diff --git a/build.sh b/build.sh
index 21f9429..694a80b 100755
--- a/build.sh
+++ b/build.sh
@@ -11,5 +11,5 @@ else
 	c++ -Wall -DNDEBUG -O3 *.cpp $OPTS -o icetunnel2
 fi
 
-
+echo done
 
diff --git a/common.cpp b/common.cpp
index d45d69f..15ecd60 100644
--- a/common.cpp
+++ b/common.cpp
@@ -9,7 +9,7 @@
 
 
 void Address::print() const
-	{ printf("%hhu.%hhu.%hhu.%hhu:%hu", ip[0], ip[1], ip[2], ip[3], port); }
+	{ logf("%hhu.%hhu.%hhu.%hhu:%hu", ip[0], ip[1], ip[2], ip[3], port); }
 
 
 Time monotonicTime() {
diff --git a/common.h b/common.h
index ae39f67..25165b7 100644
--- a/common.h
+++ b/common.h
@@ -5,16 +5,18 @@
 #include <cstdio>
 
 
+#define logf(...) do { fprintf(stdout, __VA_ARGS__); fflush(stdout); } while(0)
+
+
 #define HideDebugMSG(...) do {} while(0)
 
 #ifdef NDEBUG
 #	define ShowDebugMSG(...) do {} while(0)
 #else
 #	define ShowDebugMSG(...) do { \
-		printf("DEBUG %16lld %s:%s:%d:", monotonicTime(), __FILE__, __func__, __LINE__); \
-		printf(" " __VA_ARGS__); \
-		printf("\n"); \
-		fflush(stdout); \
+		logf("DEBUG %16lld %s:%s:%d:", monotonicTime(), __FILE__, __func__, __LINE__); \
+		logf(" " __VA_ARGS__); \
+		logf("\n"); \
 	} while(0)
 #endif
 
diff --git a/main.cpp b/main.cpp
index 9ece38a..bfe0b63 100644
--- a/main.cpp
+++ b/main.cpp
@@ -6,44 +6,60 @@
 #include "tunnel.h"
 
 
-bool parseAddress(const char *str, Address &address) {
+static bool parseAddress(const char *str, Address &address) {
 	address = Address();
 	sscanf( str, "%hhu.%hhu.%hhu.%hhu:%hu",
 			&address.ip[0], &address.ip[1], &address.ip[2], &address.ip[3],
 			&address.port );
 	if (!address.port) {
-		printf("Wrong ip-address: [%s]\n", str);
+		logf("Wrong ip-address: [%s]\n", str);
 		return false;
 	}
 	return true;
 }
 
 
+static bool openLogFile(const char *logfile) {
+	if (0 != strcmp(logfile, "-")) {
+		bool eq = stderr == stdout;
+		stderr = stderr ? fopen(logfile, "a+") : freopen(logfile, "a+", stderr);
+		if (!stderr)
+			{ logf("Cannot open log file: %s\n", logfile); return false; }
+		if (!eq && stdout && stdout != stderr) fclose(stdout);
+		stdout = stderr;
+	}
+	return true;
+}
+
+
+
 int main(int argc, char **argv) {
 	
 	// parse args
 	
 	unsigned long long bytesPerSecond = 0;
 	Address localUdp, remoteUdp, localTcp, remoteTcp;
-	if (argc == 6) {
+	if (argc == 7) {
+		bool l = openLogFile(argv[6]);
 		sscanf(argv[2], "%llu", &bytesPerSecond);
 		if (!bytesPerSecond)
-			{ printf("Wrong bytes per second: %llu\n", bytesPerSecond); return 1; }
+			{ logf("Wrong bytes per second: %llu\n", bytesPerSecond); return 1; }
 		parseAddress(argv[3], localUdp);
 		parseAddress(argv[4], remoteUdp);
 		parseAddress(argv[5], localTcp);
-		if (!localUdp.port || !remoteUdp.port || !localTcp.port) return 1;
+		if (!localUdp.port || !remoteUdp.port || !localTcp.port || !l) return 1;
 	} else
-	if (argc == 5) {
+	if (argc == 6) {
+		bool l = openLogFile(argv[5]);
 		sscanf(argv[2], "%llu", &bytesPerSecond);
 		if (!bytesPerSecond)
-			{ printf("Wrong bytes per second: %llu\n", bytesPerSecond); return 1; }
+			{ logf("Wrong bytes per second: %llu\n", bytesPerSecond); return 1; }
 		parseAddress(argv[3], localUdp);
 		parseAddress(argv[4], remoteTcp);
-		if (!localUdp.port || !remoteTcp.port) return 1;
+		if (!localUdp.port || !remoteTcp.port || !l) return 1;
 	} else {
-		printf("Usage: %s keyfile bytesPerSecond localUdp:port remoteUdp:port localTcp:port\n", argv[0]);
-		printf("   or: %s keyfile bytesPerSecond localUdp:port remoteTcp:port\n", argv[0]);
+		logf("Usage: %s keyfile bytesPerSecond localUdp:port remoteUdp:port localTcp:port logfile|-\n", argv[0]);
+		logf("   or: %s keyfile bytesPerSecond localUdp:port remoteTcp:port logfile|-\n", argv[0]);
 		return 1;
 	}
 	
@@ -51,7 +67,7 @@ int main(int argc, char **argv) {
 	
 	FILE *f = fopen(argv[1], "r");
 	if (!f) {
-		printf("Cannot open keyfile: [%s]\n", argv[1]);
+		logf("Cannot open keyfile: [%s]\n", argv[1]);
 		return 1;
 	}
 	int maxSize = 1024*1024;
@@ -60,7 +76,7 @@ int main(int argc, char **argv) {
 	int i = 0;
 	while((i = fgetc(f)) > 0 && c < e) *c++ = i;
 	if (i != EOF || errno) {
-		printf("Cannot read keyfile: [%s]\n", argv[1]);
+		logf("Cannot read keyfile: [%s]\n", argv[1]);
 		memset(key, 0, maxSize);
 		free(key);
 		fclose(f);
diff --git a/tunnel.cpp b/tunnel.cpp
index 51be451..e938942 100644
--- a/tunnel.cpp
+++ b/tunnel.cpp
@@ -44,19 +44,19 @@ void Tunnel::initSpeed(unsigned long long bytesPerSecond) {
 
 bool Tunnel::initUdpServer(const Address &address, const Address &remoteTcpAddress, const char *key) {
 	closeUdpServer();
-	printf("Init UDP server at address: "); address.print();
+	logf("Init UDP server at address: "); address.print();
 	if (remoteTcpAddress.port)
-		{ printf(", with remote TCP address: "); remoteTcpAddress.print(); }
-	printf("\n");
+		{ logf(", with remote TCP address: "); remoteTcpAddress.print(); }
+	logf("\n");
 	
 	if (!crypt.setKey(key))
-		{ printf("bad key, cancelled\n"); return false; }
+		{ logf("bad key, cancelled\n"); return false; }
 	
 	udpSockId = Socket::udpBind(address);
 	if (udpSockId < 0)
-		{ crypt.resetKey(); printf("cannot bind, cancelled\n"); return false; }
+		{ crypt.resetKey(); logf("cannot bind, cancelled\n"); return false; }
 	
-	printf("success\n");
+	logf("success\n");
 	this->remoteTcpAddress = remoteTcpAddress;
 	return true;
 }
@@ -64,16 +64,16 @@ bool Tunnel::initUdpServer(const Address &address, const Address &remoteTcpAddre
 
 bool Tunnel::initTcpServer(const Address &address, const Address &remoteUdpAddress) {
 	closeTcpServer();
-	printf("Init TCP server at address: "); address.print(); printf("\n");
+	logf("Init TCP server at address: "); address.print(); logf("\n");
 	
 	if (udpSockId < 0)
-		{ printf("UDP server was not initialized, cancelled\n"); return false; }
+		{ logf("UDP server was not initialized, cancelled\n"); return false; }
 	
 	tcpSockId = Socket::tcpListen(address);
 	if (tcpSockId < 0)
-		{ printf("cannot listen, cancelled\n"); return false; }
+		{ logf("cannot listen, cancelled\n"); return false; }
 	
