at Command Overview
`at` creates a job that executes only once at a user-specified time. The job is queued along with the user's shell environment and runs in the background at the designated time. After entering the command, you can press Ctrl+D to terminate and schedule the job.
Advantages of using at
- Allows intuitive time specification without complex time settings.
- More convenient than `crontab` for scheduling tasks that simply run once.
- Allows entering multiple lines of commands to be executed.
Key Options
Learn various ways to schedule and manage tasks using the `at` command.
1. Basic Usage and Job Scheduling
2. Job Management
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Frequently Used Examples
Learn how to use the command through real-world scenarios utilizing `at`.
Shutdown system at a specific time
at 10:30 PM
> sudo shutdown -h now
> (Ctrl+D)Schedules the system to shut down at 10:30 PM.
Display a notification message after 1 hour
at now + 1 hour
> echo "It's lunchtime!"
> (Ctrl+D)Displays 'It's lunchtime!' message in the terminal 1 hour from the current time.
Execute script at 8 AM tomorrow
at 8:00 AM tomorrow
> /home/user/scripts/backup.sh
> (Ctrl+D)Executes the `backup.sh` script at 8 AM tomorrow. (It's safer to specify the script path as an absolute path.)
Check scheduled job list
at -lChecks all `at` jobs scheduled for the current user account.
Delete a specific scheduled job
at -r 1Deletes the job using the job number (e.g., `1`) confirmed with the `at -l` command.
at Installation (if needed)
`at` is pre-installed on most Linux distributions. However, if it's not installed, you need to install the `atd` (at daemon) package using the commands below.
Debian/Ubuntu
sudo apt update
sudo apt install atHow to install atd on Ubuntu or Debian-based systems.
CentOS/RHEL/Fedora
sudo yum install at
sudo systemctl enable atd
sudo systemctl start atdHow to install atd on CentOS, RHEL, or Fedora-based systems.