prometheus - The Prometheus monitoring server

Options you will use

--config.file

Default /etc/prometheus/prometheus.yml.

--web.enable-lifecycle

Enables POST /-/reload and /-/quit. OFF by default (Debian/Ubuntu ARGS=""), so use systemctl reload prometheus (SIGHUP).

--storage.tsdb.retention.time

How long to keep data. Default 15d.

--query.lookback-delta

How far back an instant selector looks for the latest sample. Default 5m.

--config.file=FILE

Prometheus configuration file path (default prometheus.yml; /etc/prometheus/prometheus.yml on Ubuntu).

--storage.tsdb.path=DIR

Base path for metrics storage (default data/).

--storage.tsdb.retention.time=DURATION

How long to retain samples (default 15d).

--storage.tsdb.retention.size=SIZE

Maximum bytes of blocks to keep (e.g. 50GB); the oldest go first.

--web.listen-address=ADDR

Address to listen on for the UI, API and telemetry (default 0.0.0.0:9090).

--query.lookback-delta=DURATION

How far back an instant selector looks for the latest sample (default 5m).

--web.enable-remote-write-receiver

Accept remote write requests on /api/v1/write.

Examples

$ sudo systemctl reload prometheus

reload config + rules; a broken config is rejected and the old one keeps running

$ journalctl -u prometheus -n 20

see whether the reload worked

Gotchas

• Ubuntu 26.04 ships prometheus 2.53.5 (the 2.53 LTS line). Upstream is on 3.x; the differences that matter here are noted in the lessons.