Stopping logs filling the disk.
WHAT ROTATION DOES
Renames the current log, starts a new one, compresses old ones, and deletes the oldest.
WHY IT IS NECESSARY
Logs grow without limit, and a full disk stops everything.
WHERE IT IS CONFIGURED
A main configuration file, plus one file per service in a directory.
WHAT THE KEY SETTINGS ARE
How often to rotate How many to keep Whether to compress What to do after rotating
WHAT THE POST-ROTATE STEP IS FOR
Telling the service to reopen its log file.
WHY THAT MATTERS
Without it the service keeps writing to the renamed file, and the new one stays empty.
WHAT THAT LOOKS LIKE IN PRACTICE
A compressed old log that keeps growing, and a current log of zero bytes.
WHAT TO PREFER WHERE SUPPORTED
Copying and truncating, which avoids the problem entirely.
HOW TO TEST A CONFIGURATION
Run rotation in debug mode, which reports what it would do.
WHY TEST
An error in one file can stop rotation for everything.
WHAT TO CHECK PERIODICALLY
That rotation is actually running That old logs are being removed
WHAT TO WATCH FOR
Application logs outside the system's rotation, which are frequently forgotten.
WHAT TO DO ABOUT A LOG ALREADY ENORMOUS
Truncate it rather than deleting it, if the service holds it open.
