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.

For what each flag does, see the CLI reference; for what each configuration field means, see the configuration reference.

Verification: the build steps and systemd-analyze verify were run on the machine that wrote this page. nxdns check 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.

1. Build the binary

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

(cd web && npm ci && npm run build)
zig build cross -Dweb-dist=web/dist -Doptimize=ReleaseSafe

The first command builds the admin interface into web/dist; the second 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.

Two static musl binaries come out, one per deploy target:

• zig-out/cross/x86_64-linux-musl/nxdns
• zig-out/cross/aarch64-linux-musl/nxdns

Both are statically linked and need nothing installed on the target host.

2. Copy the files to the target

scp zig-out/cross/x86_64-linux-musl/nxdns target:/tmp/nxdns
scp deploy/systemd/nxdns.service deploy/systemd/sysusers.conf target:/tmp/

For a Raspberry Pi 5, copy zig-out/cross/aarch64-linux-musl/nxdns instead — see 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. What was verified is that both source paths exist after step 1 and that the aarch64 file is a statically linked aarch64 ELF executable.

Before copying, you can confirm the unit file parses:

systemd-analyze verify deploy/systemd/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.

3. Install the binary, the user and the unit

Run as root on the target:

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

install -m 0644 /tmp/sysusers.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

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 seed configuration

nxdns starts from an empty database only if a configuration file tells it what to forward to. Write /etc/nxdns/config.zon. The smallest file that starts is one group named default and one enabled upstream:

.{
    .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:

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:

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 https://cloudflare-dns.com/dns-query
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.

The file seeds the database once. From the second start onwards it is ignored and the database is the configuration; see the configuration model and Upgrade nxdns for how to change settings after that.

Once the seed has been consumed — after step 6 confirms you can log in — the plaintext in it is dead weight that only carries risk. The seed's web.password is hashed into web.password_hash at import time and the plaintext is never stored; nxdns export writes .password = "" back out alongside the hash. Nothing downstream ever reads the plaintext again, so delete the file:

rm /etc/nxdns/config.zon

Keep it only if you want the seed as a record of the intended starting configuration, and if you keep it, leave it at 0640 root:nxdns. Note that a kept seed is not a backup — nxdns export is (see Back up and restore), and the export carries the password hash rather than the password.

Verified on this host, with a scratch --config and --data-dir in place of /etc/nxdns and /var/lib/nxdns: a seed written under umask 022 came out 0644, nxdns check --config on it printed OK: no problems found with no mode warning, and after nxdns import of that seed an nxdns export wrote .password = "" next to a populated .password_hash = "$argon2id$v=19$...". The chown, chmod and rm lines above are the ordinary root-owned-file operations and were not run against a real /etc/nxdns, which this host does not have.

5. Start it

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 0.1.0-dev 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.

If the start fails, read Troubleshoot nxdns. The two common first-install failures are a port 53 already held by systemd-resolved and a seed file that does not parse.

6. Confirm it answers

From another machine on the LAN:

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

The admin interface is on port 8080 by default; log in with the password from the seed 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.

Raspberry Pi 5

The Pi 5 is aarch64. Nothing about the procedure changes except which binary you copy — the cross build needs no toolchain on the Pi and no toolchain beyond Zig on the build machine:

(cd web && npm ci && npm run build)
zig build cross -Dweb-dist=web/dist -Doptimize=ReleaseSafe
scp zig-out/cross/aarch64-linux-musl/nxdns pi:/tmp/nxdns
scp deploy/systemd/nxdns.service deploy/systemd/sysusers.conf pi:/tmp/

Then follow steps 3 to 6 on the Pi.

The build was run on the machine that wrote this page and zig-out/cross/aarch64-linux-musl/nxdns is a statically linked aarch64 ELF executable.

Not verified on this host: the two scp lines. pi is a placeholder for your Pi's hostname, and this page was written on an x86_64 machine with no Pi attached. The build steps above it were run; the copy was not.

Not verified on this host: the aarch64 binary was not executed. This host is x86_64 and has no qemu-aarch64 to run it under. Running it needs a Raspberry Pi 5 or another aarch64 machine.