Symptoms
queueprocd is unable to start with error
The “NOTIFY_SOCKET” environment variable is empty. at /usr/local/cpanel/Cpanel/Systemd/Notify.pm line 424.
Description
This has been found to be caused by an incorrectly set Type for systemd configuration for queueprocd.
Workaround
Modify /etc/systemd/system/queueprocd.service and change
Type=forking
to instead be
Type=notify
Then run
systemctl daemon-reload
/scripts/restartsrv_queueprocd