Debian 12 – apt install fails with unmet dependency chain – Fix & Prevention

📖 ~1 min read

Table of contents

1. Symptom & Impact
2. Environment & Reproduction
3. Root Cause Analysis
4. Quick Triage
5. Step-by-Step Diagnosis
6. Solution – Primary Fix
7. Solution – Alternative Approaches
8. Verification & Acceptance Criteria
9. Rollback Plan
10. Prevention & Hardening
11. Related Errors & Cross-Refs
12. References & Further Reading

Symptom & Impact

Applications cannot be installed because package constraints conflict across repositories.

Environment & Reproduction

Often appears after mixing stable with testing/unstable repos or stale apt pin files.

Root Cause Analysis

APT solver cannot satisfy version requirements due to pinned priorities and held packages.

Quick Triage

Inspect apt policy and package holds before forcing any transaction.

Step-by-Step Diagnosis

Run: apt-cache policy ; apt-mark showhold; grep -R . /etc/apt/preferences /etc/apt/preferences.d 2>/dev/null; sudo apt -o Debug::pkgProblemResolver=yes install .

Solution – Primary Fix

Run: sudo apt-mark unhold ; remove conflicting pin entries; sudo apt –fix-broken install; sudo apt install -y.

Solution – Alternative Approaches

Use curated internal mirrors and explicit target release pinning to avoid cross-suite drift.

Verification & Acceptance Criteria

APT resolves package graph without broken dependency or held package messages.

Rollback Plan

Reinstate prior pin set and previous package versions if runtime compatibility regresses.

Prevention & Hardening

Govern repository policy centrally and lint pin files in CI before rollout.

Related Errors & Cross-Refs

Related to held packages, partial upgrades, and missing package candidate incidents.

Related tutorial: View the step-by-step tutorial for debian-12.

View all debian-12 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

APT preferences manual and Debian package dependency resolution documentation.