Ship a logrotate rule for the run log

/var/log/dist-upgrade.log grows across runs: rotate weekly, keep 8
compressed, mode 0640 root:root. Uses create rather than copytruncate
since the script reopens the file on each run.

3 files changed, 19 insertions, 2 deletions

diff --git a/AGENTS.md b/AGENTS.md
index 5024c4d..723408e 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -11,6 +11,10 @@ Run all of these before calling a change done:
     ./dist-upgrade --self-test
     shellcheck --exclude=SC2218 dist-upgrade
 
+If `logrotate` is available, the shipped rule can be checked with:
+
+    logrotate -d logrotate.d/dist-upgrade
+
 SC2218 is a shellcheck 0.11.0 false positive: it flags a function called on the
 left of a pipe inside another function definition (`b() { a | cat; }`), even
 when `a` is defined above. Keep it excluded; do not restructure the pipeline to
@@ -21,8 +25,9 @@ silence it.
 - Do not run the script itself, or any `slackpkg` command, in this repo. It
   performs a real system upgrade and only makes sense on the user's Slackware
   box as root.
-- Do not add config, cache or log files. The script is self-contained and
-  configured through the `INITRD` environment variable.
+- Do not add runtime config, cache or log files. The script is self-contained
+  and configured through the `INITRD` and `LOG` environment variables; the only
+  config it ships is `logrotate.d/dist-upgrade`.
 
 ## Conventions
 
diff --git a/README.md b/README.md
index 63e35b3..86f6098 100644
--- a/README.md
+++ b/README.md
@@ -25,6 +25,9 @@ Environment:
 - `LOG` append the whole run, slackpkg output included, to this file
   (default `/var/log/dist-upgrade.log`; set it empty to disable)
 
+A logrotate rule for that log ships in `logrotate.d/dist-upgrade`; install it
+to `/etc/logrotate.d/`.
+
 ## What it does
 
 1. Snapshots the current initrd's kernel version and module list.
diff --git a/logrotate.d/dist-upgrade b/logrotate.d/dist-upgrade
new file mode 100644
index 0000000..30af922
--- /dev/null
+++ b/logrotate.d/dist-upgrade
@@ -0,0 +1,9 @@
+/var/log/dist-upgrade.log {
+	weekly
+	rotate 8
+	missingok
+	notifempty
+	compress
+	delaycompress
+	create 0640 root root
+}