diff --git a/Check/Check.pro b/Check/Check.pro
index 1683211..b2fec1f 100644
--- a/Check/Check.pro
+++ b/Check/Check.pro
@@ -1,6 +1,6 @@
 QT += core
 
-TARGET = check_update
+TARGET = ATBUpdateCheck
 
 VERSION="1.0.0"
 win32 {
@@ -63,9 +63,13 @@ contains( CONFIG, DesktopLinux ) {
 }
 
 SOURCES += \
-        main.cpp
+        main.cpp \
+        ismas_client.cpp \
+        message_handler.cpp
 
-# HEADERS += \
+HEADERS += \
+        ismas_client.h \
+        message_handler.h
 
 ##########################################################################################
 # for running program on target through QtCreator
diff --git a/Check/ismas_client.cpp b/Check/ismas_client.cpp
new file mode 100644
index 0000000..ae34314
--- /dev/null
+++ b/Check/ismas_client.cpp
@@ -0,0 +1,364 @@
+#ifdef __WIN32__
+#error "WIN32 NOT SUPPORTED"
+#else
+
+#include "ismas_client.h"
+
+#include <cstring>
+#include <cstdio>
+
+#include <errno.h>
+#include <arpa/inet.h> // inet_addr()
+#include <netdb.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <netinet/in.h>
+#include <netinet/tcp.h>
+#include <string.h>
+#include <strings.h> // bzero()
+#include <sys/socket.h>
+#include <unistd.h> // read(), write(), close()
+#include <fcntl.h>
+
+
+#include <QThread>
+#include <QJsonDocument>
+#include <QJsonObject>
+
+#if 0
+########################
+# Spec vom 27.10.2023:
+# U0010 -> %-Werte
+# U0001 -> 100%
+# U0003 -> "FAIL"
+# U0002 -> "" (OK -> WAIT state reset)
+# ISMAS -> "WAIT"
+########################
+#
+# $1: EVENT: U0001 update finished: 100%
+#            U0002 reset TRG
+#            U0003 error
+#            U0010 for update process
+# $2: PERCENT : "only for ISMAS: 0-100%",
+# $3: RESULTCODE : "only for ISMAS",
+#   0: Success
+#   1: no Update nessesary
+#   2: Backup failed
+#   3: Package error/ Wrong package
+#   4: Install Error
+# $4: STEP : "running step (only for us): update_psa...",
+# $5: STEP_RESULT : "error and result text",
+# $6: VERSION : "opkg and conf info; what will be updated"
+#
+#endif
+
+#include <QDateTime>
+#include <QDebug>
+
+void IsmasClient::printDebugMessage(int port,
+                                    QString const &clientIP,
+                                    int clientPort,
+                                    QString const &message) {
+#if 0
+    Q_UNUSED(port);
+    Q_UNUSED(clientIP);
+    Q_UNUSED(clientPort);
+    Q_UNUSED(message);
+#else
+    qDebug().noquote()
+        << "\n"
+        << "SEND-REQUEST-RECEIVE-RESPONSE ..." << "\n"
+        << "hostname ........" << "127.0.0.1"  << "\n"
+        << "port ............" << port << "\n"
+        << "local address ..." << clientIP << "\n"
+        << "local port ......" << clientPort << "\n"
+        << message;
+#endif
+}
+
+void IsmasClient::printInfoMessage(int port,
+                                   QString const &clientIP,
+                                   int clientPort,
+                                   QString const &message) {
+#if 0
+    Q_UNUSED(port);
+    Q_UNUSED(clientIP);
+    Q_UNUSED(clientPort);
+    Q_UNUSED(message);
+#else
+    qInfo().noquote()
+        << "\n"
+        << "SEND-REQUEST-RECEIVE-RESPONSE ..." << "\n"
+        << "hostname ........" << "127.0.0.1"  << "\n"
+        << "port ............" << port << "\n"
