set syslog priority and do not write level and date to syslog (#4923) (#5296)

When writing log entries to syslog, pass the level (WARN, INFO, etc)
directly to syslog. Avoid writing level and date. This provides a
better integration and allows to use syslog search tools.

docs/2-usage/17-log-management.md

@@ -1,35 +0,0 @@
-# Log management
-
-By default, log entries are printed on the console (stdout). It is possible to write logs to a file by using the `logDestinations` and `logFile` settings:
-
-```yml
-# Destinations of log messages; available values are "stdout", "file" and "syslog".
-logDestinations: [file]
-# If "file" is in logDestinations, this is the file which will receive the logs.
-logFile: mediamtx.log
-```
-
-The log file can be periodically rotated or truncated by using an external utility.
-
-On most Linux distributions, the `logrotate` utility is in charge of managing log files. It can be configured to handle the _MediaMTX_ log file too by creating a configuration file, placed in `/etc/logrotate.d/mediamtx`, with this content:
-
-```
-/my/mediamtx/path/mediamtx.log {
-    daily
-    copytruncate
-    rotate 7
-    compress
-    delaycompress
-    missingok
-    notifempty
-}
-```
-
-This file will rotate the log file every day, adding a `.NUMBER` suffix to older copies:
-
-```
-mediamtx.log.1
-mediamtx.log.2
-mediamtx.log.3
-...
-```

docs/2-usage/17-logging.md

@@ -0,0 +1,71 @@
+# Logging
+
+## Log verbosity
+
+Log verbosity can be set with the `logLevel` parameter:
+
+```yml
+# Verbosity of the program; available values are "error", "warn", "info", "debug".
+logLevel: info
+```
+
+## Log destinations
+
+Log entries can be sent to multiple destinations. By default, they are printed on the console (stdout).
+
+It is possible to write logs to a file by using these parameters:
+
+```yml
+# Destinations of log messages; available values are "stdout", "file" and "syslog".
+logDestinations: [file]
+# If "file" is in logDestinations, this is the file which will receive the logs.
+logFile: mediamtx.log
+```
+
+It is possible to write logs to the system logging server (syslog) by using these parameters:
+
+```yml
+# Destinations of log messages; available values are "stdout", "file" and "syslog".
+logDestinations: [syslog]
+# If "syslog" is in logDestinations, use prefix for logs.
+sysLogPrefix: mediamtx
+```
+
+Log entries can be queried by using:
+
+```sh
+journalctl SYSLOG_IDENTIFIER=mediamtx
+```
+
+If _MediaMTX_ is also running as a [system service](start-on-boot), log entries can be queried by using:
+
+```sh
+journalctl -u mediamtx
+```
+
+## Log file rotation
+
+The log file can be periodically rotated or truncated by using an external utility.
+
+On most Linux distributions, the `logrotate` utility is in charge of managing log files. It can be configured to handle the _MediaMTX_ log file too by creating a configuration file, placed in `/etc/logrotate.d/mediamtx`, with this content:
+
+```
+/my/mediamtx/path/mediamtx.log {
+    daily
+    copytruncate
+    rotate 7
+    compress
+    delaycompress
+    missingok
+    notifempty
+}
+```
+
+This file will rotate the log file every day, adding a `.NUMBER` suffix to older copies:
+
+```
+mediamtx.log.1
+mediamtx.log.2
+mediamtx.log.3
+...
+```

internal/logger/destination_file.go

@@ -2,6 +2,7 @@ package logger
 
 import (
 	"bytes"
+	"fmt"
 	"os"
 	"time"
 )
@@ -26,7 +27,8 @@ func (d *destinationFile) log(t time.Time, level Level, format string, args ...a
 	d.buf.Reset()
 	writeTime(&d.buf, t, false)
 	writeLevel(&d.buf, level, false)
-	writeContent(&d.buf, format, args)
+	fmt.Fprintf(&d.buf, format, args...)
+	d.buf.WriteByte('\n')
 	d.file.Write(d.buf.Bytes()) //nolint:errcheck
 }
 

internal/logger/destination_stdout.go

@@ -2,6 +2,7 @@ package logger
 
 import (
 	"bytes"
+	"fmt"
 	"os"
 	"time"
 
