As discussed previously, we want to have zstd support in 18.04 to evaluate and potentially enable it in later releases. We also want to add hooks for
snap integration to apt, this release is supposed to add them too.
The new features are not invasive - they are new code with a few places too hook them in. If no zstd is used, or if no hooks are registered, then there will be basically no change in behavior (or code paths).
# FEATURE: zstd
The zstd support adds a dependency on libzstd1 to libapt-pkg5.0. This should not have any effect on live images, since libzstd1 is part of the various live tasks, as btrfs-progs need it. For installed systems, this might be a new dependency (if they do not use btrfs, tor, or some other tools), so an increase of ~520 KB, as that's the size of the library and the library only depends on libc6.
This also depends on the zstd patch in dpkg being uploaded. If this unexpectedly does not happen, and I upload apt first, I'd revert it later before the release.
# FEATURE: hooks
The concrete code is still undergoing review, some option names might change for the hooks before release (e.g. pre-download might become pre-install-prompt, and the AptCli::Hooks config section only gets Install and Search lists for hooks to register, rather than individual pre-, post-, and fail- lists).
# other changes
We disable the seccomp sandbox for methods for the release, as it turns out there are still too many failure cases for it to be worthwhile to enable (NSS modules, weird libc functions calling weird syscalls, etc). People can re-enable it with a config option.
the rest is bug fixes. some change translatable strings in documentation, but fix up the translation too. A few additional strings are added to the sources.list man page ("mention mirror method in sources.list (Closes: 679580)", but I'm happy to back them out.
There are also some CI fixes, and the major cache version is bumped so we can issue updates independently for 1.5 and 1.6 apt release series.
Diff for 1.6~rc1 from ~beta1