User Questions

Q: What can be done when the dpkg lock is held?

A: This means another instance of dpkg or a frontend is running, so the correct solutions are to: let the other process end its execution, find the frontend and quit it, or kill any such frozen processes.

Removing the dpkg lock is not a correct solution, as dpkg uses region locking on an existing file. The presence of the file does not mean that the lock is currently being held, and removing it can most probably cause dpkg database corruption.

Q: Why does ''dpkg --set-selections'' not record selections for unknown packages?

A: Due to multiarch, the dpkg command-line interface dealing with package name input needed to change. To avoid the possibility for dpkg to be unable to refer to packages in its own database, selections for unknown packages are not recorded any longer. So the available database needs to be up-to-date before any selection is set, this also gives the benefit of warning on unknown packages so that the user knows what will be missing. There are several ways to update the available database, depending on the package manager frontend being used, any single one of them will be enough:

Behavior Questions

A: No. As dpkg does not currently track file metadata, it does not know if a symlink or directory was switched by a previous package or by the sysadmin. As part of the dpkg credo, preserving human configuration is of upmost importance, and this kind of change has always been considered as so.

As of now, this should be handled by the package maintainer scripts, failing to do so should be considered a serious bug.

Q: Can dpkg be told to avoid invoking a harmful prerm from an installed package on upgrade?

A: No. There's currently no way to tell dpkg not to execute such prerm maintainer scripts, but there is an extreme workaround available.

Only if the prerm is doing something really harmful, not just for simple failures or actions that can be easily reverted by the new postinst, then the only available way is to make a new, independant package that replaces the broken package's prerm, and then make the new version of the broken package pre-depend on it. This requires modifying the dpkg database, and as such is strongly discouraged, and should only be used as a last resort measure. Proposed by Joey Hess.

Q: Can dpkg handle volatile files?

A: Partially. dpkg does not have full native support (yet) for volatile files (those that might change during the life of a specific installed version), but there are some workarounds that can be used for now:

  1. Ship an initial file (possibly empty) on the .deb that gets modified on the filesystem later on, but this will make the file hashes not match with stuff like debsums or the upcoming «dpkg --verify». While this might be the most convenient option, it's also possibly the most wrong one. This should never be used for volatile files such as logs or caches or the like.

  2. Do not ship the file in the .deb, and generate it at installation time, run-time or whenever, but the maintainer scripts will need to deal with the removal manually. This is the more correct but slightly more cumbersome option.
  3. If the volatile file changes are due to external forces, like updates from a website or similar, then it might be best to automatically generate a new package every time these files change, and ship them normally in a package from a repository.

In the future, dpkg might acquire the ability to register external files, and one kind of such files could be changing files, so dpkg would take care of removing them, and would not store file hashes for these, etc.

Feature Request Questions

Q: Can we add support for new compressors for .dsc packages?

A: Adding more compression formats support to dpkg-source, has some benefits as it avoids having to repack the original source tarball, and in this way checksums or upstream signatures are preserved, it might also improve compression ratio compared to previous supported compressions.

But then the costs of adding support for an additional compression format are quite high, to the point that those benefits seem small compared to them. The costs are (at least): increase in the build-essential set; the new compression becomes part of the source format forever, as it can never be taken back as old Debian packages or 3rd-party packages in the wild might be using that format; it's another (uncommon) package required on non-Debian-based systems to be able to handle those source packages.

With the above in mind, the new compression format should really be very widely used to distribute upstream source and it should improve compression ratio compared to previously supported formats to start considering adding it.

Q: Can we add support for new default build flags to dpkg-buildflags?

A: Certainly. But before considering adding any flag to the default, the following things would need to be done: