diff --git a/CMakeLists.txt b/CMakeLists.txt
index 060dd37..9cbd01e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -20,6 +20,7 @@ add_executable(FlashMQ
     rwlockguard.cpp
     retainedmessage.cpp
     cirbuf.cpp
+    logger.cpp
     )
 
 target_link_libraries(FlashMQ pthread)
diff --git a/FlashMQTests/FlashMQTests.pro b/FlashMQTests/FlashMQTests.pro
index 1213ae3..281e8fc 100644
--- a/FlashMQTests/FlashMQTests.pro
+++ b/FlashMQTests/FlashMQTests.pro
@@ -25,6 +25,7 @@ SOURCES +=  tst_maintests.cpp \
     ../threaddata.cpp \
     ../types.cpp \
     ../utils.cpp \
+    ../logger.cpp \
     mainappthread.cpp \
     twoclienttestcontext.cpp
 
@@ -42,5 +43,6 @@ HEADERS += \
     ../threaddata.h \
     ../types.h \
     ../utils.h \
+    ../logger.h \
     mainappthread.h \
     twoclienttestcontext.h
diff --git a/logger.cpp b/logger.cpp
new file mode 100644
index 0000000..5a534df
--- /dev/null
+++ b/logger.cpp
@@ -0,0 +1,79 @@
+#include "logger.h"
+#include <ctime>
+#include <sstream>
+#include <iomanip>
+
+Logger *Logger::instance = nullptr;
+
+Logger::Logger()
+{
+
+}
+
+std::string Logger::getLogLevelString(int level) const
+{
+    switch (level)
+    {
+    case LOG_NONE:
+        return "NONE";
+    case LOG_INFO:
+        return "INFO";
+    case LOG_NOTICE:
+        return "NOTICE";
+    case LOG_WARNING:
+        return "WARNING";
+    case LOG_ERR:
+        return "ERROR";
+    case LOG_DEBUG:
+        return "DEBUG";
+    default:
+        return "UNKNOWN LOG LEVEL";
+    }
+}
+
+Logger *Logger::getInstance()
+{
+    if (instance == nullptr)
+        instance = new Logger();
+    return instance;
+}
+
+void Logger::logf(int level, const char *str, ...)
+{
+    if (level > curLogLevel)
+        return;
+
+    std::lock_guard<std::mutex> locker(logMutex);
+
+    time_t time = std::time(nullptr);
+    struct tm tm = *std::localtime(&time);
+    std::ostringstream oss;
+
+    std::string str_(str);
+    oss << "[" << std::put_time(&tm, "%Y-%m-%d %H:%M:%S") << "] [" << getLogLevelString(level) << "] " << str_;
+    oss.flush();
+    const std::string s = oss.str();
+    const char *logfmtstring = s.c_str();
+
+    va_list valist;
+    va_start(valist, str);
+    if (this->file)
+    {
+        vfprintf(this->file, logfmtstring, valist);
+        fprintf(this->file, "\n");
+        fflush(this->file);
+    }
+    else
+    {
+#ifdef TESTING
+        vfprintf(stderr, logfmtstring, valist); // the stdout interfers with Qt test XML output, so using stderr.
+        fprintf(stderr, "\n");
+        fflush(stderr);
+#else
+        vfprintf(stdout, logfmtstring, valist);
+        fprintf(stdout, "\n");
+        fflush(stdout);
+#endif
+    }
+    va_end(valist);
+}
diff --git a/logger.h b/logger.h
new file mode 100644
index 0000000..9d88422
--- /dev/null
+++ b/logger.h
@@ -0,0 +1,32 @@
+#ifndef LOGGER_H
+#define LOGGER_H
+
+#include <stdio.h>
+#include <stdarg.h>
+#include <mutex>
+
+// Compatible with Mosquitto, for auth plugin compatability.
+#define LOG_NONE 0x00
+#define LOG_INFO 0x01
+#define LOG_NOTICE 0x02
+#define LOG_WARNING 0x04
+#define LOG_ERR 0x08
+#define LOG_DEBUG 0x10
+
+class Logger
+{
+    static Logger *instance;
+    int curLogLevel = LOG_DEBUG;
+    std::mutex logMutex;
+    FILE *file = nullptr;
+
+    Logger();
+    std::string getLogLevelString(int level) const;
+
+public:
+    static Logger *getInstance();
+    void logf(int level, const char *str, ...);
+
+};
+
+#endif // LOGGER_H