How to run a command at a specific time once using at?
Jun 26, 2025 am 12:12 AM
To run a one-time timing task using the at command in Linux, first make sure that the at service is installed and started. 1. Check whether to install: Use which at in Debian/Ubuntu and RHEL/CentOS/Fedora; 2. If not installed, install at; 3. Make sure the atd service is running and enable power-on self-start if necessary. The basic syntax is echo "command" | at time or press Ctrl D to end after entering the command directly. Supports a variety of time formats such as now 5 minutes, 10:00 AM tomorrow, etc. Use atq to view the task list and use atrm to add task number to cancel the task. Notes include using absolute paths, processing of email notifications and permission management.
To run a command at a specific time just once, the at command in Linux is your go-to tool. It allows you to schedule tasks without having to set up recurring jobs like with cron.
Make Sure at Is Installed and Running
Before using at , check if it's installed on your system. Most modern Linux distributions come with it pre-installed, but some might not. You can verify this by typing:
- On Debian/Ubuntu:
which at - On RHEL/CentOS/Fedora:
which at
If it's not there, install it:
- Ubuntu/Debian:
sudo apt install at - RHEL/CentOS:
sudo yum install atorsudo dnf install at
Also, make sure the atd service is running:
- Check status:
systemctl status atd - Start it if needed:
sudo systemctl start atd - Enable it to run at boot:
sudo systemctl enable atd
Basic Syntax and Usage
The general syntax is simple:
echo "your-command-here" | at your-time-here
For example, to run a script called backup.sh at 10:30 PM today:
echo "/home/user/scripts/backup.sh" | at 22:30
You can also type the command directly after running at :
at 22:30 > /home/user/scripts/backup.sh > <Ctrl D>
Time formats are flexible:
-
now 5 minutes -
tomorrow -
22:30 -
10:00 AM tomorrow -
10:00 AM next Friday
View and Manage Scheduled Jobs
Once a job is scheduled, you can list all pending jobs with:
atq
This will show something like:
4 Wed Jul 10 22:30:00 2024 a user
If you need to cancel a job before it runs:
attrm [job number]
Each job has a number assigned when it's queued. Use atq to find that number first.
Note: Once a job runs, it won't show up in atq anymore — unless it failed and was moved to batch processing.
Some Common Gotchas
- Environment variables – The environment when
atruns may be different from your current shell. Best practice is to use absolute paths for commands and files. - Email notifications – By default, output (stdout and stderr) of the command is emailed to the user. If you don't want this, redirect output:
echo "/path/to/script.sh > /dev/null 2>&1" | at now 1 minute
- Permissions – Regular users can use
atonly if they're allowed. Root can manage/etc/at.allowand/etc/at.denyto control access.
So yes, at is great for one-off tasks, but keep these small details in mind to avoid surprises.
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