The Patient List Viewer invokes the at commands to place jobs in the background. This frees up the UI while long queries are running.
Some Linux systems do not have the at command installed.
The ATD service is installed along with the at command. This service is required to be running for the at command to work
Install at by using your packaged manager. For example, if you are using yum as a package manager, type in:
# yum install at
To start the ATD services on newer systems, type in:
# systemctl start atd
For older systems type in:
# /etc/init.d/atd start