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kresd.systemd(7) Knot Resolver Systemd Units kresd.systemd(7)


kresd.systemd - managing Knot Resolver through systemd.




This manual page describes how to manage kresd using systemd units. Depending on your distribution, this can be either be done with socket-based activation or without it. The following assumes socket-based activation. For differences see NOTES below.

kresd daemon can be executed in multiple independent processes, which can be managed with systemd via systemd templates (see systemd.unit(5)). Each systemd service instance of kresd (kresd@.service) represents a single, independent kresd process.

The systemd-managed kresd service set is grouped in the system-kresd.slice slice. The slice includes one or more running daemons (instances of kresd@.service), public listening sockets (the same listening sockets are shared by all daemons) and a dedicated control socket for each running daemon.

Each instance of kresd@.service has three systemd sockets (see systemd.socket(5)) associated with it:

kresd.socket - UDP/TCP network socket (default: localhost:53), shared with other instances
kresd-tls.socket - network socket for DNS-over-TLS (default: localhost:853), shared with other instances
kresd-control@.socket - UNIX socket with control terminal, dedicated

Configuring network interfaces

When using socket-based activation, the daemon requires neither root privileges nor any special capabilities, because the sockets are created by systemd and passed to kresd. This means kresd can't bind to ports below 1024 when configured in /etc/knot-resolver/kresd.conf.

To configure kresd to listen on public interfaces, drop-in files (see systemd.unit(5)) should be used. These can be created with:

systemctl edit kresd.socket
systemctl edit kresd-tls.socket

For example, to configure kresd to listen on on ports 53 and 853, the drop-in files would look like:

# /etc/systemd/system/kresd.socket.d/override.conf
# /etc/systemd/system/kresd-tls.socket.d/override.conf

For more detailed socket configuration, see systemd.socket(5).

Concurrent daemons

If you have more than one CPU core available, a single running kresd daemon will only be able to make use of one core at a time, leaving the other cores idle. If you want kresd to take advantage of all available cores, while sharing both cache and public listening ports, you should enable and start as many instances of the kresd@.service as you have cores. Typically, each instance is just named kresd@N .service, where N is a decimal number. To enable 3 concurrent daemons:

systemctl enable --now kresd@1.service kresd@2.service kresd@3.service

Using system-kresd.slice and

The following commands may not work with older systemd (e.g. on CentOS 7). See notes for more info.

The easiest way to view the status of systemd-supervised kresd instances is to use the system-kresd.slice:

systemctl status system-kresd.slice

You can also use the slice to restart all sockets as well as daemons:

systemctl restart system-kresd.slice

Or you can use it to stop kresd altogether (e.g. during package removal):

systemctl stop system-kresd.slice

To start all enabled kresd daemons, use the provided

systemctl start


  • When an instance of kresd@.service is started, stopped or restarted, its associated control socket is also automatically started, stopped or restarted, but the public listening sockets remain open. As long as either of the public sockets are listening, at least kresd@1.service will be automatically activated when a request arrives.

  • If your distribution doesn't use socket-based activation, you can configure the network interfaces for kresd in /etc/knot-resolver/kresd.conf. The service can be started or enabled in the same way as in the examples below, but it doesn't have any sockets associated with it.

  • Controlling the service with system-kresd.slice requires newer systemd. It may not work in some distributions, notably CentOS 7. To control multiple kresd instances, use kresd@*.service or Brace Expansion mentioned below.


Single instance

To start the service:

systemctl start kresd@1.service

To start the service at boot:

systemctl enable kresd@1.service

To delay the service startup until some traffic arrives, start (or enable) just the sockets:

systemctl start kresd.socket
systemctl start kresd-tls.socket

To disable the TLS socket, you can mask it:

systemctl mask kresd-tls.socket

Multiple instances

Multiple instances can be handled with the use of Brace Expansion (see bash(1)).

To enable multiple concurrent daemons, for example 16:

systemctl enable kresd@{1..16}.service

To start all enabled daemons:

systemctl start


kresd(8), systemd.unit(5), systemd.socket(5),


kresd developers are mentioned in the AUTHORS file in the distribution.
2018-06-04 CZ.NIC