Writing Line Protocol

arcctl write POSTs line-protocol records to Arc's /api/v1/write/line-protocol endpoint. Body is streamed — large files / pipes never buffer in memory — so cat huge.lp | arcctl write works at line-rate.

Quick reference

# Stdin pipe — most common in CI / log forwarders / quick experiments
echo "cpu,host=server-1 value=42.5 $(date +%s)000000000" | arcctl write

# From a file
arcctl write -f payload.lp --database metrics

# Explicit precision (default is nanoseconds)
echo "cpu v=1 1700000000" | arcctl write --precision s

Input

arcctl write reads its body from one of:

1. -f file.lp flag — opens the file with os.Open and streams it through to the POST body. The file handle is closed when the write completes.
2. Stdin — used when -f is not given. No buffering; bytes flow through as they arrive.

Unlike arcctl query, arcctl write does not error on an empty TTY stdin — typing line protocol interactively is a (rare) supported workflow. An empty body is accepted by the server as a no-op (OK, exit 0).

Line protocol

Arc accepts the standard InfluxDB line protocol:

<measurement>,<tag1>=<value>,<tag2>=<value> <field1>=<value>,<field2>=<value> <timestamp>

• Measurement — required, the "table" name in Arc
• Tags — optional, comma-separated key=value pairs (string-only, schemas inferred)
• Fields — required, at least one numeric/string/bool value
• Timestamp — optional; if omitted, Arc applies wall-clock-at-receive

Example:

cpu,host=server-1,region=us-east value=42.5,temp=68.0 1700000000000000000
mem,host=server-1 used=8.5,total=16.0 1700000000000000000

Precision

--precision tells the server how to interpret bare-integer timestamps:

Value	Unit
ns (default)	nanoseconds since epoch
us	microseconds
ms	milliseconds
s	seconds

echo "cpu v=1 1700000000" | arcctl write --precision s
echo "cpu v=1 1700000000000" | arcctl write --precision ms

arcctl validates the precision flag client-side before the request goes out, so a typo like --precision furlong fails fast:

$ arcctl write --precision furlong < x.lp
Error: invalid --precision "furlong" (must be one of ns, us, ms, s)

Database selection

The default database comes from the active connection's default_database. Override per-call:

arcctl write -f payload.lp --database metrics

If neither the connection default nor --database is set, Arc applies its own server-side default (default).

Streaming behavior

arcctl write does NOT buffer the body. This matters for:

• Large files — arcctl write -f /var/log/lp/all-day.lp streams without loading the file into RAM.
• Continuous pipes — tail -F app.log | parser | arcctl write keeps memory flat while ingesting at line-rate.
• HTTP timeout — --timeout applies to the whole request. A 10 GB file + the default 60s timeout will time out before completion. For large writes, raise --timeout:

arcctl write -f huge.lp --timeout 30m

Exit codes

Code	Meaning
0	Server returned 204 No Content (success)
1	Any failure: bad flags, network error, server error (4xx/5xx)

On success, arcctl write prints OK to stdout. On failure, the server's error message is surfaced:

$ echo "garbage" | arcctl write
Error: arc: malformed line at offset 0 (HTTP 400)

Common patterns

Backfill from a file

arcctl write -f historical.lp --database backfill --precision ms

Continuous ingestion from a log tail

tail -F /var/log/app.log | \
  awk '{ printf("log,host=%s msg=\"%s\" %d000000000\n", "myhost", $0, systime()) }' | \
  arcctl write --database logs

Ad-hoc connection (no profile)

echo "metric v=1" | arcctl write \
  --endpoint https://arc.staging.example.com \
  --token YOUR-TOKEN \
  --database metrics

CI-friendly with env vars

ARC_ENDPOINT=https://arc.x.example.com ARC_TOKEN=YOUR-TOKEN \
  arcctl write -f payload.lp --database metrics

See Connection management for the full precedence rules.