Bug#1121807: ITP: dpkg monthly named logs via symlink (replace logrotate dependency)

Package: dpkg
Version: 1.22.21
Severity: wishlist

Dear Maintainer,

## Problem

Current dpkg.log rotation via `/etc/logrotate.d/dpkg` (monthly, rotate 
12) has several limitations:

1. Limited history: Only 12 months retained by default
2. logrotate dependency: Cron overhead, configuration complexity
3. No distro-long tracking: Current logs don't contain Debian version info
4. Manual cleanup complexity: `rm dpkg.log.*` vs explicit `rm dpkg-2025-*`
5. Tooling expectations: Scripts expect `dpkg.log`/`dpkg.log.1` pattern

## Proposal: Symlink-based Monthly Logs

Keep dpkg-core UNCHANGED. Use `/var/log/dpkg.log` as symlink to current
monthly file.
Optionally prepend Debian version to log filenames:

dpkg-trixie-2025-12.log ← /var/log/dpkg.log (symlink, current month 
UNCOMPRESSED)
dpkg-trixie-2025-11.log.gz (COMPRESSED)
dpkg-trixie-2025-10.log.gz (COMPRESSED)
dpkg-trixie-2025-09.log.gz (COMPRESSED)
dpkg-bookworm-2025-08.log.gz (COMPRESSED)
...
dpkg-bookworm-2024-12.log.gz (COMPRESSED)
...

Benefits:
✅ NO dpkg core changes (fopen("/var/log/dpkg.log") works transparently)
✅ NO logrotate dependency (1 cron.monthly job)
✅ Distro-long history WITH version info: zgrep upgrade /var/log/dpkg-*.log
✅ Manual control: rm /var/log/dpkg-trixie-*.log
✅ Atomic switches via rename()
✅ ~15kB/month compressed → 500kB/3 years (negligible)
✅ Works on embedded (RPi, IoT) without rotation complexity

## Implementation (Trivial)

1. dpkg.cfg.d/10-symlinklogs:

LOGFILE="/var/log/dpkg.log"


2. /etc/cron.monthly/dpkg-monthly:

#!/bin/bash
# Atomic monthly log switch with optional distro prefix
DISTRO=$(grep '^VERSION_CODENAME=' /etc/os-release | cut -d= -f2)
YEAR=$(date +%Y)
MONTH=$(date +%m)
NEWLOG="/var/log/dpkg-${DISTRO}-${YEAR}-${MONTH}.log"
[ ! -f "$NEWLOG" ] && touch "$NEWLOG" && chown root:root "$NEWLOG" && 
chmod 644 "$NEWLOG"
# Atomic symlink switch
ln -sfT "$NEWLOG" /var/log/dpkg.log

# compression of OLD logs only:
find /var/log -name 'dpkg-*.log' -not -newermt "$(date +%Y-%m-01)" -exec 
gzip {} \;

3. Disable logrotate:

mv /etc/logrotate.d/dpkg /etc/logrotate.d/dpkg.disabled


## Usage example

zgrep upgrade /var/log/dpkg.log                     # Current month
zgrep upgrade /var/log/dpkg-trixie-2025-10.log      # Trixie, October 
2025 history only
zgrep upgrade /var/log/dpkg-*.log                   # All history
zgrep upgrade /var/log/dpkg-trixie-*.log            # Trixie only and 
everything since release
zgrep upgrade /var/log/dpkg-trixie-2025*.log        # Trixie and year 
2025 history only
rm /var/log/dpkg-bookworm-*.log                     # Delete Bookworm

## Migration from current system

for f in /var/log/dpkg.log*; do
     DISTRO=$(grep '^VERSION_CODENAME=' /etc/os-release | cut -d= -f2)
     CREATEDATE=$(stat -c %y "$f" | cut -d' ' -f1 | sed 's/\./-/g')
     YEAR=${CREATEDATE:0:4}
     MONTH=${CREATEDATE:5:2}
     mv "$f" "/var/log/dpkg-${DISTRO}-${YEAR}-${MONTH}.log"
done
ln -sf /var/log/dpkg-$(grep '^VERSION_CODENAME=' /etc/os-release | cut 
-d= -f2)-$(date +%Y-%m).log /var/log/dpkg.log


## Addressing Concerns

Q: What about wrong system time?
A: systemd-timer (`OnCalendar=monthly`) or `hwclock`-based fallback

Q: Race conditions?
A: `ln -sfT` + file existence check = atomic

Q: Backward compatibility?
A: `/var/log/dpkg.log` works exactly as before

Q: Embedded systems?
A: No logrotate parsing/rotation → less complexity

Q: Alternative naming?
A: `/var/log/dpkg-current.log` more explicit (optional migration path)

## Why superior to logrotate

Feature                         | logrotate        | Symlink
--------------------------------|------------------|--------
Dependencies                    | cron + logrotate | cron only
History                         | 12 months        | Unlimited + Distro
Cleanup of time specific logs   | Complex          | rm dpkg-trixie-*
Distro tracking                 | None             | Native in filename
Size/Month                      | ~50kB            | ~15kB gz for last 
months and older
dpkg changes                    | None             | None

## Request

1. Ship monthly cron + symlink setup in dpkg package
2. Document in `dpkg(1)` manpage
3. Disable `/etc/logrotate.d/dpkg` by default
4. Optional: Migrate file naming from dpkg.log to dpkg-current.log over 
time, because its name is more intuitive (clearly indicating the current 
log)
5. Optional: Migrate location of dpkg-*.log files to /var/log/dpkg/ 
(dpkg.log symlink can stay in /var/log/)

This eliminates 25+ year old logrotate complexity while preserving all
compatibility. Modern storage makes unlimited history practical.

-- System Information:
Debian GNU/Linux 13 (trixie)
dpkg 1.22.21

Regards,
Oliver C.