nxdns/docs/how-to/install-with-systemd.md

# Install nxdns with systemd

Installs nxdns as a system service on a Linux host with systemd, including a
Raspberry Pi 5. At the end the service answers DNS on port 53 and starts on
boot.

The normal path is to download a released tarball, verify it, and install what
is inside it. Building from source is still supported and is the last section
of this page.

For what each flag does, see [the CLI reference](../reference/cli.md); for what
each configuration field means, see
[the configuration reference](../reference/configuration.md).

> Verification: `systemd-analyze verify` was run on the machine that wrote this
> page. `nxdns check`, `nxdns import`, `nxdns export` and `nxdns run` were run
> there too, but against a scratch `--data-dir` and `--config` on an
> unprivileged port, because that machine is not a deploy target and has no
> `/etc/nxdns`, no `/var/lib/nxdns` and no root. The steps that need root on a
> target host — `install`, `systemd-sysusers`, `systemctl` — were not run; they
> are marked where they appear.
>
> The download in step 1 could not be run at all: this repository has no tags
> and no published release, so every release URL on this page is a 404 today.
> Its commands are the ones [Verify a release](verify-a-release.md) covers in
> full, and the URL shapes — including the `releases/latest` redirect the
> version is read from — were probed there against `gitea.com`, a public
> instance running the same Gitea series.
>
> The `zig build dist` and `zig build verify-dist` blocks in the last section
> were run here, both to completion and both exiting 0; that section carries
> the detail.

## 1. Download and verify

Two static musl tarballs are published per release, one per architecture. Pick
`x86_64-linux-musl` for a normal PC or server and `aarch64-linux-musl` for a
Raspberry Pi 5.

```sh
BASE=https://git.mial.net/mokhtar/nxdns
VERSION=$(curl -fsS -o /dev/null -w '%{redirect_url}' "$BASE/releases/latest" |
  sed 's#.*/releases/tag/v##')
mkdir -p ~/nxdns-release && cd ~/nxdns-release
curl -fLO "$BASE/releases/download/v$VERSION/nxdns-$VERSION-x86_64-linux-musl.tar.gz"
curl -fLO "$BASE/releases/download/v$VERSION/SHA256SUMS.txt"
curl -fLO "$BASE/releases/download/v$VERSION/SHA256SUMS.txt.asc"
```

The first line asks the server which release is current instead of hardcoding a
number that goes stale one release later — Gitea redirects `releases/latest` to
the newest published release's tag page. To install a particular version
instead, set `VERSION=<version>` yourself with the one you want; the tarball
filenames carry the version either way, so there is no version-free download
URL for them.

Verify before you extract. The signature is over `SHA256SUMS.txt`, and
`SHA256SUMS.txt` is over the tarballs:

```sh
gpg --verify SHA256SUMS.txt.asc SHA256SUMS.txt
sha256sum -c --ignore-missing SHA256SUMS.txt
tar -xzf "nxdns-$VERSION-x86_64-linux-musl.tar.gz"
```

[Verify a release](verify-a-release.md) has the whole procedure: where the
public key comes from, what fingerprint to expect, what each failure means, and
what the signature does and does not prove. Read it once before your first
install.

The extracted directory `nxdns-$VERSION-x86_64-linux-musl/` holds everything
this page installs:

| File | What it is |
| --- | --- |
| `nxdns` | The static binary, mode 0755 |
| `nxdns.service` | The systemd unit |
| `nxdns.conf` | The sysusers fragment that creates the `nxdns` user |
| `LICENSE` | EUPL-1.2 |
| `THIRD-PARTY-NOTICES` | Licences of everything compiled or bundled in |
| `INSTALL.md` | A short version of this page |

> Not verified on this host: no release exists yet, so none of these commands
> could be run against one — the `releases/latest` lookup returns 404 for this
> repository and leaves `VERSION` empty. The same lookup was run against
> `gitea.com/gitea/tea` on Gitea `1.27.0+dev` and printed `0.15.1`.

## 2. Copy the files to the target

```sh
cd "nxdns-$VERSION-x86_64-linux-musl"
scp nxdns nxdns.service nxdns.conf target:/tmp/
```

For a Raspberry Pi 5, extract the `aarch64-linux-musl` tarball instead — see
[Raspberry Pi 5](#raspberry-pi-5) below.

