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

NAME

kresd.systemd - managing Knot 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







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 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


    
  
  • 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.
    
    
  
    • 







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.






  

    2018-06-04
    CZ.NIC