# flatcar-crontab

A `crontab` command for [Flatcar Container Linux](https://www.flatcar.org/), written in bash, that needs nothing beyond what Flatcar ships.

Flatcar has no cron, and no official or sysext-bakery extension provides one. This wrapper lets scripts that call `crontab` run unchanged: each crontab line becomes a systemd `--user` timer and service for the calling user.

## Install

```bash
sudo install -D -m 0755 crontab /opt/bin/crontab
sudo loginctl enable-linger core   # the user that owns the crontab
```

`/opt/bin` must be on the `PATH` of whatever calls `crontab`. Linger keeps the user's timers running without a login session.

## Usage

```bash
crontab FILE      # replace the crontab from a file
crontab -         # replace the crontab from stdin
crontab -l        # print it
crontab -r        # remove it
```

There is no `crontab -e`: edit a file and install it.

## Checking jobs

```bash
systemctl --user list-timers --all
journalctl --user -u crontab-job-3
```

Jobs are numbered in crontab order.

## Files

| Path | Content |
|---|---|
| `~/.config/crontab-timers/crontab` | The installed crontab |
| `~/.config/crontab-timers/jobs/N.sh` | The command of job N |
| `~/.config/systemd/user/crontab-job-N.{timer,service}` | Generated units |

## Supported schedules

Five fields, each `*`, `*/n`, a value, `a-b`, `a-b/n` or a comma list. Month and weekday names work. Weekdays do not accept steps, and a weekday range must be ascending (`0-2`, not `5-1`).

These are refused, and the installed crontab is left as it was:

- `@daily` and other `@` schedules
- `VAR=value` lines
- Unescaped `%` (`\%` is accepted and becomes `%`)
- Restricting both day-of-month and weekday: cron ORs them, systemd ANDs them

## Differences from cron

- A run that comes due while the previous one is still active is skipped, not started alongside it.
- There is no mail; capture job output yourself, for example with `logger`.
- Runs missed while the machine was off are not caught up, as in cron.
- Times follow the host's time zone, which is normally UTC on Flatcar.