[SOLVED] Upgraded Stretch->Buster, lost network. How to set up simple DHCP connection?

Standalone desktop, initial installation was a long time ago (Wheezy or Jessie), and I've been upgrading with apt since then, without problems. After upgrading to Buster, some programs broke due to missing libraries - and worst of all, there was no network up, on reboot.

I had been using a cable modem, with dhcp - nothing fancy. It had always "worked" so I didn't look into how it was working. Now, I'm completely lost as to the best way to set it up.

Manually running "ifconfig eth0 up" and "dhclient eth0" after every reboot does work, and Internet connectivity seems fine with them.

BUT - what is the best way to set up an automatic, basic dhcp Internet connection? Searching yields a confusing, conflicting set of programs that could be involved:

1) network-manager
2) dhcpcd
3) resolvconf
4) sysctl
5) init.d/networking
6) ifconfig
7) isc-dhcp-client
8) systemd
9) various conflicting config files...

I have no idea how systemd impacts all this, and the systemd documentation might as well be hieroglyphics - it's completely bewildering. I can't make any sense of it.

Is there any simple guide to choosing which to use for a non-sysadmin user? Which of the above would be used by default with a fresh installation (I'd rather not go that route if I can avoid it)? The closest I've come is https://wiki.debian.org/NetworkConfiguration - but this just lists options without saying which to use and why.

You're usually best using what the distro uses. Personally I run slackware where you have the option of not using network manager, grub2, systems, or any of that [expletive deleted].

Resolved.conf is rewritten by just about everything as is the kernel routing table. Try

route

and see that you have your network device in there doing something. You can add or delete routes to get it there as default (man route). Then try your dhcpcd/dhclient eth0 or whatever your network device is. Post the errors.

Moving from stable to testing isn't an upgrade.

Easiest is just to define it in /etc/network/interfaces - pretty much every other tool reads/respects that.

i don't quite understand why you felt compelled to use testing instead of stable.
if this is the same install since wheezy, on the same machine, you very likely won't benefit from newer packages, rather the opposite.

if you installed wheezy first and steadily dist-upgraded, you went through the whole change from sysvinit to systemd. i have no idea if you have conflicting services now, and which of the 2 init systems has the lead or takes care of networking.
you have to hunt that down.

maybe, to make things easier, you could purge all high-level network applications - only networkmanager i guess - and get the basics working.
if you only use one wired internet connection, you don't really need networkmanager anyway.

maybe you also need to understand the difference between internet connection and name resolving.
try this:

ping 207.241.224.2
ping archive.org

if the first works, but the latter doesn't, means you have a name resolving (DNS) problem.

PS: imo archwiki has the best resources for understanding systemd: https://wiki.archlinux.org/index.php/Systemd

Originally Posted by ondoho i don't quite understand why you felt compelled to use testing instead of stable.

Thanks for your reply.

I had been using Stretch (and earlier releases) since it was testing, using apt to upgrade and dist-upgrade along the way - once Stretch became stable, I switched to Buster (or "testing").

What is the point of being able to dist-upgrade with apt if conflicts between releases aren't resolved? (that's not a challenge to your post, I am trying to understand it better)

you went through the whole change from sysvinit to systemd. i have no idea if you have conflicting services now, and which of the 2 init systems has the lead or takes care of networking. you have to hunt that down. maybe you also need to understand the difference between internet connection and name resolving.

Yes, I did upgrade along the way - the "hunting down" part is what I'm trying to figure out ;P What does a default, fresh install use to bring up the interface and start DHCP? I can't find that, specifically.

I understand the concepts of internet connections and DNS - the problem is I don't know which combination of programs to use to achieve them, which ones a default install uses, or what was being used before in Stretch.

I don't mind figuring it out by trial and error, but I'm trying to avoid installing something that creates an irresolvable conflict, or trashes systemd, etc., and then being forced to do a total reinstall.

I did read through the Arch Wiki on systemd, thanks.

Originally Posted by business_kid You're usually best using what the distro uses. Personally I run slackware where you have the option of not using network manager, grub2, systems, or any of that [expletive deleted].

Thanks for your reply!

I'm trying to use what the distro uses - but that's the problem ;P I can't figure out what the default is, or what is being used in testing that wasn't being used in Stretch.

I can connect, by manually using ifconfig and dhclient which works fine, but I don't know what I should be using to set that up automatically, or whether there are any conflicts to be aware of or how systemd plays into all of this.

I have run Slackware before, and I definitely like the minimalist/traditional focus.

Originally Posted by pepperslq What does a default, fresh install use to bring up the interface and start DHCP? I can't find that, specifically.

for a wired connection - systemd-networkd.

Originally Posted by pepperslq I can connect, by manually using ifconfig and dhclient which works fine, but I don't know what I should be using to set that up automatically

for a wired connection - systemd-networkd.

https://wiki.archlinux.org/index.php/Systemd-networkd
https://wiki.debian.org/systemd

Originally Posted by ondoho for a wired connection - systemd-networkd. https://wiki.archlinux.org/index.php/Systemd-networkd

Thanks ondoho!

I went the systemd route, and it seems to be working OK.

For anyone with the same problem, this is what I did:

1) create a config file in /etc/systemd/network, as shown in the archlinux wiki page above
2) systemctl enable systemd-resolved.service
3) systemctl enable systemd-networkd.service