# Back up and restore

The configuration database is the only state worth keeping. `nxdns export`
writes it out as a ZON file and `nxdns import` writes one back. The query log is
deliberately not part of a backup: it is expendable history, and if it is
missing it gets recreated empty.

The commands below use the scratch lab from
[enable DoH and DoT](enable-doh-and-dot.md), data directory
`/tmp/nxdns-lab/data`. On a real install drop `--data-dir` and the default
`/var/lib/nxdns` applies.

## Back up

One command, against a stopped or a running server:

```sh
nxdns export --data-dir /tmp/nxdns-lab/data --out /tmp/nxdns-lab/backup.zon
```

```
wrote /tmp/nxdns-lab/backup.zon
```

The write is a temp file plus a rename, so an interrupted export leaves no
half-written backup, and the result is mode 0600:

```sh
stat -c '%a %n' /tmp/nxdns-lab/backup.zon
```

```
600 /tmp/nxdns-lab/backup.zon
```

That mode is not decoration. The file carries `web.password_hash`:

```sh
grep password /tmp/nxdns-lab/backup.zon
```

```
        .password = "",
        .password_hash = "$argon2id$v=19$m=19456,t=2,p=1$Gh+zg9xke6BqSVOiouRbqG50+Bs8ZGcXA6oKgs7lrKg$crTNMu5OI8yKBkp31r4+Y1OUQmLiAlH/qvsIxjBQRq4",
```

Treat backups as secrets. `.password` is always exported as `""` — the
plaintext is never stored anywhere — so the file re-imports without anyone
knowing the password.

Without `--out` the export goes to stdout, where the file mode is your
redirect's problem:

```sh
nxdns export --data-dir /tmp/nxdns-lab/data | head -6
```

```
// nxdns configuration
// generated by `nxdns export` — the database is the source of truth
.{
    .upstream = .{ .read_timeout_ms = 3000, .total_timeout_ms = 5000 },
    .dns = .{
        .bind_ipv4 = "127.0.0.1",
```

Runtime facts are left out on purpose: client first-seen and last-seen times,
rule creation times, per-source domain counts and checksums. They are things a
running server produces, not configuration, and including them would make two
exports taken minutes apart differ.

## Restore onto a fresh data directory

This is the normal restore: new machine, new disk, empty data directory. No
`--force`, because there is nothing to overwrite.

```sh
nxdns import /tmp/nxdns-lab/backup.zon --data-dir /tmp/nxdns-lab/data-restored
```

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

The migration line is expected: `import` creates and migrates the database
before writing to it.

## Restore over an existing database

`import` refuses a database that already holds configuration, so a plain
`import` can never clobber a configured server by accident:

```sh
nxdns import /tmp/nxdns-lab/backup.zon --data-dir /tmp/nxdns-lab/data
```

```
import failed: DatabaseNotEmpty
```

That exits 2. Say `--force` when replacing is what you mean:

```sh
nxdns import /tmp/nxdns-lab/backup.zon --force --data-dir /tmp/nxdns-lab/data
```

```
imported /tmp/nxdns-lab/backup.zon
```

Stop the server first. `import` replaces the whole configuration underneath a
process that has already read it, and a running server will not notice.

What `--force` does to the client list is worth knowing before you restore an
old backup. A client the backup does not name is removed, and its first-seen
and last-seen go with it — restoring a month-old file drops the devices you
named since. Devices the server discovered from traffic are kept, and a device
the backup does name keeps the first-seen and last-seen the database already
held, so a restore does not restamp your whole network as newly arrived.

On a real install that is the systemd unit:

```sh
systemctl stop nxdns
nxdns import /var/backups/nxdns-config.zon --force
systemctl start nxdns
```

**Not verified on this host.** Those three lines are the only commands on this
page that were not run: this machine has no installed nxdns systemd unit
(`systemctl status nxdns` answers `Unit nxdns.service could not be found.`) and
`systemctl stop`/`start` need root. The lab equivalent below was run, and it
exercises the same stop-import-start sequence. In the lab the server is a
foreground `nxdns run`, so stopping it is Ctrl-C in its own terminal:

```sh
nxdns export --data-dir /tmp/nxdns-lab/data --out /tmp/nxdns-lab/pre-restore.zon
# Ctrl-C the `nxdns run` terminal, or `kill` its pid from another shell
nxdns import /tmp/nxdns-lab/pre-restore.zon --force --data-dir /tmp/nxdns-lab/data
nxdns run --data-dir /tmp/nxdns-lab/data --config /tmp/nxdns-lab/etc/config.zon
```

```
wrote /tmp/nxdns-lab/pre-restore.zon
imported /tmp/nxdns-lab/pre-restore.zon
```

## Verify a backup

The round trip is byte-stable: exporting, importing and exporting again gives
an identical file. That is the cheapest check that a backup is complete and
that it will load.

```sh
nxdns export --data-dir /tmp/nxdns-lab/data --out /tmp/nxdns-lab/backup2.zon
diff /tmp/nxdns-lab/backup.zon /tmp/nxdns-lab/backup2.zon \
  && echo "round trip is byte-identical"
```

```
wrote /tmp/nxdns-lab/backup2.zon
round trip is byte-identical
```

The same check works across data directories — export from the restored copy
and diff against the backup you restored from:

```sh
nxdns export --data-dir /tmp/nxdns-lab/data-restored --out /tmp/nxdns-lab/backup3.zon
diff /tmp/nxdns-lab/backup.zon /tmp/nxdns-lab/backup3.zon \
  && echo "restored database exports identically"
```

```
wrote /tmp/nxdns-lab/backup3.zon
restored database exports identically
```

## What is not in the backup

Everything under the data directory other than `config.db`:

- `querylog.db` — expendable history, recreated empty when absent.
- `blocklists/` — compiled snapshots. They are rebuilt from the sources named in
  the configuration, so restoring the configuration is enough; the first refresh
  after a restore downloads them again.

The data directory layout is in
[files and directories](../reference/files-and-directories.md).

## A backup before every upgrade

There is no downgrade path. Schema migrations run forward automatically at
startup and before `export` and `import`; nothing walks them back, and `nxdns
check` does not run them at all. Take an export before installing a new binary —
see [upgrade](upgrade.md).

Every command on this page was executed on this host as written, except the
`systemctl` block marked **Not verified on this host** above.
