---
type: operations
title: Cron Lifecycle
description: How entrypoint.sh validates env, renders /etc/cron.d/tenbackward from RUN_AT/TZ, and hands off to cron -f.
tags: [cron, entrypoint, ops]
timestamp: 2026-08-04T17:51:00Z
---

# Purpose

`entrypoint.sh` is the first process inside the container. Its job is
to refuse to boot when something is wrong with env config and to
materialise a cron file from the templated values.

# Sequence

1. Set `DEBIAN_FRONTEND=noninteractive`.
2. Set `TZ` (default `Europe/Berlin`) and link `/etc/localtime` if
   `/usr/share/zoneinfo/${TZ}` exists and `/etc/localtime` does not.
3. Iterate over `required_vars`. Any empty variable aborts with
   `ERROR: missing required environment variable(s): ...` and exits
   `1`. The current required set is listed in
   [Environment Variable Setup](/operations/environment-setup.md).
4. Validate `RUN_AT` against
   `^([01][0-9]|2[0-3]):[0-5][0-9]$`. Invalid input exits `1` with
   `ERROR: RUN_AT='X' must be in HH:MM (24-hour) format`.
5. Render `/etc/cron.d/tenbackward` into a `mktemp` file with:

    ```cron
    SHELL=/bin/bash
    PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
    TZ=${TZ}
    ${minute} ${hour} * * * cd /app && /usr/local/bin/python -m tenbackward >> /app/data/cron.log 2>&1
    ```

6. Install the rendered file with mode `0644`, root:root.
7. Run `crontab/install-cron.sh /etc/cron.d/tenbackward`. The helper
   refuses files that still contain the `__RUN_AT__` placeholder and
   files that do not start with an `^[A-Z_]+=` cron env line.
8. Print a one-line confirmation: `tenbackward: starting cron
   (RUN_AT=..., TZ=...)`.
9. `exec cron -f`.

# Output Files

| Path                         | Owner / Mode | Purpose                                              |
|------------------------------|--------------|------------------------------------------------------|
| `/etc/cron.d/tenbackward`    | root / 0644  | The rendered cron file.                              |
| `/app/data/cron.log`         | container user / append | `python -m tenbackward` stdout+stderr.       |
| `/app/data/posted.json`      | container user / rw     | Persisted state from `tenbackward.state`.    |

# Cron Helpers

| File                            | Purpose                                                                |
|---------------------------------|------------------------------------------------------------------------|
| `crontab/tenbackward.cron`      | Static template (env + PATH) shipped in the image.                     |
| `crontab/install-cron.sh`       | Validates and installs a rendered cron file with mode 0644.            |

# Operator Recipes

* **Trigger a manual run** without waiting for the cron tick:

    ```bash
    docker compose exec tenbackward /usr/local/bin/python -m tenbackward
    ```

* **Inspect the rendered cron file** (the file the container actually
  installed):

    ```bash
    docker compose exec tenbackward cat /etc/cron.d/tenbackward
    ```

* **Tail the structured logs** produced by the bot:

    ```bash
    docker compose exec tenbackward tail -n 100 /app/data/cron.log
    ```

    Expect one JSON object per line (`startup`, optional `run_complete`,
    or `pipeline_error` / `pipeline_failed`).

# Build Script Notes

`build.sh` now `cd`s into its own script directory (so it works
no matter where it is invoked from) and, when possible, symlinks
itself to `/usr/local/bin/build.sh` so the build can also be run as a
plain `build.sh` command inside the build context. The symlink is a
best-effort `|| true`, so a read-only filesystem will not break the
build.

# Related

* [Environment Variable Setup](/operations/environment-setup.md)
* [Pipeline Runner](/architecture/pipeline-runner.md)
* [Logging & Run Summary](/architecture/logging.md)