> Not verified on this host: `target` is a placeholder for your server's
> hostname, and the machine that wrote this page has no second host to copy
> to.

Before copying, you can confirm the unit file parses:

```sh
systemd-analyze verify nxdns.service
```

Off the target host this prints one complaint and exits 1:

```
nxdns.service: Command /usr/local/bin/nxdns is not executable: No such file or directory
```

That is the ExecStart path check finding no binary yet. Any other message is a
real problem with the unit. On the target, after step 3, the same command
should print nothing.

> Verified on this host against `deploy/systemd/nxdns.service` in a checkout,
> which is the same file the tarball ships — the path is the only difference.

## 3. Install the binary, the user and the unit

Run as root on the target:

```sh
install -m 0755 /tmp/nxdns /usr/local/bin/nxdns

install -m 0644 /tmp/nxdns.conf /usr/lib/sysusers.d/nxdns.conf
systemd-sysusers

install -m 0644 /tmp/nxdns.service /etc/systemd/system/nxdns.service
systemctl daemon-reload

mkdir -p -m 0755 /etc/nxdns
```

The sysusers fragment ships under the name it is installed as, so there is no
rename to get wrong.

> Not verified on this host: these commands need root on a target machine. The
> files they install were read at HEAD and the unit was checked with
> `systemd-analyze verify`.

The service user is a static one, not `DynamicUser`: a TLS key for the DoH or
DoT listener has to be chown-able to a uid that survives a restart.

Do not create `/var/lib/nxdns` or `/var/log/nxdns` by hand. The unit's
`StateDirectory` and `LogsDirectory` settings make systemd create them on first
start, `/var/lib/nxdns` at mode 0700 owned by `nxdns`.

`/etc/nxdns` is the one directory the `mkdir` above is for. The unit's
`ConfigurationDirectory=nxdns` also creates it, but not until the first start
in step 5, and step 4 has to write a file into it before then. systemd does not
mind finding the directory already there; it adjusts the mode and ownership to
what the unit asks for.

## 4. Write the configuration

nxdns will not start with nothing to forward to. Write `/etc/nxdns/config.zon`.
The smallest file that starts is one group named `default` and one enabled
upstream:

```zon
.{
    .groups = .{ .{ .name = "default" } },
    .upstreams = .{ .{ .url = "https://cloudflare-dns.com/dns-query" } },
    .web = .{ .password = "choose-a-real-password" },
}
```

That file holds a password in plain text, so restrict it as soon as you have
written it:

```sh
chown root:nxdns /etc/nxdns/config.zon
chmod 0640 /etc/nxdns/config.zon
```

Root's umask is 022 on most distributions, so a freshly written
`/etc/nxdns/config.zon` is mode 0644 and every account on the host can read the
password out of it. The unit's `UMask=0077` does not help here: it applies to
files the service creates once it is running, and never re-chmods a file that
was written before the first start.

0640 with group `nxdns` rather than 0600: `/etc/nxdns` is a
`ConfigurationDirectory`, which systemd leaves owned by root, and the service
runs as `nxdns` and has to read this file on the first start. A root-owned 0600
file would be unreadable to it.

Do not expect `nxdns check` to catch a permissive mode here. Its only
permission warning is for a TLS private key
(`WARN doh_server.key_path: ... is mode 644; a TLS key must be readable by its
owner only`, from `checkTlsFiles` in `src/cli.zig`); it never stats the
configuration file. A mode 0644 `config.zon` passes `check` in silence, so the
`chmod` above is yours to remember.

Check it before you start the service:

```sh
nxdns check --config /etc/nxdns/config.zon
```

A good file prints the source it checked, one `OK` line per upstream, and
`OK: no problems found`:

```
checking configuration file /etc/nxdns/config.zon
OK upstreams[0] https://cloudflare-dns.com
OK: no problems found
```

The upstream probe sends a real query, so this needs working DNS on the host at
the time you run it. Exit 2 means `check` found something to fix and printed
every problem it found, not only the first.

