# Cron Job Helper — Manual

> Complete walkthrough of the Cron Job Helper: cron syntax, the visual builder, presets, plain-text preview, web cron generator, CMS recipes and Docker/DDEV.

Source: https://www.jpkc.com/db/en/tools/cron/manual/

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This manual describes the **Cron Job Helper** in full: the cron syntax it understands, each of the five tabs, and the commands they produce. The interface is in English, so the tab and field labels below are quoted as they appear in the tool.

## Cron syntax: five fields

A classic cron expression consists of **five space-separated fields** followed by the command to run. The tool shows this as a diagram in the *Reference* tab:

```
┌─────────── minute (0–59)
│ ┌───────── hour (0–23)
│ │ ┌─────── day of month (1–31)
│ │ │ ┌───── month (1–12)
│ │ │ │ ┌─── day of week (0–6, Sun=0)
│ │ │ │ │
* * * * *  command to execute
```

The allowed values and special characters per field:

| Field | Values | Special chars |
| --- | --- | --- |
| Minute | 0–59 | `* , - /` |
| Hour | 0–23 | `* , - /` |
| Day of Month | 1–31 | `* , - / ? L W` |
| Month | 1–12 or JAN–DEC | `* , - /` |
| Day of Week | 0–6 or SUN–SAT | `* , - / ? L #` |

For the day of week, **Sunday = 0**. Some cron implementations also accept `7` for Sunday and the three-letter names (`SUN`, `MON`, …); the *Manual Input* field also accepts names such as `sun`.

### The special characters

The tool distinguishes the standard Vixie-cron characters from the extended **Quartz** characters (`?`, `L`, `W`, `#`), which the *Reference* tab explicitly marks as Quartz — they work in Java/Quartz schedulers but **not** in plain Unix `cron`:

| Char | Meaning | Example |
| --- | --- | --- |
| `*` | any value | `* * * * *` → every minute |
| `,` | value list | `0,15,30,45` → at minute :00 :15 :30 :45 |
| `-` | range | `1-5` (day of week) → Mon–Fri |
| `/` | step / interval | `*/5` → every 5 units |
| `?` | no specific value (Quartz) | `0 12 ? * MON` |
| `L` | last (Quartz) | `L` in day-of-month → last day |
| `W` | nearest weekday (Quartz) | `15W` → nearest weekday to the 15th |
| `#` | nth weekday (Quartz) | `5#3` → 3rd Friday |

### Special strings

Instead of five fields, cron also accepts `@` shortcuts. The tool recognises them in *Manual Input* and expands them:

| String | Equivalent | Meaning |
| --- | --- | --- |
| `@reboot` | — | once at system startup |
| `@yearly` / `@annually` | `0 0 1 1 *` | once a year, January 1st |
| `@monthly` | `0 0 1 * *` | once a month, on the 1st at midnight |
| `@weekly` | `0 0 * * 0` | once a week, Sunday midnight |
| `@daily` / `@midnight` | `0 0 * * *` | once a day at midnight |
| `@hourly` | `0 * * * *` | once an hour |

`@reboot` has no calculable schedule — so the *Next Scheduled Runs* show no times, just a note that the job only runs at system startup.

## Tab 1 — Builder

The **Builder** is the heart of the tool. At the top sits the *Cron Expression*: the current expression (default `* * * * *`), the field labels below it, and a **plain-text description** of what the expression does. A **Copy** button copies the expression to the clipboard.

### The field cards

Below that, each of the five fields gets a card (Minute, Hour, Day of Month, Month, Day of Week) with a dropdown for the **mode**:

- **Every <field>** — every value (`*`).
- **Every N <field>s (*/N)** — step: a number input appears, producing `*/N`.
- **Specific value** — a fixed single value; a number input within the field's allowed range.
- **Range (A–B)** — a range; two *From*/*to* inputs produce `A-B`.
- **List (A,B,C)** — a comma-separated list, e.g. `0,15,30,45`.

Any change instantly updates the expression above, the plain-text description and the list of next runs.

### Manual Input

Prefer typing the expression? Use the **Manual Input** field. It accepts five space-separated fields (e.g. `*/5 * * * *`) or a special string (`@daily`). If the input is invalid (fewer than five fields), a red error appears. A valid input syncs the field cards back, so the builder and the text input always show the same state.