@@ -10,8 +11,7 @@ import (
 
 type destinationStdout struct {
 	useColor bool
-
-	buf bytes.Buffer
+	buf      bytes.Buffer
 }
 
 func newDestionationStdout() destination {
@@ -24,7 +24,8 @@ func (d *destinationStdout) log(t time.Time, level Level, format string, args ..
 	d.buf.Reset()
 	writeTime(&d.buf, t, d.useColor)
 	writeLevel(&d.buf, level, d.useColor)
-	writeContent(&d.buf, format, args)
+	fmt.Fprintf(&d.buf, format, args...)
+	d.buf.WriteByte('\n')
 	os.Stdout.Write(d.buf.Bytes()) //nolint:errcheck
 }
 

internal/logger/destination_syslog.go

@@ -1,18 +1,21 @@
+//go:build !darwin && !windows
+
 package logger
 
 import (
 	"bytes"
-	"io"
+	"fmt"
+	"log/syslog"
 	"time"
 )
 
 type destinationSysLog struct {
-	syslog io.WriteCloser
+	syslog *syslog.Writer
 	buf    bytes.Buffer
 }
 
 func newDestinationSyslog(prefix string) (destination, error) {
-	syslog, err := newSysLog(prefix)
+	syslog, err := syslog.New(syslog.LOG_DAEMON, prefix)
 	if err != nil {
 		return nil, err
 	}
@@ -22,14 +25,23 @@ func newDestinationSyslog(prefix string) (destination, error) {
 	}, nil
 }
 
-func (d *destinationSysLog) log(t time.Time, level Level, format string, args ...any) {
+func (d *destinationSysLog) log(_ time.Time, level Level, format string, args ...any) {
 	d.buf.Reset()
-	writeTime(&d.buf, t, false)
-	writeLevel(&d.buf, level, false)
-	writeContent(&d.buf, format, args)
-	d.syslog.Write(d.buf.Bytes()) //nolint:errcheck
+
+	fmt.Fprintf(&d.buf, format, args...)
+
+	switch level {
+	case Debug:
+		d.syslog.Debug(d.buf.String()) //nolint:errcheck
+	case Info:
+		d.syslog.Info(d.buf.String()) //nolint:errcheck
+	case Warn:
+		d.syslog.Warning(d.buf.String()) //nolint:errcheck
+	case Error:
+		d.syslog.Err(d.buf.String()) //nolint:errcheck
+	}
 }
 
 func (d *destinationSysLog) close() {
-	d.syslog.Close()
+	d.syslog.Close() //nolint:errcheck
 }

internal/logger/destination_syslog_disabled.go

@@ -0,0 +1,9 @@
+//go:build darwin || windows
+
+package logger
+
+import "fmt"
+
+func newDestinationSyslog(_ string) (destination, error) {
+	return nil, fmt.Errorf("syslog is not available on macOS and Windows")
+}

internal/logger/logger.go

@@ -3,7 +3,6 @@ package logger
 
 import (
 	"bytes"
-	"fmt"
 	"sync"
 	"time"
 
@@ -135,11 +134,6 @@ func writeLevel(buf *bytes.Buffer, level Level, useColor bool) {
 	buf.WriteByte(' ')
 }
 
-func writeContent(buf *bytes.Buffer, format string, args []any) {
-	fmt.Fprintf(buf, format, args...)
-	buf.WriteByte('\n')
-}
-
 // Log writes a log entry.
 func (lh *Logger) Log(level Level, format string, args ...any) {
 	if level < lh.level {

internal/logger/syslog_darwin.go

@@ -1,12 +0,0 @@
-//go:build darwin
-
-package logger
-
-import (
-	"fmt"
-	"io"
-)
-
-func newSysLog(_ string) (io.WriteCloser, error) {
-	return nil, fmt.Errorf("unavailable on macOS")
-}

internal/logger/syslog_unix.go

@@ -1,31 +0,0 @@
-//go:build !windows && !darwin
-
-package logger
-
-import (
-	"io"
-	native "log/syslog"
-)
-
-type syslog struct {
-	inner *native.Writer
-}
-
-func newSysLog(prefix string) (io.WriteCloser, error) {
-	inner, err := native.New(native.LOG_INFO|native.LOG_DAEMON, prefix)
-	if err != nil {
-		return nil, err
-	}
-
-	return &syslog{
-		inner: inner,
-	}, nil
-}
-
-func (ls *syslog) Close() error {
-	return ls.inner.Close()
-}
-
-func (ls *syslog) Write(p []byte) (int, error) {
-	return ls.inner.Write(p)
-}

internal/logger/syslog_win.go

@@ -1,12 +0,0 @@
-//go:build windows
-
-package logger
-
-import (
-	"fmt"
-	"io"
-)
-
-func newSysLog(_ string) (io.WriteCloser, error) {
-	return nil, fmt.Errorf("unavailable on Windows")
-}

mediamtx.yml

@@ -10,7 +10,7 @@
 logLevel: info
 # Destinations of log messages; available values are "stdout", "file" and "syslog".
 logDestinations: [stdout]
-# If "file" is in logDestinations, this is the file which will receive the logs.
+# If "file" is in logDestinations, this is the file which will receive logs.
 logFile: mediamtx.log
 # If "syslog" is in logDestinations, use prefix for logs.
 sysLogPrefix: mediamtx