📖 ~1 min read
Table of contents
Symptom & Impact
apt update returns 404 for repository paths and skips package index updates.
Environment & Reproduction
Typical after release transitions, typoed source entries, or mirror retirement.
Root Cause Analysis
Configured repository URL or suite component no longer maps to valid paths.
Quick Triage
Verify active release codename and compare source lines with official mirror paths.
Step-by-Step Diagnosis
Validate each configured source endpoint and component against current mirror layout.
Solution – Primary Fix
Correct sources list entries to supported Debian 12 repositories and refresh indexes.
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Solution – Alternative Approaches
Switch to a known-good mirror or local repository cache during outages.
Verification & Acceptance Criteria
No repository 404 messages appear and all index files download successfully.
Rollback Plan
Restore previous source list backup if replacement mirrors are unstable.
Prevention & Hardening
Automate source-list validation and codename checks during maintenance.
Related Errors & Cross-Refs
May overlap with NO_PUBKEY and release-file validity failures.
Related tutorial: View the step-by-step tutorial for Debian 9.
View all Debian 9 tutorials on the Tutorials Hub →
Browse all common problems & solutions on the Tutorials Hub.
References & Further Reading
Debian mirror policy and repository layout documentation.
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