Basics of at

at runs a command once at a specified time.

Unlike cron, it is for one-time jobs.

1. Basic syntax

at TIME

Then type the command:

at 15:30
echo "hello"

Press Ctrl+D to submit.

2. Examples

Run in 5 minutes

at now + 5 minutes

echo "done"

Run in 1 hour

at now + 1 hour

Run at a specific time

at 18:00

notify-send "Time!"

Run tomorrow

at 09:00 tomorrow

3. One-line commands

Use at with a pipe:

echo 'notify-send "Done!"' | at 18:00

Or:

echo 'shutdown -h now' | at 23:00

4. List scheduled jobs

atq

Example:

3       Thu Aug 20 18:00:00 2026 a marvin
4       Thu Aug 20 19:30:00 2026 a marvin

5. Delete a job

Get the job ID:

atq

Then:

atrm 3

6. Useful time formats

at 15:30
at 3:30 PM
at now + 10 minutes
at now + 2 hours
at now + 1 day
at midnight
at noon
at tomorrow

7. at vs cron

Example:

at 18:00

Run once at 18:00.

0 18 * * *

Run every day at 18:00.

8. Check if at is running

On systemd:

systemctl status atd

Start it:

sudo systemctl enable --now atd

9. Simple alarm

echo 'notify-send "Alarm!"' | at now + 30 minutes

Or play a sound:

echo 'paplay /path/to/alarm.wav' | at 07:00

Mental model

at
 │
 ├── schedule a command
 │
 ├── atq       → list jobs
 │
 └── atrm ID   → remove job

at = one-shot cron.