rolfie wrote:

The main repo is missing.

http://deb.devuan.org/merged beowulf main contrib non-free 

Consider if you need to complie packages. If not, disable the deb-src lines.

What does non-free mean in this context? Licenses other than GPL, MIT, and their kin?

cat /etc/apt/sources.list
# 

# deb cdrom:[Devuan GNU/Linux 3.0 (beowulf) amd64 - desktop 20200526]/ beowulf contrib main non-free

# deb cdrom:[Devuan GNU/Linux 3.0 (beowulf) amd64 - desktop 20200526]/ beowulf contrib main non-free

# A network mirror was not selected during install.  The following entries
# are provided as examples, but you should amend them as appropriate
# for your mirror of choice.
#
deb http://deb.devuan.org/merged beowulf-security main
deb-src http://deb.devuan.org/merged beowulf-security main

# beowulf-updates, previously known as 'volatile'
# A network mirror was not selected during install.  The following entries
# are provided as examples, but you should amend them as appropriate
# for your mirror of choice.
#
deb http://deb.devuan.org/merged beowulf-updates main
deb-src http://deb.devuan.org/merged beowulf-updates main

1. Got any other sources I should use (mirrors, for instance), and if so can you tell me why (or point me towards something that will tell me what and why)?

2. Got anything to read RE mirrors and how that helps me or Devuan in general?

During the upgrade (which was blessedly fast and simple compared to Windows 10), I noticed this:

/etc/kernel/postinst.d/initramfs-tools:
update-initramfs: Generating /boot/initrd.img-4.19.0-9-amd64
W: Possible missing firmware /lib/firmware/tigon/tg3_tso5.bin for module tg3
W: Possible missing firmware /lib/firmware/tigon/tg3_tso.bin for module tg3
W: Possible missing firmware /lib/firmware/tigon/tg3.bin for module tg3

A search indicates it could prevent network cards from working after reboot. If that's an issue, the same says that I need to add non-free to my sources.
https://thespecter.net/blog/technology/ … odule-tg3/

Going back to the link rolfie posted:

Note that all software shipped with Devuan in the main component is free software. But if needed, non-free software is also available. Just add the non-free and contrib components to the appropriate line(s) in /etc/apt/sources.list like this:

deb http://deb.devuan.org/merged beowulf main non-free contrib

Is there any way to specify that I only want certain software from a specific source? I do a lot of emulation and rom-hacking stuff, and the authors of programs for such love to require the latest stable versions for compilation.

How would I add package sources from debian while restricting it to the subsets that don't require things that are forbidden in devuan?

Where can I see the list of packages that are forbidden?