happy blog: systemd-networkd

This is happy blog post or at least not so negative, so this
closes #56.

_posts/2015-05-27-systemd-networkd.md

@@ -0,0 +1,93 @@
+---
+layout: post
+comments: true
+title: "My systemd-networkd setup"
+category: [english]
+tags: [english, systemd-networkd]
+---
+
+*This is happy post so probably useless, but my blog is always so
+unhappy… Anyway, systemd-networkd on my hosts.*
+
+I am running systemd-networkd on wired hosts as I am not so sure how it
+works with wireless hosts and I am using network manager with WLAN
+connections.
+
+The hosts mentioned here are
+* Zaldaryn which runs Ubuntu MATE 15.04
+* Rbtpzn which currently runs Antergos and is the oldest PC I have and
+  it's also the first one ever where I installed Ubuntu 8.04 in 2008.
+
+First you create network connection, I call them with the adapter name,
+e.g. Rbtpzn has `/etc/systemd/network/enp0s18.network` and Zaldaryn
+`/etc/systemd/network/eth0.network`.
+
+It appears that I have been experimenting with the two hosts, so the
+files differ. Here is Zaldaryn which looks more proper or direct copy
+from Arch Wiki:
+
+```
+[Match]
+Name=eth0
+
+[Network]
+DNS=127.0.0.1
+
+[Address]
+Address=172.16.1.6
+
+[Route]
+Gateway=172.16.0.1
+```
+
+and Rbtpzn
+
+```
+[Match]
+Name=enp0s18
+
+[Network]
+Address=172.16.1.2/16
+Gateway=172.16.0.1
+# DNS has no effect unless systemd-resolved is used
+# systemctl enable systemd-resolved && systemctl start systemd-resolved
+# ln -sf /run/systemd/resolve/resolv.conf /etc/resolv.conf
+DNS=127.0.0.1
+DNS=::1
+DNS=8.8.4.4
+NTP=pool.ntp.org
+```
+
+As you can see, they are quite different, Zaldaryn has everything neatly
+separated and Rbtpzn has everything in the same block.
+
+Match specifies which network interface is in question, Address is IP
+address of the host. I am not sure where I took NTP and as the Rbtpzn block
+says, you must use systemd-resolved for the DNS settings to do anything,
+but that is easy, just run as root (or prefix all three commands
+with `sudo`):
+
+```
+systemctl enable systemd-resolved && systemctl start systemd-resolved
+ln -sf /run/systemd/resolve/resolv.conf /etc/resolv.conf
+```
+
+The address can also have CIDR specified which probably should be done, but
+it appears that systemd-networkd can guess it correctly as everything works
+with Zaldaryn which doesn't have it specified.
+
+I am also using `systemd-networkd-wait-online.service`
+(`systemctl enable systemd-networkd-wait-online.service`) so
+`network.target` means that I have IP address before boot continues. There
+is 90 second timeout, but I still don't feel like trying this with wireless
+host as I would have 90 seconds longer boot time in new environments.
+
+Currently the only thing using network.target for me is Reflector service
+from Archwiki which updates mirrorlist with the fastest last synced mirrors
+on boot on Rbtpzn.
+
+Sources/further reading
+* https://wiki.archlinux.org/index.php/Systemd-networkd
+* http://www.freedesktop.org/software/systemd/man/systemd.network.html
+* https://wiki.freedesktop.org/www/Software/systemd/NetworkTarget/
+* https://wiki.archlinux.org/index.php/Reflector#Systemd_Service