Now load it into the database:

```sh
nxdns import /etc/nxdns/config.zon
```

```
info(migrations): config.db migrated from schema version 0 to 2
imported /etc/nxdns/config.zon
```

The plaintext password is hashed into `web.password_hash` and never stored as
plaintext; `nxdns export` writes `.password = null` beside the hash. Nothing
downstream reads the plaintext again, so once step 6 confirms you can log in you
can delete the file:

```sh
rm /etc/nxdns/config.zon
```

A kept file is not a backup — `nxdns export` is (see
[Back up and restore](back-up-and-restore.md)), and the export carries the
password hash rather than the password. If you keep it, leave it at 0640
root:nxdns.

That is the **database mode** install, which is what the packaged unit runs:
`ExecStart=/usr/local/bin/nxdns run`, no `--config`, so nothing reads a file
after this step. Change settings afterwards through the admin interface, the
API, or an export–edit–import cycle.

If you would rather keep `/etc/nxdns/config.zon` in git and have every restart
converge onto it, do not delete the file — go to
[Run in file mode](#run-in-file-mode) instead, and skip the `rm`.

> Verified on this host, with a scratch `--config` and `--data-dir` in place of
> `/etc/nxdns` and `/var/lib/nxdns` — those two paths are the only difference
> from the blocks above. A file written under umask 022 came out 0644,
> `nxdns check --config` on it printed `OK: no problems found` with no mode
> warning, `nxdns import` of it printed the migration line and `imported <path>`
> and exited 0, and a following `nxdns export` wrote `.password = null` next to
> a populated `.password_hash = "$argon2id$v=19$m=19456,t=2,p=1$…"`. The
> `chown`, `chmod` and `rm` lines are ordinary root-owned-file operations and
> were not run against a real `/etc/nxdns`, which this host does not have.

## 5. Start it

```sh
systemctl enable --now nxdns
journalctl -u nxdns -f
```

> Not verified on this host: needs root and an installed unit.

A healthy start logs a line naming every socket it bound:

```
info(nxdns): nxdns <version> serving on udp [::]:53 tcp [::]:53 tcp 0.0.0.0:53; 1 upstream(s); blocklist generation 1
```

nxdns writes to stderr and systemd captures that into the journal; logging
needs no further configuration. Port 53 is privileged, and the unit grants
`CAP_NET_BIND_SERVICE` through `AmbientCapabilities`.

The unit does not restart the service after exit 2 or exit 64
(`RestartPreventExitStatus=2 64`). Those are a wrong configuration and a wrong
command line, and neither clears on a retry — restarting every two seconds until
`StartLimitBurst` gives up would only bury the diagnostics that are already in
the journal. `systemctl status nxdns` shows the failed state; fix the cause and
start it again.

If the start fails, read [Troubleshoot nxdns](troubleshoot.md). The two common
first-install failures are a port 53 already held by `systemd-resolved` and a
configuration file that does not parse.

## 6. Confirm it answers

From another machine on the LAN:

```sh
dig @<server-ip> example.com A +short
```

The admin interface is on port 8080 by default; log in with the password from
the configuration file. `http://<server-ip>:8080/api/health` reports upstream
availability and disk state without a login.

> Not verified on this host as written: `<server-ip>` is a placeholder, and a
> LAN client to run it from is a second machine this host does not have. What
> was verified is the same two checks against a local nxdns started from a
> scratch data directory on an unprivileged port — `dig @127.0.0.1 -p 15353
> example.com A +short` returned the A records, and `curl` against the web
> port returned 200. Only the address and the port differ from the lines
> above.

## Run in file mode

In file mode `/etc/nxdns/config.zon` is the configuration: every start converges
the database onto it, and the admin interface refuses configuration edits with a
403 naming the file. Use it when you want the file in git and deployed by
Ansible. Stay in database mode when you want the UI to be the way things change.

The packaged unit is flagless on purpose — it is correct as shipped, and a
commented-out alternative `ExecStart` in a unit file is documentation
masquerading as configuration. File mode is a drop-in.

### Adopt file mode on a box that is already running

Run these in order. **Stop first**, and do not skip that: any edit made through
the UI between an export and the restart would be silently reverted by the first
reconcile, and `nxdns check` against a live database refuses to grade it (below).

