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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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NAME | INTRODUCTION | DESCRIPTION | TOOLS | EXAMPLE | SEE ALSO | COLOPHON |
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ORG.FRE...GCONTROL1(5) org.freedesktop.LogControl1ORG.FRE...GCONTROL1(5)
org.freedesktop.LogControl1 - D-Bus interface to query and set
logging configuration
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.
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.
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 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)))
static int log_error(int log_level, int error, const char *str) {
sd_journal_print(log_level, "%s failed: %s", str, strerror(-error));
return error;
}
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) {
int i;
for (i = 0; i < LOG_DEBUG + 1; i++)
if (strcmp(value, log_level_table[i]) == 0) {
o->log_level = i;
setlogmask(LOG_UPTO(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) {
LogTarget i;
for (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",
};
int r;
/* https://man7.org/linux/man-pages/man3/setlogmask.3.html
* Programs using syslog() instead of sd_journal can use this API to cut logs
* emission at the source.
*/
setlogmask(LOG_UPTO(o.log_level));
/* Acquire a connection to the bus, letting the library work out the details.
* https://www.freedesktop.org/software/systemd/man/sd_bus_default.html
*/
r = sd_bus_default(&bus);
if (r < 0)
return log_error(o.log_level, r, "sd_bus_default()");
/* 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
*/
r = sd_bus_add_object_vtable(bus, NULL,
"/org/freedesktop/LogControl1",
"org.freedesktop.LogControl1",
vtable,
&o);
if (r < 0)
return log_error(o.log_level, r, "sd_bus_add_object_vtable()");
/* 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
*/
r = sd_bus_request_name(bus, "org.freedesktop.Example", 0);
if (r < 0)
return log_error(o.log_level, r, "sd_bus_request_name()");
for (;;) {
/* https://www.freedesktop.org/software/systemd/man/sd_bus_wait.html
*/
r = sd_bus_wait(bus, UINT64_MAX);
if (r < 0)
return log_error(o.log_level, r, "sd_bus_wait()");
/* https://www.freedesktop.org/software/systemd/man/sd_bus_process.html
*/
r = sd_bus_process(bus, NULL);
if (r < 0)
return log_error(o.log_level, r, "sd_bus_process()");
}
/* https://www.freedesktop.org/software/systemd/man/sd_bus_release_name.html
*/
r = sd_bus_release_name(bus, "org.freedesktop.Example");
if (r < 0)
return log_error(o.log_level, r, "sd_bus_release_name()");
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).
systemd(1), journalctl(1), systemctl(1), systemd.service(5),
syslog(3)
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have
a bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2024-06-13.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
systemd 257~devel ORG.FRE...GCONTROL1(5)
Pages that refer to this page: systemctl(1), systemd(1), systemd.directives(7), systemd.index(7), systemd-hostnamed.service(8), systemd-importd.service(8), systemd-localed.service(8), systemd-logind.service(8), systemd-machined.service(8), systemd-resolved.service(8), systemd-timedated.service(8)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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