New: systemd networking and timer notes

notes/linux/systemd_networkd.md

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+# Systemd-networkd
+Systemd's networking is effectively composed of 3 parts. The interface configs
+in `systemd-networkd`, the DNS resolver? in `systemd-resolved` and the wireless
+interface, for our purposes `iwd`
+
+`iwd` is only necessary for wifi
+
+ - `/etc/iwd/main.conf`: Disabling passive scanning
+ - `/var/lib/iwd/`: Per-network profiles, notably for WEP-Enterprise
+ - `/etc/iwd/main.conf`: Daemon settings
+ - `/etc/systemd/network`: For networkd stuff, so links and addresses
+ - `/etc/systemd/system/systemd-networkd-wait-online.service.d`
+ - `/etc/systemd/resolved.conf`: For resolved
+ - `/etc/nsswitch.conf`: For nss-mdns
+ - `/etc/mdns.allow`: Also for nss-mdns, only when not using mdns_minimal

notes/linux/systemd_timers.md

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+# Systemd Timers
+Gen Z's crontab
+
+Generally there are 3 pieces to a timer
+ - The script being run
+ - The systemd service defining which script to run
+ - The systemd timer triggering the service
+
+## Tools
+`systemd-analyze calendar` can be very handy at verifying timestamps
+
+```bash
+systemd-analyze calendar *-*-* *:10,20:10
+```
+
+To find suitable targets for things like `Wants` and `After`, see
+`systemd.special(7)`. If you want to check the current status of your targets,
+use:
+
+```bash
+systemctl list-units --type target --state active
+systemctl status network-online.target
+```
+
+## Placing files
+
+Scripts should be put in `/usr/local/bin` if they can be run by anyone or
+`/usr/local/sbin` if they should only be run by root
+
+Define a `xxx.service` file in `/etc/systemd/system`. Set the timer as one of
+its `Wants`. `network.target` may be more appropriate in some cases.
+`multi-user.target` is a good default for `WantedBy`
+
+```systemd
+[Unit]
+Description = Sends current ip address to uni servers
+Wants = broadcast_ip.timer
+Wants = network.target
+After = network.target
+
+[Service]
+Type = oneshot
+ExecStart = /usr/local/bin/broadcast_ip.sh
+
+[Install]
+WantedBy = multi-user.target
+```
+
+Now you'll need a timer file. It's easiest to make it have the same name as the
+service file and put it in the same `/etc/systemd/system`
+
+```systemd
+[Unit]
+Description = Sends current ip address to uni servers
+Requires = broadcast_ip.service
+
+[Timer]
+Unit = broadcast_ip.service
+OnCalendar = *-*-* *:15,45:00
+
+[Install]
+WantedBy = timers.target
+```