### Quick Presets

On the right sit 16 **Quick Presets** as buttons that set an expression with one click:

Every minute (`* * * * *`), Every 5 min (`*/5 * * * *`), Every 15 min (`*/15 * * * *`), Every 30 min (`*/30 * * * *`), Every hour (`0 * * * *`), Every 2 hours (`0 */2 * * *`), Every 6 hours (`0 */6 * * *`), Every 12 hours (`0 */12 * * *`), Daily midnight (`0 0 * * *`), Daily 3 AM (`0 3 * * *`), Weekly (Sun) (`0 0 * * 0`), Weekly (Mon) (`0 0 * * 1`), Monthly 1st (`0 0 1 * *`), Yearly Jan 1st (`0 0 1 1 *`), Weekdays 9 AM (`0 9 * * 1-5`) and Weekends (`0 0 * * 6,0`).

### Next Scheduled Runs

Also on the right, the tool computes the **next run times** (up to eight) from the current expression — with date, time and a relative label (`in 5 min`, `in 2h`, `in 3d …`). It looks up to one year ahead; if it finds no match in that window, it says so. This preview is a **client-side estimate** based on the browser clock (local time zone), not a server run — see the [Tips](https://www.jpkc.com/db/en/tools/cron/tips/) on the time-zone question.

## Tab 2 — Web Cron

The **Web Cron** tab builds a cron job that **calls a URL over HTTP** instead of running a local script — handy for shared hosting or CMS tasks. You configure on the left; on the right, two outputs update live: the *Generated Crontab Line* (full line with schedule) and *Command only* (just the command).

The configuration fields:

- **Tool** — `curl (recommended)` or `wget`.
- **URL to call** — the address to request.
- **Cron schedule** — the schedule (default `*/15 * * * *`); build it in the *Builder* and paste it here.
- **Timeout (sec)** — default 30, range 5–300. Becomes `--max-time` (curl) or `--timeout=` (wget).
- **HTTP Method** — `GET` or `POST` (`POST` → `-X POST`).
- **Log file path** (optional) — appends `>> "file" 2>&1`.
- **User-Agent** (optional) — `-A` (curl) or `--user-agent=` (wget).
- **HTTP Auth User / Pass** (optional) — `-u "user:pass"` (curl) or `--user`/`--password` (wget).
- **Silent mode** (on by default) — suppresses output (`-s` for curl, `-q` for wget). With silent off, curl additionally appends `-w "%{http_code}"` to print the HTTP status.
- **Skip SSL verification** — `-k` (curl) or `--no-check-certificate` (wget); for testing only.

A typical generated curl line looks like this:

```
*/15 * * * *  curl -s --max-time 30 -o /dev/null "https://example.com/cron/run" > /dev/null 2>&1
```

The tab also has a **Web Cron Tips** block with six pointers — among them: always use `-s` with curl on shared hosting (otherwise cron emails the full response on every run), redirect output to a log file, protect the URL with a token/IP restriction/basic auth, set a timeout, check the HTTP status, and always use HTTPS.

## Tab 3 — CMS & Frameworks

Here the tool offers ready-made crontab recipes for five systems, each with a copy button. The message everywhere: replace or trigger the built-in or pseudo-scheduled scheduler with a **real system cron**.

### WordPress

WordPress uses **WP-Cron**, which fires on page loads — unreliable on low-traffic sites. Recommendation: disable WP-Cron in `wp-config.php` via `define( 'DISABLE_WP_CRON', true );` and replace it with a real cron, ideally via **WP-CLI** (`wp cron event run --due-now …`), alternatively via curl on `wp-cron.php`.

### TYPO3

TYPO3 uses the **Scheduler** extension, which a real cron must trigger. The recommended path is the **TYPO3 CLI** (`vendor/bin/typo3 scheduler:run`, v10+); for older versions, the eID method via curl. The tool warns that the eID method is deprecated and removed in v12.

### Drupal

Drupal uses **cron hooks** (`hook_cron()`), triggered via **Drush** (`vendor/bin/drush cron`) or via curl with the **cron key** (from *Administration → Configuration → System → Cron*). The tool recommends disabling the built-in *Automated Cron* module for full control.

