Calculate the exact execution time for a one-off job scheduled with the at command.
The `at` command schedules a one-time job for a future point in time (unlike cron's recurring schedule), queued and executed by the atd daemon once the specified time arrives — the job runs exactly once and is then removed from the queue. This calculator converts a relative delay (e.g. '90 minutes from now') into the absolute wall-clock execution time and a human-readable countdown, along with the equivalent `at` command syntax you'd actually run.
Execution time
execution_time = current_time + delay_amount × unit_to_ms_multiplier
cron is for recurring schedules (run every day at 2am, every 15 minutes, etc.), defined declaratively via a cron expression. `at` is for one-off, single-execution jobs scheduled relative to or at an absolute future time — after it runs once, the job is gone, unlike a crontab entry which persists and fires repeatedly.
Yes — `at` merely queues the job (typically under /var/spool/at/); the atd daemon must be running and polling that queue to actually execute jobs when their time arrives. On many distros atd is enabled by default, but it's worth confirming with `systemctl status atd` if a scheduled job doesn't run.
Yes — `atq` lists all pending jobs with their job number and scheduled time, and `atrm <job_number>` cancels a specific pending job before it executes.