org.freedesktop.LogControl1

systemd

D-Bus interface to query and set logging configuration

Introduction

org.freedesktop.LogControl1 is a generic interface that is intended to be used by any daemon which allows the log level and target to be set over D-Bus. It is implemented by various daemons that are part of the systemd(1) suite.

It is assumed that those settings are global for the whole program, so a fixed object path is used. The interface should always be available under the path /org/freedesktop/LogControl1.

Description

The following interface is exposed:

node /org/freedesktop/LogControl1 {
  interface org.freedesktop.LogControl1 {
    properties:
      @org.freedesktop.DBus.Property.EmitsChangedSignal("false")
      @org.freedesktop.systemd1.Privileged("true")
      readwrite s LogLevel = '...';
      @org.freedesktop.DBus.Property.EmitsChangedSignal("false")
      @org.freedesktop.systemd1.Privileged("true")
      readwrite s LogTarget = '...';
      @org.freedesktop.DBus.Property.EmitsChangedSignal("false")
      readonly s SyslogIdentifier = '...';
  };
  interface org.freedesktop.DBus.Peer { ... };
  interface org.freedesktop.DBus.Introspectable { ... };
  interface org.freedesktop.DBus.Properties { ... };
};

Properties

LogLevel describes the syslog(3)-style log-level, and should be one of emerg, alert, crit, err, warning, notice, info, debug, in order of increasing verbosity.

LogTarget describes the log target (mechanism). It should be one of console (log to the console or standard output), kmsg (log to the kernel ring buffer), journal (log to the journal natively, see systemd-journald.service(8)), syslog (log using the syslog(3) call).

[!CAUTION] The LogLevel and LogTarget properties are supposed to be writable. Care should be taken to ensure that only appropriately privileged clients can modify them.

SyslogIdentifier is a read-only property that shows the "syslog identifier". It is a short string that identifies the program that is the source of log messages that is passed to the syslog(3) call.

Tools

journalctl option -p/--priority= may be used to filter log messages by log level, option -t/--identifier= may be used to by the syslog identifier, and filters like _TRANSPORT=syslog, _TRANSPORT=journal, and _TRANSPORT=kernel may be used to filter messages by the mechanism through which they reached systemd-journald.

systemctl log-level and systemctl log-target verbs may be used to query and set the LogLevel and LogTarget properties of the service manager. systemctl service-log-level and systemctl service-log-target may similarly be used for individual services. (Services must have the BusName= property set and must implement the interface described here. See systemd.service(5) for details about BusName=.)

Example

Create a simple listener on the bus that implements LogControl1

This creates a simple server on the bus. It implements the LogControl1 interface by providing the required properties and allowing to set the writable ones. It logs at the configured log level using sd_journal_print(3).

Note that when porting this example to other D-Bus libraries it might be necessary to add manual client privilege checks, as they typically do not default to the restrictive defaults of sd-bus, where unprivileged access to properties is controlled via the SD_BUS_VTABLE_UNPRIVILEGED flag that is opt-in rather than opt-out.