### Laravel

Laravel's **Task Scheduler** needs only **one** crontab line (`php artisan schedule:run`, every minute) — all tasks are defined in code (`app/Console/Kernel.php`, or `routes/console.php` from v9). The tab shows example task definitions and the foreground mode `schedule:work`.

### Symfony

Symfony uses **Console Commands**, one crontab line per command (`bin/console …`). From Symfony 6.3 there is the **Scheduler** component, driven by a worker (`messenger:consume scheduler_default`). The tool's note: always add `--no-ansi` and `--no-interaction` when running from cron.

### General Best Practices

A dedicated block collects seven general rules: use **absolute paths** (cron has a minimal `$PATH`, so `/usr/bin/php` instead of `php`); specify the **user** in `/etc/crontab` or `/etc/cron.d/`; **redirect output** (`>> /var/log/cron.log 2>&1` or `/dev/null`); **lock** against overlap (`flock`); **test the command manually** as the cron user first; prefer **`cron.d` over `crontab`** (file-based, version-controllable); and mind the **time zone** (`CRON_TZ=Europe/Berlin` at the top of the crontab).

## Tab 4 — Docker / DDEV

This tab collects patterns for cron in containers.

### Docker & Podman

Three approaches plus Podman:

- **Option 1 — cron inside the container:** install a cron daemon in the `Dockerfile` (e.g. `dcron` on Alpine), copy in the `crontab` file and start `crond` in the entrypoint. Tip: write output to `/proc/1/fd/1` so it shows up in the Docker stdout log.
- **Option 2 — dedicated cron container:** in Docker Compose, a separate service with the same image/volume and `command: ["crond", "-f", "-l", "2"]`.
- **Option 3 — `docker exec` from the host:** the host crontab calls `docker exec -t my_app …` into the running container.
- **Podman (rootless):** the same via `podman exec`; plus `loginctl enable-linger $USER` so user services and cron survive logout.

### DDEV

Three DDEV variants plus CMS examples:

- **Option 1 — host cron + `ddev exec`:** only works while the project is running (`ddev start`) — the tool suggests a `ddev describe | grep running` check.
- **Option 2 — custom DDEV service (recommended):** `.ddev/docker-compose.cron.yaml` with a loop container (`while true; … sleep 60`).
- **Option 3 — DDEV hook (post-start):** a `post-start` hook in `.ddev/config.yaml`; simple, but the process ends on container restart.
- Plus ready-made lines for **WordPress in DDEV** (`ddev wp cron event run --due-now`) and **TYPO3 in DDEV** (`ddev typo3 scheduler:run`).

A **Container Cron Tips** block adds: avoid cron inside the container where possible (prefer the dedicated container), log to stdout, set the **time zone** (`TZ=Europe/Berlin`, otherwise UTC), use health checks, and use the same scheduler approach locally (DDEV) and in production.

## Tab 5 — Reference

A pure cheat sheet, usable any time without input: the **syntax diagram** shown above, the **field** and **special-character** tables, the **special-string** table, a **Common Examples** table, **Useful Commands** (`crontab -e`, `crontab -l`, `crontab -r`, `crontab -u www-data -e`, `ls /etc/cron.d/`, `systemctl status cron`, `grep CRON /var/log/syslog`, `run-parts /etc/cron.hourly`) and the **MAILTO** section.

### MAILTO — email notifications

By default, cron emails any output (stdout/stderr) of a job to the local system user. The `MAILTO` variable at the top of the crontab controls this:

| Setting | Effect |
| --- | --- |
| `MAILTO=""` | disables all cron emails globally |
| `MAILTO="admin@example.com"` | sends output to an address |
| `MAILTO="root"` | sends to local root (default) |

The tool contrasts the two mechanisms: `MAILTO=""` suppresses email **globally** for the whole crontab, while `> /dev/null 2>&1` suppresses output **per command** and also prevents a process from blocking on a full mail queue. For web cron jobs, combining both is the most robust.

---

For the audiences and the big picture, see the [overview](https://www.jpkc.com/db/en/tools/cron/). Concrete expressions are in the [examples](https://www.jpkc.com/db/en/tools/cron/examples/), the classic pitfalls in the [tips & tricks](https://www.jpkc.com/db/en/tools/cron/tips/). Try it all directly in the [tool](https://www.jpkc.com/tools/cron/).