If you are arriving here from an upgrade, the binary must already be the new
one before you export. An export written by 0.0.1 carries a `.password = ""`
line this binary refuses; see
[the order trap](upgrade.md#the-order-trap-export-with-the-new-binary-not-the-old-one).

```sh
systemctl stop nxdns
nxdns export --out /etc/nxdns/config.zon
nxdns check --config /etc/nxdns/config.zon
```

```
wrote /etc/nxdns/config.zon
checking configuration file /etc/nxdns/config.zon
OK upstreams[0] https://cloudflare-dns.com
OK: no problems found
```

Then add the drop-in and start:

```sh
mkdir -p /etc/systemd/system/nxdns.service.d
cat > /etc/systemd/system/nxdns.service.d/file-mode.conf <<'EOF'
[Service]
ExecStart=
ExecStart=/usr/local/bin/nxdns run --config=/etc/nxdns/config.zon
EOF
systemctl daemon-reload
systemctl start nxdns
```

The empty `ExecStart=` is required. Without it systemd appends a second command
to the list rather than replacing the first, and the unit tries to run nxdns
twice.

The first start after adoption changes nothing, because the file was rendered
from the database it is now governing:

```
reconciled '/etc/nxdns/config.zon': no changes
info(nxdns): authority: file (/etc/nxdns/config.zon)
info(nxdns): nxdns <version> serving on udp [::]:53 tcp [::]:53 tcp 0.0.0.0:53; 1 upstream(s); blocklist generation 1
```

`authority: file` is the line that confirms the drop-in took. Blocklists,
compiled snapshots and client history all survive, and every later start on an
unchanged file writes nothing either.

The file now carries `web.password_hash`, so restrict it the same way step 4
does — `chown root:nxdns`, `chmod 0640`. The unit's `ReadOnlyPaths=/etc/nxdns`
denies the service write access to that directory, so the process that reads the
file cannot modify it.

### Change the configuration from now on

Edit the file, validate it, restart:

```sh
$EDITOR /etc/nxdns/config.zon
nxdns check --config /etc/nxdns/config.zon
systemctl restart nxdns
```

Make `nxdns check --config` the precondition of any Ansible handler that
restarts nxdns. A file-mode start reads the file on **every** boot, so a bad
push that skips its handler does not fail at deploy time — it detonates at the
next power cut. Validating before restarting turns that into a failed deploy at
noon.

The restart prints what it changed:

```
reconciled '/etc/nxdns/config.zon': upstreams +1 ~0 -0; settings +0 ~2 -0;
settings keys changed: dns.port web.port
```

### Leave file mode

Remove the drop-in and restart. The database already holds the last reconciled
state, so nothing else is needed and the server comes back serving the same
configuration:

```sh
rm /etc/systemd/system/nxdns.service.d/file-mode.conf
systemctl daemon-reload
systemctl restart nxdns
```

```
info(nxdns): authority: database
```

> Verified on this host end to end, against a scratch `--data-dir` and a scratch
> configuration path instead of `/var/lib/nxdns` and `/etc/nxdns`, on
> unprivileged ports — this machine has neither of those directories, no root,
> and no installed unit. Every `nxdns` line above was run and produced the output
> shown, with only those paths and the port numbers in the `serving on` line
> differing.
>
> The run: a database-mode instance was started, a blocklist source was added
> through the API to make it UI-configured, then `nxdns check` against the live
> database printed the uncheckpointed-log FAIL and exited 2 (which is why this
> section stops the service first). After the stop, `nxdns export --out` wrote
> the file, `nxdns check --config` on it exited 0 with `OK: no problems found`,
> and the first file-mode start printed `reconciled '<path>': no changes` and
> `authority: file (<path>)`. A second file-mode start printed `no changes`
> again and loaded the 3096006-byte compiled blocklist from disk with no
> download. Dropping the flag printed `authority: database` and served the same
> configuration.
>
> The `systemctl`, `mkdir`, `cat > …/file-mode.conf` and `rm` lines need root and
> an installed unit and were **not** run. What was checked instead:
> `systemd-analyze verify` on `deploy/systemd/nxdns.service` with those exact two
> `ExecStart` lines appended, which reported only the usual
> `Command /usr/local/bin/nxdns is not executable` for the absent binary and
> nothing about the override.

