readme and install script

README.md

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+# steamos prometheus
+
+Heavily inspired by [Xe's guide to getting tailscale running](https://tailscale.com/blog/steam-deck/), this script installs prometheus' `node_exporter` onto a Steam Deck in a way that _should_ survive system updates.
+
+## Usage
+
+Make sure you have `sudo` access when in desktop mode by [setting a password for your `deck` user](https://gitlab.com/popsulfr/steam-deck-tricks#easy-ssh-access-to-the-steam-deck).
+
+Copy `./install.sh` onto your Deck, either over SSH or by copying it from a browser, then run `sudo bash ./install.sh`.
+
+If this is the first time you've installed a system extension, run `sudo systemd-sysext merge`.
+If you've already done something like the Tailscale install mentioned above, just `sudo systemd-sysext refresh`.
+
+To make sure that system extensions are loaded after reboot, run
+
+```sh
+sudo systemctl enable systemd-sysext
+sudo systemctl start systemd-sysext
+```
+
+Then you should be able to just
+
+```sh
+sudo systemctl enable prometheus-node-exporter
+sudo systemctl start prometheus-node-exporter
+```
+
+Installing a collector for the metrics now available on `:9100` is left as an exercise for the reader, but I figure if you're devoted to tracking system metrics enough to try and install prometheus on your Steam Deck you've probably already got a setup for that.
+
+## References
+
+* <https://tailscale.com/blog/steam-deck/>
+* <https://blogs.igalia.com/berto/2022/09/13/adding-software-to-the-steam-deck-with-systemd-sysext/>

install.sh

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+#!/usr/bin/env bash
+
+set -euo pipefail
+
+dir="$(mktemp -d)"
+pushd .
+cd "${dir}"
+
+BINARY=$(curl https://api.github.com/repos/prometheus/node_exporter/releases/latest | jq -r '.assets[] | select(.name | contains("linux-amd64")) | .browser_download_url')
+curl -L $BINARY -o node-exporter.tgz
+
+mkdir -p prometheus/usr/{bin,lib/{systemd/system,extension-release.d}}
+tar xzf node-exporter.tgz
+
+cp -vrf node_exporter-*/node_exporter prometheus/usr/bin/node_exporter
+cat > prometheus/usr/lib/systemd/system/prometheus-node-exporter.service <<- EOM
+[Unit]
+Description=Prometheus exporter for machine metrics
+Requires=network-online.target
+After=network-online.target
+
+[Service]
+Restart=on-failure
+ExecStart=/usr/bin/node_exporter
+ExecReload=/bin/kill -HUP \$MAINPID
+NoNewPrivileges=true
+ProtectHome=read-only
+ProtectSystem=strict
+
+[Install]
+WantedBy=multi-user.target
+EOM
+
+source /etc/os-release
+echo -e "SYSEXT_LEVEL=1.0\nID=steamos\nVERSION_ID=${VERSION_ID}" >> prometheus/usr/lib/extension-release.d/extension-release.prometheus-node-exporter
+
+mkdir -p /var/lib/extensions
+rm -rf /var/lib/extensions/prometheus-node-exporter
+cp -vrf prometheus /var/lib/extensions/prometheus-node-exporter
+
+popd
+rm -rf "${dir}"