ORG.FREEDESKTOP.LOGCONTROLorg.freedesktop.LogConORG.FREEDESKTOP.LOGCONTROL1(5)
NAME
org.freedesktop.LogControl1 - 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).
Those two properties are writable, so they may be set by sufficiently
privileged users.
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
Example 1. Create a simple listener on the bus that implements
LogControl1
/* SPDX-License-Identifier: MIT-0 */
/* Implements the LogControl1 interface as per specification:
* https://www.freedesktop.org/software/systemd/man/org.freedesktop.LogControl1.html
*
* Compile with 'cc logcontrol-example.c $(pkg-config --libs --cflags libsystemd)'
*
* To get and set properties via busctl:
*
* $ busctl --user get-property org.freedesktop.Example \
* /org/freedesktop/LogControl1 \
* org.freedesktop.LogControl1 \
* SyslogIdentifier
* s "example"
* $ busctl --user get-property org.freedesktop.Example \
* /org/freedesktop/LogControl1 \
* org.freedesktop.LogControl1 \
* LogTarget
* s "journal"
* $ busctl --user get-property org.freedesktop.Example \
* /org/freedesktop/LogControl1 \
* org.freedesktop.LogControl1 \
* LogLevel
* s "info"
* $ busctl --user set-property org.freedesktop.Example \
* /org/freedesktop/LogControl1 \
* org.freedesktop.LogControl1 \
* LogLevel \
* "s" debug
* $ busctl --user get-property org.freedesktop.Example \
* /org/freedesktop/LogControl1 \
* org.freedesktop.LogControl1 \
* LogLevel
* s "debug"
*/
#include <errno.h>
#include <stdlib.h>
#include <stdio.h>
#include <syslog.h>
#include <systemd/sd-bus.h>
#include <systemd/sd-journal.h>
#define _cleanup_(f) __attribute__((cleanup(f)))
#define check(log_level, x) ({ \
int _r = (x); \
errno = _r < 0 ? -_r : 0; \
sd_journal_print((log_level), #x ": %m"); \
if (_r < 0) \
return EXIT_FAILURE; \
})
typedef enum LogTarget {
LOG_TARGET_JOURNAL,
LOG_TARGET_KMSG,
LOG_TARGET_SYSLOG,
LOG_TARGET_CONSOLE,
_LOG_TARGET_MAX,
} LogTarget;
static const char* const log_target_table[_LOG_TARGET_MAX] = {
[LOG_TARGET_JOURNAL] = "journal",
[LOG_TARGET_KMSG] = "kmsg",
[LOG_TARGET_SYSLOG] = "syslog",
[LOG_TARGET_CONSOLE] = "console",
};
static const char* const log_level_table[LOG_DEBUG + 1] = {
[LOG_EMERG] = "emerg",
[LOG_ALERT] = "alert",
[LOG_CRIT] = "crit",
[LOG_ERR] = "err",
[LOG_WARNING] = "warning",
[LOG_NOTICE] = "notice",
[LOG_INFO] = "info",
[LOG_DEBUG] = "debug",
};
typedef struct object {
const char *syslog_identifier;
LogTarget log_target;
int log_level;
} object;
static int property_get(
sd_bus *bus,
const char *path,
const char *interface,
const char *property,
sd_bus_message *reply,
void *userdata,
sd_bus_error *error) {
object *o = userdata;
if (strcmp(property, "LogLevel") == 0)
return sd_bus_message_append(reply, "s", log_level_table[o->log_level]);
if (strcmp(property, "LogTarget") == 0)
return sd_bus_message_append(reply, "s", log_target_table[o->log_target]);
if (strcmp(property, "SyslogIdentifier") == 0)
return sd_bus_message_append(reply, "s", o->syslog_identifier);
return sd_bus_error_setf(error,
SD_BUS_ERROR_UNKNOWN_PROPERTY,
"Unknown property '%s'",
property);
}
static int property_set(
sd_bus *bus,
const char *path,