-	printf("success\n");
+	logf("success\n");
 	this->remoteUdpAddress = remoteUdpAddress;
 	return true;
 }
@@ -83,7 +83,7 @@ void Tunnel::closeUdpServer() {
 	if (udpSockId < 0) return;
 	closeTcpServer();
 	
-	printf("Close UDP server\n");
+	logf("Close UDP server\n");
 	for(ConnMap::iterator i = connections.begin(); i != connections.end(); ++i)
 		Socket::close(i->second.tcpSockId);
 	connections.clear();
@@ -97,7 +97,7 @@ void Tunnel::closeUdpServer() {
 
 void Tunnel::closeTcpServer() {
 	if (tcpSockId < 0) return;
-	printf("Close TCP server\n");
+	logf("Close TCP server\n");
 	Socket::close(tcpSockId);
 	tcpSockId = -1;
 	remoteUdpAddress = Address();
@@ -140,12 +140,12 @@ bool Tunnel::recvUdpPacket() {
 	id.id = packet.connId;
 	ConnMap::iterator i = connections.find(id);
 	if (i == connections.end() && cmd == CMD_DATA && remoteTcpAddress.port && !closedConnections.count(id)) {
-		printf("Open incoming connection from UDP: ");
+		logf("Open incoming connection from UDP: ");
 		id.address.print();
-		printf(", id: %u\n", id.id);
+		logf(", id: %u\n", id.id);
 		int sockId = Socket::tcpConnect(remoteTcpAddress);
 		if (sockId < 0) {
-			printf("cannot init TCP connection, cancelled\n");
+			logf("cannot init TCP connection, cancelled\n");
 		} else {
 			i = connections.emplace(id, Connection::Args(*this, id, sockId)).first;
 		}
@@ -241,9 +241,9 @@ bool Tunnel::iteration() {
 	
 	if (poll.list[0].closed || (tcpSockId >= 0 && poll.list[1].closed)) {
 		if (poll.list[0].closed)
-			printf("UDP socket closed\n");
+			logf("UDP socket closed\n");
 		if (tcpSockId >= 0 && poll.list[1].closed)
-			printf("TCP server socket closed\n");
+			logf("TCP server socket closed\n");
 		poll.list.clear();
 		close();
 		return false;
@@ -261,9 +261,9 @@ bool Tunnel::iteration() {
 			ConnId id;
 			id.address = remoteUdpAddress;
 			id.id = crypt.random();
-			printf("Open incoming connection from TCP: ");
+			logf("Open incoming connection from TCP: ");
 			address.print();
-			printf(", id: %u\n", id.id);
+			logf(", id: %u\n", id.id);
 			Connection &conn = connections.emplace(id, Connection::Args(*this, id, sockId)).first->second;
 			conn.tcpRecvQueue.readFromTcp();
 		}
@@ -324,7 +324,7 @@ bool Tunnel::iteration() {
 			DebugMsg("%u, inactivate tcp", conn.id.id);
 			Socket::close(conn.tcpSockId);
 			conn.tcpSockId = -1;
-			printf("Close connection, id: %u\n", conn.id.id);
+			logf("Close connection, id: %u\n", conn.id.id);
 			closedConnections[conn.id] = time + 2*udpSilenceDuration;
 			connections.erase(j);
 			continue;
@@ -334,14 +334,14 @@ bool Tunnel::iteration() {
 			DebugMsg("%u, inactivate udp, all data sent", conn.id.id);
 			conn.udpActive = false;
 			termQueue.insert(conn.id);
-			printf("Close connection, id: %u\n", conn.id.id);
+			logf("Close connection, id: %u\n", conn.id.id);
 			closedConnections[conn.id] = time + 2*udpSilenceDuration;
 			connections.erase(j);
 			continue;
 		}
 		
 		if (!conn.udpActive && conn.tcpSockId < 0) {
-			printf("Close connection, id: %u\n", conn.id.id);
+			logf("Close connection, id: %u\n", conn.id.id);
 			closedConnections[conn.id] = time + 2*udpSilenceDuration;
 			connections.erase(j);
 			continue;