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|
'\" t
.TH "ORG\&.FREEDESKTOP\&.LOGCONTROL1" "5" "" "systemd 254" "org.freedesktop.LogControl1"
.\" -----------------------------------------------------------------
.\" * Define some portability stuff
.\" -----------------------------------------------------------------
.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.\" http://bugs.debian.org/507673
.\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html
.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.ie \n(.g .ds Aq \(aq
.el .ds Aq '
.\" -----------------------------------------------------------------
.\" * set default formatting
.\" -----------------------------------------------------------------
.\" disable hyphenation
.nh
.\" disable justification (adjust text to left margin only)
.ad l
.\" -----------------------------------------------------------------
.\" * MAIN CONTENT STARTS HERE *
.\" -----------------------------------------------------------------
.SH "NAME"
org.freedesktop.LogControl1 \- D\-Bus interface to query and set logging configuration
.SH "INTRODUCTION"
.PP
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
\fBsystemd\fR(1)
suite\&.
.PP
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\&.
.SH "DESCRIPTION"
.PP
The following interface is exposed:
.sp
.if n \{\
.RS 4
.\}
.nf
node /org/freedesktop/LogControl1 {
interface org\&.freedesktop\&.LogControl1 {
properties:
@org\&.freedesktop\&.DBus\&.Property\&.EmitsChangedSignal("false")
@org\&.freedesktop\&.systemd1\&.Privileged("true")
readwrite s LogLevel = \*(Aq\&.\&.\&.\*(Aq;
@org\&.freedesktop\&.DBus\&.Property\&.EmitsChangedSignal("false")
@org\&.freedesktop\&.systemd1\&.Privileged("true")
readwrite s LogTarget = \*(Aq\&.\&.\&.\*(Aq;
@org\&.freedesktop\&.DBus\&.Property\&.EmitsChangedSignal("false")
readonly s SyslogIdentifier = \*(Aq\&.\&.\&.\*(Aq;
};
interface org\&.freedesktop\&.DBus\&.Peer { \&.\&.\&. };
interface org\&.freedesktop\&.DBus\&.Introspectable { \&.\&.\&. };
interface org\&.freedesktop\&.DBus\&.Properties { \&.\&.\&. };
};
.fi
.if n \{\
.RE
.\}
.SS "Properties"
.PP
\fILogLevel\fR
describes the
\fBsyslog\fR(3)\-style log\-level, and should be one of
"emerg",
"alert",
"crit",
"err",
"warning",
"notice",
"info",
"debug", in order of increasing verbosity\&.
.PP
\fILogTarget\fR
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
\fBsystemd-journald.service\fR(8)),
"syslog"
(log using the
\fBsyslog\fR(3)
call)\&.
.PP
Those two properties are writable, so they may be set by sufficiently privileged users\&.
.PP
\fISyslogIdentifier\fR
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
\fBsyslog\fR(3)
call\&.
.SH "TOOLS"
.PP
\fBjournalctl\fR
option
\fB\-p\fR/\fB\-\-priority=\fR
may be used to filter log messages by log level, option
\fB\-t\fR/\fB\-\-identifier=\fR
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
\fBsystemd\-journald\fR\&.
.PP
\fBsystemctl log\-level\fR
and
\fBsystemctl log\-target\fR
verbs may be used to query and set the
\fILogLevel\fR
and
\fILogTarget\fR
properties of the service manager\&.
\fBsystemctl service\-log\-level\fR
and
\fBsystemctl service\-log\-target\fR
may similarly be used for individual services\&. (Services must have the
\fIBusName=\fR
property set and must implement the interface described here\&. See
\fBsystemd.service\fR(5)
for details about
\fIBusName=\fR\&.)
.SH "EXAMPLE"
.PP
\fBExample\ \&1.\ \&Create a simple listener on the bus that implements LogControl1\fR
.sp
.if n \{\
.RS 4
.\}
.nf
/* 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 \*(Aqcc logcontrol\-example\&.c $(pkg\-config \-\-libs \-\-cflags libsystemd)\*(Aq
*
* To get and set properties via busctl:
*
* $ busctl \-\-user get\-property org\&.freedesktop\&.Example \e
* /org/freedesktop/LogControl1 \e
* org\&.freedesktop\&.LogControl1 \e
* SyslogIdentifier
* s "example"
* $ busctl \-\-user get\-property org\&.freedesktop\&.Example \e
* /org/freedesktop/LogControl1 \e
* org\&.freedesktop\&.LogControl1 \e
* LogTarget
* s "journal"
* $ busctl \-\-user get\-property org\&.freedesktop\&.Example \e
* /org/freedesktop/LogControl1 \e
* org\&.freedesktop\&.LogControl1 \e
* LogLevel
* s "info"
* $ busctl \-\-user set\-property org\&.freedesktop\&.Example \e
* /org/freedesktop/LogControl1 \e
* org\&.freedesktop\&.LogControl1 \e
* LogLevel \e
* "s" debug
* $ busctl \-\-user get\-property org\&.freedesktop\&.Example \e
* /org/freedesktop/LogControl1 \e
* org\&.freedesktop\&.LogControl1 \e
* 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) ({ \e
int _r = (x); \e
errno = _r < 0 ? \-_r : 0; \e
sd_journal_print((log_level), #x ": %m"); \e
if (_r < 0) \e
return EXIT_FAILURE; \e
})
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 \*(Aq%s\*(Aq",
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;
setlogmask(LOG_UPTO(i));
return 0;
}
return sd_bus_error_setf(error,
SD_BUS_ERROR_INVALID_ARGS,
"Invalid value for LogLevel: \*(Aq%s\*(Aq",
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: \*(Aq%s\*(Aq",
value);
}
return sd_bus_error_setf(error,
SD_BUS_ERROR_UNKNOWN_PROPERTY,
"Unknown property \*(Aq%s\*(Aq",
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",
};
/* 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
*/
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;
}
.fi
.if n \{\
.RE
.\}
.PP
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
\fBsd_journal_print\fR(3)\&.
.SH "SEE ALSO"
.PP
\fBsystemd\fR(1),
\fBjournalctl\fR(1),
\fBsystemctl\fR(1),
\fBsystemd.service\fR(5),
\fBsyslog\fR(3)
|
