#134758 dpkg-query: Make -S handle unowned symlinks resolving to owned pathnames

Package:
dpkg
Source:
dpkg
Description:
Debian package management system
Submitter:
Richard Kettlewell
Date:
2021-11-12 04:00:03 UTC
Severity:
wishlist
#134758#5
Date:
2002-02-19 22:23:20 UTC
From:
To:
dpkg -S only compares filenames lexically: so symlinks can lead to
annoying false negatives, as in the following example:

    lyonesse$ type xterm
    xterm is /usr/bin/X11/xterm
    lyonesse$ dpkg -S /usr/bin/X11/xterm
    dpkg: /usr/bin/X11/xterm not found.
    lyonesse$ realpath /usr/bin/X11/xterm
    /usr/X11R6/bin/xterm
    lyonesse$ dpkg -S /usr/X11R6/bin/xterm
    xterm: /usr/X11R6/bin/xterm

However, realpathing the search term doesn't solve the problem:
consider the case where the operator has replaced some standard
directory such as /usr/sbin with a symlink (e.g. to split up /usr over
several partitions due to space constraints, or to identify /usr/sbin
with /usr/bin).  Then realpathing the search term would result in
*nothing* in /usr/sbin matching, which is even worse than the current
behaviour.

realpathing filenames as they are written to PACKAGE.list at
install time would solve this, but would break the ability of the
operator to move bits of filesystem around leaving links behind to
keep the standard names working without telling dpkg about it, which
is surely an unreasonable imposition.

realpathing them as they are read from PACKAGE.list in the process of
implementing -S would work better, but dpkg -S is far too slow
already.  Even with caching, this would amount to 100,000 or more
lstat() calls on a reasonably package-heavy system.

Anyone got any better ideas?

A solution to the exact example quoted above would be to insist that
PATH entries be the same as the path found in debfiles, (so
e.g. /etc/profile would have /usr/X11R6/bin where it now has
/usr/bin/X11).  However this is not a general solution.

ttfn/rjk
#134758#10
Date:
2005-04-29 10:54:53 UTC
From:
To:
Hi,

I do not know much about realpath, I have never used it previously.
I assume that using which instead of realpath would not solve the
speed problem, would it?

Regards

Rolf
#134758#25
Date:
2016-12-12 12:53:25 UTC
From:
To:
Hi,

Now that some users enabled "usrmerge" it has become more important
that "dpkg -S" deals sensibly with symlinks. I have thus raised the
severity of this bug to important (following the discussion
with Helmut in #843073).

Cheers,