## Raspberry Pi 5

The Pi 5 is aarch64. Nothing about the procedure changes except which tarball
you take:

```sh
curl -fLO "$BASE/releases/download/v$VERSION/nxdns-$VERSION-aarch64-linux-musl.tar.gz"
sha256sum -c --ignore-missing SHA256SUMS.txt
tar -xzf "nxdns-$VERSION-aarch64-linux-musl.tar.gz"
cd "nxdns-$VERSION-aarch64-linux-musl"
scp nxdns nxdns.service nxdns.conf pi:/tmp/
```

Then follow steps 3 to 6 on the Pi.

> Not verified on this host: no release exists to download, `pi` is a
> placeholder for your Pi's hostname, and this page was written on an x86_64
> machine with no Pi attached.

## Build from source instead

You do not need this to install nxdns, and it gets you a binary nobody has
signed. It is here for two cases: you want to run something other than a
tagged release, or you want to build the release yourself and compare it
against the published one. For the second case, follow
[Verify a release](verify-a-release.md) rather than this section — it says what
the comparison is and is not worth.

Requires Zig 0.16.0 and Node.js. From the repository root:

```sh
(cd web && npm ci && npm run build)
VERSION=$(sed -n 's/^[[:space:]]*\.version[[:space:]]*=[[:space:]]*"\([^"]*\)".*/\1/p' build.zig.zon)
zig build dist -Dversion-string="$VERSION" -Dgit-commit="$(git rev-parse HEAD)" \
    -Dweb-dist=web/dist -Doptimize=ReleaseSafe
```

The first command builds the admin interface into `web/dist`; the last one
embeds that directory in the binary. Build the interface every time, before the
binary: a stale `web/dist` ships an admin UI that does not match the API it
talks to. `dist` refuses to run against the `web/dist-placeholder` default for
exactly that reason, so there is no way to skip it by accident.

`-Dversion-string` is required and has no default. It is what `nxdns version`
prints. Take it from `build.zig.zon` rather than inventing one: `verify-dist`
asserts that the version under build equals `.version` there, so a made-up
string like `0.0.0-local` builds but then fails verification. `-Dgit-commit`
is what distinguishes your build from the published one of the same version.

What comes out under `zig-out/dist/` is the same set a release publishes,
minus the signature and the image digest:

- `bin/<triple>/nxdns` — the stripped static binary, one per target
- `stage/nxdns-<version>-<triple>/` — the staged payload, one per target
- `nxdns-<version>-<triple>.tar.gz` — one tarball per target
- `SHA256SUMS` — the two tarball hashes. The release publishes this as
  `SHA256SUMS.txt`, with a third line for the image digest appended

The two targets are `x86_64-linux-musl` and `aarch64-linux-musl`. Both binaries
are statically linked and need nothing installed on the target host.

Check the result the same way the release pipeline does:

```sh
zig build verify-dist -Dversion-string="$VERSION" -Dgit-commit="$(git rev-parse HEAD)" \
    -Dweb-dist=web/dist -Doptimize=ReleaseSafe
```

`verify-dist` extracts each archive and asserts the ELF is static and within
the size budget, that the layout and file modes are exactly what step 1 lists,
and that `nxdns version` prints what was built. It exits non-zero on any
failure.

> Verified on this host: `zig build dist` and `zig build verify-dist` were both
> run to completion with the version taken from `build.zig.zon`. `dist`
> produced the two tarballs, `SHA256SUMS` and the staged payloads described
> above; `verify-dist` exited 0 with every check passing and the aarch64
> `nxdns version` check skipped for want of `-fqemu`. Passing a made-up
> `-Dversion-string=0.0.0-local` was also run: `dist` succeeded and
> `verify-dist` then failed with
> `FAIL zon-version: build.zig.zon says '0.0.1', the build says '0.0.0-local'`,
> which is why this section reads the version out of `build.zig.zon`.

From here, join the page at step 2 with the staged directory in place of the
extracted one:

```sh
cd "zig-out/dist/stage/nxdns-$VERSION-x86_64-linux-musl"
scp nxdns nxdns.service nxdns.conf target:/tmp/
```

The aarch64 binary is built by the same command and needs no toolchain on the
Pi.