kresd.systemd man page

kresd.systemd — managing Knot DNS Resolver through systemd.

Synopsis

kresd@.service
kresd.socket
kresd-tls.socket
kresd-control@.socket
kresd.target
system-kresd.slice

Description

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 192.0.2.115 on ports 53 and 853, the drop-in files would look like:

  # /etc/systemd/system/kresd.socket.d/override.conf
  [Socket]
  ListenDatagram=192.0.2.115:53
  ListenStream=192.0.2.115:53

# /etc/systemd/system/kresd-tls.socket.d/override.conf
[Socket]
ListenStream=192.0.2.115:853

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 kresd.target

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 kresd.target:

  systemctl start kresd.target

Notes

Examples

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.target

See Also

kresd(8), systemd.unit(5), systemd.socket(5), https://knot-resolver.readthedocs.io

Authors

kresd developers are mentioned in the AUTHORS file in the distribution.

Referenced By

kresd(8).

2018-06-04 CZ.NIC Knot DNS Resolver Systemd Units