I don't know if this additional information will help some more, but I installed this particular OS very shortly after release, then shelved it for several months until today, when I decided it would be useful for something I need.
I then did the usual "sudo apt update; sudo apt upgrade" command to ensure the system was up to date, before trying to "sudo apt install libncurses-dev". - Trey NOTICE TO RECIPIENT: This email, including attachments, may contain information which is confidential, proprietary, attorney-client privileged and / or controlled under U.S. export laws and regulations and may be restricted from disclosure by applicable State and Federal law. Nothing in this email shall create any legal binding agreement between the parties unless expressly stated herein and provided by an authorized representative of Comtech Telecommunications Corp. or its subsidiaries. If you are not the intended recipient of this message, be advised that any dissemination, distribution, or use of the contents of this message is strictly prohibited. If you received this message in error, please notify us immediately by return email and permanently delete all copies of the original email and any attached documentation from any computer or other media.
