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chartjs2img

Environment variables (CLI) ​

Running chartjs2img render reads a small set of environment variables — mostly to locate Chromium and to tune the render budget. Variables specific to the HTTP server (PORT, HOST, API_KEY) have no effect here; see HTTP server → Environment variables for those.

VariableDefaultDescription
CHROMIUM_PATH(none)Explicit path to a Chromium / Chrome executable. Wins over the auto-detection chain.
PLAYWRIGHT_BROWSERS_PATH(none)Override the Playwright cache directory searched during detection.
MAX_RENDER_TIME_SECONDS30Upper bound for a single render (applied to page.goto and waitForFunction).
PAGE_TIMEOUT_SECONDS(derived)Override the safety-net force-close timer. Default: MAX_RENDER_TIME_SECONDS * 2 + 10s.
CONCURRENCY8Not exercised by one-shot render, but respected by chartjs2img examples batch mode.

The cache variables (CACHE_MAX_ENTRIES, CACHE_TTL_SECONDS) are also read at startup, but the cache lives only as long as the process — so a single one-shot render call cannot benefit from cache hits. They are effectively a server concern.

Setting them ​

Per-command ​

bash
CHROMIUM_PATH=/usr/bin/chromium-browser chartjs2img render -i chart.json -o chart.png

Per-shell ​

bash
export CHROMIUM_PATH=/usr/bin/chromium-browser
export MAX_RENDER_TIME_SECONDS=60

chartjs2img render -i chart.json -o chart.png

In CI / systemd ​

Set them alongside your job definition. On GitHub Actions:

yaml
- name: Render charts
  env:
    CHROMIUM_PATH: /usr/bin/chromium-browser
    MAX_RENDER_TIME_SECONDS: 60
  run: chartjs2img render -i chart.json -o chart.png

When to tune ​

CHROMIUM_PATH ​

Set it when the auto-detection chain can't find a browser you know is installed — Linux ARM64 is the common case because the Chrome for Testing auto-download does not publish linux-arm64 builds. See Install → Linux ARM64.

MAX_RENDER_TIME_SECONDS ​

Raise it when you legitimately need long renders — e.g. a very large force-directed graph or a CDN cold start on a slow network. The default 30 s covers every bundled example several times over.

PAGE_TIMEOUT_SECONDS ​

Leave it alone unless you see a Safety net fired after Xms warning in stderr without the render actually hanging. If that happens the derived default is too tight — raise it (or increase MAX_RENDER_TIME_SECONDS, which re-derives the safety net).

See also ​

  • Install — Chromium detection order and linux-arm64 notes.
  • Error feedback — interpreting render-time warnings on stderr.
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