const char *interface,
const char *property,
sd_bus_message *message,
void *userdata,
sd_bus_error *error) {
object *o = userdata;
const char *value;
int r;
r = sd_bus_message_read(message, "s", &value);
if (r < 0)
return r;
if (strcmp(property, "LogLevel") == 0) {
for (int i = 0; i < LOG_DEBUG + 1; i++)
if (strcmp(value, log_level_table[i]) == 0) {
o->log_level = i;
return 0;
}
return sd_bus_error_setf(error,
SD_BUS_ERROR_INVALID_ARGS,
"Invalid value for LogLevel: '%s'",
value);
}
if (strcmp(property, "LogTarget") == 0) {
for (LogTarget i = 0; i < _LOG_TARGET_MAX; i++)
if (strcmp(value, log_target_table[i]) == 0) {
o->log_target = i;
return 0;
}
return sd_bus_error_setf(error,
SD_BUS_ERROR_INVALID_ARGS,
"Invalid value for LogTarget: '%s'",
value);
}
return sd_bus_error_setf(error,
SD_BUS_ERROR_UNKNOWN_PROPERTY,
"Unknown property '%s'",
property);
}
/* https://www.freedesktop.org/software/systemd/man/sd_bus_add_object.html
*/
static const sd_bus_vtable vtable[] = {
SD_BUS_VTABLE_START(0),
SD_BUS_WRITABLE_PROPERTY(
"LogLevel", "s",
property_get, property_set,
0,
0),
SD_BUS_WRITABLE_PROPERTY(
"LogTarget", "s",
property_get, property_set,
0,
0),
SD_BUS_PROPERTY(
"SyslogIdentifier", "s",
property_get,
0,
SD_BUS_VTABLE_PROPERTY_CONST),
SD_BUS_VTABLE_END
};
int main(int argc, char **argv) {
/* The bus should be relinquished before the program terminates. The cleanup
* attribute allows us to do it nicely and cleanly whenever we exit the
* block.
*/
_cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
object o = {
.log_level = LOG_INFO,
.log_target = LOG_TARGET_JOURNAL,
.syslog_identifier = "example",
};
/* Acquire a connection to the bus, letting the library work out the details.
* https://www.freedesktop.org/software/systemd/man/sd_bus_default.html
*/
check(o.log_level, sd_bus_default(&bus));
/* Publish an interface on the bus, specifying our well-known object access
* path and public interface name.
* https://www.freedesktop.org/software/systemd/man/sd_bus_add_object.html
* https://dbus.freedesktop.org/doc/dbus-tutorial.html
*/
check(o.log_level, sd_bus_add_object_vtable(bus, NULL,
"/org/freedesktop/LogControl1",
"org.freedesktop.LogControl1",
vtable,
&o));
/* By default the service is assigned an ephemeral name. Also add a fixed
* one, so that clients know whom to call.
* https://www.freedesktop.org/software/systemd/man/sd_bus_request_name.html
*/
check(o.log_level, sd_bus_request_name(bus, "org.freedesktop.Example", 0));
for (;;) {
/* https://www.freedesktop.org/software/systemd/man/sd_bus_wait.html
*/
check(o.log_level, sd_bus_wait(bus, UINT64_MAX));
/* https://www.freedesktop.org/software/systemd/man/sd_bus_process.html
*/
check(o.log_level, sd_bus_process(bus, NULL));
}
/* https://www.freedesktop.org/software/systemd/man/sd_bus_release_name.html
*/
check(o.log_level, sd_bus_release_name(bus, "org.freedesktop.Example"));
return 0;
}
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).
SEE ALSO
systemd(1), journalctl(1), systemctl(1), systemd.service(5), syslog(3)
systemd 252 ORG.FREEDESKTOP.LOGCONTROL1(5)
Generated by dwww version 1.15 on Wed Jun 26 00:42:25 CEST 2024.