handle logrotate copytruncate and dateext edge cases when rotating logs for daemons that can't be told to reopen their log file
domain: man7.org · 5 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗
Steps
For daemons with no signal/reload hook to reopen log files, use the `copytruncate` directive instead of the default rename-then-recreate rotation.
Understand that copytruncate copies the file then truncates the original in place, rather than moving it, so the `create` directive has no effect and should be omitted when copytruncate is used.
Enable dated rotated filenames with `dateext`, and set a custom, lexically-sortable format with `dateformat`, restricted to %Y, %m, %d, %s in year-month-day order (e.g., -%Y%m%d).
Combine `size` rotation criteria with `dateext` carefully: if size-based rotation can trigger more than once per day, the second rotation collides with the first day-stamped filename and logrotate errors instead of overwriting.
Test a configuration safely before production use with `logrotate --debug <config>` (dry run, no changes applied) and `logrotate --force <config>` to force an immediate real rotation for verification.
Known gotchas
copytruncate has a small race window between the copy and the truncate where log lines written by the still-running daemon in that gap are lost; it's a lossy tradeoff, not a perfect substitute for reopen-on-signal.
A dateformat that doesn't sort lexically the same as chronologically breaks logrotate's own logic for identifying and pruning the oldest rotated files under `rotate N`.
Combining dateext with multiple rotations in a single day produces a naming collision that causes the second rotation to fail rather than append a disambiguating suffix by default.
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