redis: package takes over /etc/redis/redis.conf without Conflicts/Replaces — a single file clash fails the whole apt transaction

[planitron]

Summary

The Pigsty redis package installs /etc/redis/redis.conf, a file owned by redis-server, but declares neither Conflicts: nor Replaces: for it. When both are present on a node, dpkg refuses the unpack:

trying to overwrite '/etc/redis/redis.conf', which is also in package redis-server 6:7.2.7-1rl1~noble1

Because dpkg aborts the whole run, this is not limited to redis. On one upgrade, a single clashing package left 24 packages unpacked-but-not-configured — including a kernel. A machine in that state that reboots comes up on a half-installed system, which is a far worse outcome than the package conflict itself.

Root cause

Debian Policy §7.6 ("Overwriting files in other packages") requires a package that takes over files from another to declare Replaces:, and Conflicts: when the two cannot be co-installed.

The Pigsty package is monolithic (server + CLI in one deb) while the distribution splits them, so the two packaging layouts cannot coexist — which is fine, but it has to be declared:

$ apt-cache show redis | grep -E '^(Package|Version|Depends|Conflicts|Replaces|Provides):'
Package: redis
Version: 6:7.2.15-4PIGSTY~noble
Depends: adduser, libc6 (>= 2.38), libssl3t64 (>= 3.0.0), libsystemd0

No Conflicts:, no Replaces:, no Provides:. For comparison, the distribution package is a metapackage:

Package: redis
Version: 5:7.0.15-1ubuntu0.24.04.4
Depends: redis-server (<< …), redis-server (>= …)

Note this is not specific to one repo snapshot: apt-cache madison redis shows the Pigsty repo currently serves only 6:7.2.15-4PIGSTY~noble, so a v4.5.0 install gets the same package.

Reproduction

On a Debian/Ubuntu node:

1. install redis-server from the distribution or from the redis.io repo (this also happens when it was pulled in earlier by an unrelated role or by an operator);
2. run any apt-get upgrade that brings in the Pigsty redis package.

The transaction fails at the unpack stage, and every other package in the same run is left unconfigured.

Environment

Pigsty	v4.4.0, and the same package is served for v4.5.0
OS	Ubuntu 24.04 LTS
Pigsty package	redis 6:7.2.15-4PIGSTY~noble
Clashing package	redis-server 6:7.2.7-1rl1~noble1 (redis.io) — the distribution redis-server owns the same path

Suggested fix

Declare the relationships in the redis package metadata:

Conflicts: redis-server, redis-tools
Replaces: redis-server, redis-tools
Provides: redis-server, redis-tools

Provides: also lets packages that depend on redis-server remain satisfiable, which the current monolithic package breaks.

With those fields, dpkg replaces the distribution packages cleanly instead of aborting, and an unrelated package upgrade can no longer be taken down by a redis file clash.

Wider note (not part of this report)

Other Pigsty-built packages that shadow distribution ones (haproxy, etcd, grafana, vector) also declare no Conflicts/Replaces. I have not verified whether their file sets actually overlap with the distribution equivalents, so I am not claiming they are affected — only that it may be worth a look while touching the packaging pipeline.