian Developer, ftp.ch.debian.org Admin
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