Public bug reported:
Summary generated by Gemini 3.8 Flash
Package: apt, libapt-pkg7.0
Severity: critical
Tags: upgrade-failure, packaging
[Summary]
During a release upgrade to Ubuntu 26.04 (resolute), if dpkg encounters any
error (such as an unowned file in xkb-data or disk
space issue) after unpacking libapt-pkg7.0 but before unpacking the apt
binary, the package manager becomes completely non-
functional with a symbol lookup error. This leaves the system in a broken,
half-upgraded state that cannot self-heal or be
repaired via 'apt' / 'apt-get'.
[Root Cause]
Between apt 3.1.6ubuntu2 and apt/libapt-pkg7.0 3.2.0, the C++ ABI changed:
- In 3.1.6:
APT::Solver::InternalCliWhy(pkgDepCache&, pkgCache::PkgIterator, bool)
Mangled:
_ZN3APT6Solver14InternalCliWhyB5cxx11ER11pkgDepCacheN8pkgCache11PkgIteratorEb
- In 3.2.0:
The function was moved into the DependencySolver class:
APT::Solver::DependencySolver::InternalCliWhy(pkgDepCache&,
pkgCache::PkgIterator, bool)
Mangled:
_ZN3APT6Solver16DependencySolver14InternalCliWhyB5cxx11ER11pkgDepCacheN8pkgCache11PkgIteratorEb
Flaws in packaging:
1. Both 3.1.6 and 3.2.0 use the same symbol version tag: APTPKG_7.0.
2. Both share the same package name: libapt-pkg7.0.
3. Crucially, the package libapt-pkg7.0 (3.2.0) DOES NOT declare:
Breaks: apt (<< 3.2.0)
Because libapt-pkg7.0 (>= 3.1.6) is satisfied by 3.2.0, dpkg is permitted
to unpack libapt-pkg7.0 ahead of the apt binary. If
an error occurs in any intermediate package, the system is left with:
- /usr/lib/x86_64-linux-gnu/libapt-pkg.so.7.0 (version 3.2.0)
- /usr/bin/apt (version 3.1.6)
Any invocation of 'apt' or 'apt-get' immediately crashes with:
"apt: symbol lookup error: apt: undefined symbol:
_ZN3APT6Solver14InternalCliWhyB5cxx11ER11pkgDepCacheN8pkgCache11PkgIteratorEb,
version APTPKG_7.0"
When do-release-upgrade catches the dpkg error, it invokes apt/python3-apt
to analyze or explain why packages failed, which
triggers this crash and completely aborts the recovery mechanism.
[Real-World Trigger Example]
In this instance, the upgrade was interrupted by xkb-data (2.46-2):
- The user had a custom layout file created in
/usr/share/X11/xkb/symbols/grouplock/mycapslock.
- During unpack, dpkg-maintscript-helper dir_to_symlink failed:
"dpkg-maintscript-helper: error: directory '/usr/share/X11/xkb' contains
files not owned by package xkb-data:all, cannot
switch to symlink"
- dpkg exited with code 1 at package #27 (xkb-data).
- libapt-pkg7.0 was already unpacked at 3.2.0, but apt was still 3.1.6.
- The system became unrecoverable without manual low-level dpkg
intervention.
[Steps to Reproduce]
1. Install an earlier Ubuntu release (e.g. 24.04 / 25.10).
2. Place any unowned file in a directory slated for dir_to_symlink:
sudo touch /usr/share/X11/xkb/symbols/custom_test_file
3. Run do-release-upgrade to 26.04.
4. dpkg will abort upon processing xkb-data.
5. Attempt to run 'apt' or 'apt --fix-broken install'.
6. Observe:
apt: symbol lookup error: apt: undefined symbol:
_ZN3APT6Solver14InternalCliWhyB5cxx11ER11pkgDepCacheN8pkgCache11PkgIteratorEb,
version APTPKG_7.0
[Proposed Fix]
In the 'apt' source package (debian/control), add the appropriate Breaks
relation:
Package: libapt-pkg7.0
Breaks: apt (<< 3.2.0)
This forces dpkg to unpack 'apt' and 'libapt-pkg7.0' synchronously,
preventing the ABI mismatch window during release upgrades
ProblemType: Bug
DistroRelease: Ubuntu 26.04
Package: apt 3.2.0
ProcVersionSignature: Ubuntu 6.17.0-41.41-generic 6.17.13
Uname: Linux 6.17.0-41-generic x86_64
ApportVersion: 2.34.1-0ubuntu0.1
Architecture: amd64
CasperMD5CheckResult: unknown
CurrentDesktop: ubuntu:GNOME
Date: Sun Sep 6 10:34:40 2026
RebootRequiredPkgs: Error: path contained symlinks.
SourcePackage: apt
UpgradeStatus: Upgraded to resolute on 2026-09-05 (1 days ago)
** Affects: apt (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug resolute wayland-session
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https://bugs.launchpad.net/bugs/2166595
Title:
libapt-pkg7.0 3.2.0 causes apt symbol lookup error (missing Breaks:
apt << 3.2.0) on do-release-upgrade
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