Running and Operating

PowerDNS is normally controlled via a SysV-style init.d script, often located in /etc/init.d or /etc/rc.d/init.d. For Linux distributions with systemd, a service file is provided (either in the package or in the contrib directory of the tarball).

Furthermore, PowerDNS can be run on the foreground for testing or in other init- systems that supervise processes.

Guardian

When the init-system of the Operating System does not properly supervises processes, like SysV init, it is recommended to run PowerDNS with the guardian option set to ‘yes’.

When launched with guardian=yes, pdns_server wraps itself inside a ‘guardian’. This guardian monitors the performance of the inner pdns_server instance which shows up in the process list of your OS as pdns_server-instance. It is also this guardian that pdns_control talks to. A STOP is interpreted by the guardian, which causes the guardian to sever the connection to the inner process and terminate it, after which it terminates itself. Requests that require data from the actual nameserver are passed to the inner process as well.

Logging to syslog on systemd-based operating systems

By default, logging to syslog is disabled in the the systemd unit file to prevent the service logging twice, as the systemd journal picks up the output from the process itself.

Removing the --disable-syslog option from the ExecStart line using systemctl edit --full pdns enables logging to syslog.

Logging to syslog

This chapter assumes familiarity with syslog, the unix logging device. PowerDNS logs messages with different levels. The more urgent the message, the lower the ‘priority’.

By default, PowerDNS will only log messages with an urgency of 3 or lower, but this can be changed using the loglevel setting in the configuration file. Setting it to 0 will eliminate all logging, 9 will log everything.

By default, logging is performed under the ‘DAEMON’ facility which is shared with lots of other programs. If you regard nameserving as important, you may want to have it under a dedicated facility so PowerDNS can log to its own files, and not clutter generic files.

For this purpose, syslog knows about ‘local’ facilities, numbered from LOCAL0 to LOCAL7. To move PowerDNS logging to LOCAL0, add logging-facility=0 to your configuration.

Furthermore, you may want to have separate files for the differing priorities - preventing lower priority messages from obscuring important ones. A sample syslog.conf might be:

local0.info                       -/var/log/pdns.info
local0.warn                       -/var/log/pdns.warn
local0.err                        /var/log/pdns.err

Where local0.err would store the really important messages. For performance and disk space reasons, it is advised to audit your syslog.conf for statements also logging PowerDNS activities. Many syslog.confs have a *.* statement to /var/log/syslog, which you may want to remove.

For performance reasons, be especially certain that no large amounts of synchronous logging take place. Under Linux, this is indicated by file names not starting with a - - indicating a synchronous log, which hurts performance.

Be aware that syslog by default logs messages at the configured priority and higher! To log only info messages, use local0.=info

Controlling A Running PowerDNS Server

As a DNS server is critical infrastructure, downtimes should be avoided as much as possible. Even though PowerDNS (re)starts very fast, it offers a way to control it while running.

Control Socket

The controlsocket is the means to contact a running PowerDNS process. Over this socket, instructions can be sent using the pdns_control program. The control socket is called pdns.controlsocket and is created inside the socket-dir.

pdns_control

To communicate with PowerDNS Authoritative Server over the controlsocket, the pdns_control command is used. The syntax is simple: pdns_control command arguments. Currently this is most useful for telling backends to rediscover domains or to force the transmission of notifications. See Master operation.

For all supported pdns_control commands and options, see the manpage and the output of pdns_control --help on your system.

The SysV init script

This script supplied with the PowerDNS source accepts the following commands:

  • monitor: Monitor is a special way to view the daemon. It executes PowerDNS in the foreground with a lot of logging turned on, which helps in determining startup problems. Besides running in the foreground, the raw PowerDNS control socket is made available. All external communication with the daemon is normally sent over this socket. While useful, the control console is not an officially supported feature. Commands which work are: QUIT, SHOW *, SHOW varname, RPING.
  • start: Start PowerDNS in the background. Launches the daemon but makes no special effort to determine success, as making database connections may take a while. Use status to query success. You can safely run start many times, it will not start additional PowerDNS instances.
  • restart: Restarts PowerDNS if it was running, starts it otherwise.
  • status: Query PowerDNS for status. This can be used to figure out if a launch was successful. The status found is prefixed by the PID of the main PowerDNS process.
  • stop: Requests that PowerDNS stop. Again, does not confirm success. Success can be ascertained with the status command.
  • dump: Dumps a lot of statistics of a running PowerDNS daemon. It is also possible to single out specific variable by using the show command.
  • show variable: Show a single statistic, as present in the output of the dump.
  • mrtg: Dump statistics in mrtg format. See the performance Counters documentation.

Note

Packages provided by Operating System vendors might support different or less commands.

Running in the foreground

One can run PowerDNS in the foreground by invoking the pdns_server executable. Without any options, it will load the pdns.conf and run. To make sure PowerDNS starts in the foreground, add the --daemon=no option.

All settings can be added on the commandline. e.g. to test a new database config, you could start PowerDNS like this:

pdns_server --no-config --daemon=no --local-port=5300 --launch=gmysql --gmysql-user=my_user --gmysql-password=mypassword

This starts PowerDNS without loading on-disk config, in the foreground, on all network interfaces on port 5300 and starting the gmysql backend.