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98162ea989
fergal is an 8-port SFP+ switch on a Realtek RTL9303, running OpenWrt rather than RouterOS or UniFi. It is not part of the fabric yet, but its firmware is now built here via astro's nix-openwrt-imagebuilder. Packages are baked into the image: OpenWrt's package server keeps only the current build of each feed, so installing at runtime stops working as soon as the feed moves past the running firmware. Those feed indexes rotate constantly, and upstream pins only the indexes -- a mismatch drops evaluation into import-from-derivation, putting this flake's eval on the network. The openwrt-feeds input pins expanded per-package hashes instead, in a repository of its own because they run to hundreds of thousands of generated lines. Flashing gets a procedure doc and a thin skill pointing at it, the same split as the box installation and nixpkgs upgrade procedures. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
104 lines
4.4 KiB
Markdown
104 lines
4.4 KiB
Markdown
# Flashing an OpenWrt box
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Guided procedure for putting a flake-built OpenWrt image onto a box. The images themselves are
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declared in [`openwrt/default.nix`](../openwrt/default.nix) and described in
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[`deployment.md`](deployment.md#openwrt-images); the boxes are listed on their site pages (today
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that is [fergal](sites/home/switches.md#fergal-the-openwrt-switch)).
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Packages are baked into the image, so this runs whenever the package list changes — not only for
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version upgrades. Work through the phases in order; ⏸ marks the point to stop and confirm.
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## Phase 1 — Build
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```sh
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nix build .#openwrt-<box>
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```
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The result holds the `-squashfs-sysupgrade.bin` to flash, plus a `.manifest` listing every package
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in the image and an SBOM. Check the manifest for the packages the change was meant to add — an
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unknown package name is not an error at build time, it just silently isn't there.
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## Phase 2 — Pre-flight
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Confirm on the box:
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```sh
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grep -E 'RELEASE|REVISION' /etc/openwrt_release # what is running now
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mount | grep -E ' / | /overlay | /rom ' # flash or RAM? (see below)
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uci get network.lan.ipaddr # will it come back reachable?
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cat /lib/upgrade/keep.d/* # what survives the flash
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df -h /tmp # room for the image
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```
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**Flash or RAM matters.** A box booted normally shows a squashfs `/rom` plus a jffs2 `/overlay`;
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one booted from an initramfs has `/` on tmpfs. The initramfs case has its own hazards — see
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[Flashing from an initramfs](sites/home/switches.md#flashing-notes).
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**Check the address is in UCI**, not just present on the interface. An address added by hand with
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`ip` disappears on reboot and the box comes back unreachable.
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`keep.d` normally lists `/etc/config/`, `/etc/dropbear/authorized_keys` and the dropbear host keys,
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so an ordinary flash preserves both access and identity. Verify rather than assume — losing
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`authorized_keys` on a box reachable only over SSH means a serial console recovery.
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## Phase 3 — Back up
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```sh
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sysupgrade -b /tmp/<box>-config-backup.tar.gz
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```
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Fetch it with `ssh <box> 'cat /tmp/…' > local.tar.gz`. **`scp` does not work** — these boxes have no
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`/usr/libexec/sftp-server`, so it fails with `Connection closed`. (`scp -O` forces the legacy
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protocol if you prefer it.)
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For a box being flashed off its **vendor** firmware for the first time, back up the whole flash
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first — the vendor partitions hold per-unit MAC addresses and licence data that cannot be
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regenerated. See [fergal's flash layout](sites/home/switches.md#flash-layout).
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## Phase 4 — Stage and validate
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```sh
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ssh <box> 'cat > /tmp/sysupgrade.bin' < <image>.bin
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ssh <box> 'sha256sum /tmp/sysupgrade.bin; sysupgrade -T /tmp/sysupgrade.bin'
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```
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Compare the sha256 against the local file, and require `sysupgrade -T` to exit 0. `-T` validates the
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image and its device-compatibility metadata without writing anything, which is the last cheap chance
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to catch a wrong-profile image.
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## Phase 5 — Flash ⏸
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Confirm before this point. It reboots the box and is not interruptible.
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```sh
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ssh <box> 'setsid sh -c "sleep 2; sysupgrade -v /tmp/sysupgrade.bin" \
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</dev/null >/tmp/upgrade.log 2>&1 & echo detached'
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```
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**Detaching matters.** `sysupgrade` kills the SSH session partway through; without `setsid` the
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upgrade dies with it, potentially after the flash has been erased. `nohup` is not available on these
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boxes' busybox — use `setsid`.
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Plain `sysupgrade` keeps the config in `keep.d`. Do not reach for `-c` out of caution: it needs
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`/overlay/upper/etc` and aborts *after* erasing the firmware if that is missing.
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## Phase 6 — Wait and verify
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Poll SSH, not ping. A successful ping returns in milliseconds, so a naive "wait for it to go down"
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loop finishes before the box has even started rebooting. Sleep between probes and wait on something
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that only succeeds once userspace is up:
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```sh
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for i in $(seq 1 40); do
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sleep 15
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ssh -o ConnectTimeout=5 -o BatchMode=yes <box> 'grep REVISION /etc/openwrt_release' && break
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done
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```
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Expect roughly three minutes. Then confirm the revision changed, the management address returned,
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the package count matches the manifest, and the new packages are actually present and running.
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Connecting without host-key overrides also confirms the host keys survived.
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If the box does not return, it needs the serial console — have that confirmed as reachable *before*
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Phase 5, not after.
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