Complete procedures with a way back.

Sub-process /usr/bin/dpkg returned an error code (1) is a final summary, not the root cause. The decisive message normally appears earlier in the transaction. This guide preserves that first failure, checks package-manager ownership, locks, disk and filesystem health, audits dpkg state, then completes configuration or performs a targeted rollback without deleting lock files or forcing unrelated removals.

Verify the official installer checksum, install Composer in a controlled path, enforce lock files, audit dependencies, and deploy without development packages.