+        << "local address ..." << clientIP << "\n"
+        << "local port ......" << clientPort << "\n"
+        << message;
+#endif
+}
+
+void IsmasClient::printErrorMessage(int port,
+                                    QString const &clientIP,
+                                    int clientPort,
+                                    QString const &message) {
+    qCritical().noquote()
+        << "\n"
+        << "SEND-REQUEST-RECEIVE-RESPONSE ..." << "\n"
+        << "hostname ........" << "127.0.0.1"  << "\n"
+        << "port ............" << port << "\n"
+        << "local address ..." << clientIP << "\n"
+        << "local port ......" << clientPort << "\n"
+        << message;
+}
+
+std::optional<QString>
+IsmasClient::sendRequestReceiveResponse(int port, QString const &request) {
+
+    qInfo() << "REQUEST" << request;
+
+    int sockfd;
+    int r;
+    errno = 0;
+    // socket create and verification
+    if ((sockfd = ::socket(AF_INET, SOCK_STREAM, 0)) == -1) {
+        qCritical().noquote()
+            << "\n"
+            << "SEND-REQUEST-RECEIVE-RESPONSE ..." << "\n"
+            << "SOCKET CREATION FAILED (" << strerror(errno) << ")";
+        return std::nullopt;
+    }
+
+    struct sockaddr_in servAddr;
+    bzero(&servAddr, sizeof(servAddr));
+    // assign IP, PORT
+    servAddr.sin_family = AF_INET;
+    servAddr.sin_addr.s_addr = inet_addr("127.0.0.1");
+
+    servAddr.sin_port = htons(port);
+    // connect the client socket to server socket
+    if ((r = ::connect(sockfd, (struct sockaddr *)(&servAddr), sizeof(servAddr))) != 0) {
+        qCritical().noquote()
+            << "\n"
+            << "SEND-REQUEST-RECEIVE-RESPONSE ..." << "\n"
+            << "CONNECTION WITH SERVER FAILED (" << strerror(r) << ")";
+        ::close(sockfd);
+        return std::nullopt;
+    }
+
+    struct sockaddr_in clientAddr;
+    bzero(&clientAddr, sizeof(clientAddr));
+    socklen_t sockLen = sizeof(clientAddr);
+
+    char clientIP[16];
+    bzero(&clientIP, sizeof(clientIP));
+    getsockname(sockfd, (struct sockaddr *)(&clientAddr), &sockLen);
+    inet_ntop(AF_INET, &clientAddr.sin_addr, clientIP, sizeof(clientIP));
+    unsigned int clientPort = ntohs(clientAddr.sin_port);
+
+    printDebugMessage(port, clientIP, clientPort, QString("CONNECTED TO SERVER"));
+
+    struct timeval tv;
+    tv.tv_sec = 10;  /* 10 secs timeout for read and write */
+
+    struct linger so_linger;
+    so_linger.l_onoff = 1;
+    so_linger.l_linger = 0;
+
+    int maxfdp1;
+    fd_set rset;
+    fd_set wset;
+
+    setsockopt(sockfd, SOL_SOCKET, SO_LINGER, &so_linger, sizeof(so_linger));
+    // no reliable, but does not harm, as we use select() as well
+    setsockopt(sockfd, SOL_SOCKET, SO_SNDTIMEO, &tv, sizeof(tv));
+    setsockopt(sockfd, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv));
+    int flag = 1;
+    setsockopt(sockfd, IPPROTO_TCP, TCP_NODELAY, (char *) &flag, sizeof(int));
+
+    static char buf[1024*8];
+    bzero(buf, sizeof(buf));
+    int const bytesToWrite = strlen(request.toStdString().c_str());
+    strncpy(buf, request.toStdString().c_str(), sizeof(buf)-1);
+
+    int loop = 0;
+    int bytesWritten = 0;
+    while (bytesWritten < bytesToWrite) {
+        errno = 0;
+        FD_ZERO(&wset);
+        FD_SET(sockfd, &wset);
+        maxfdp1 = sockfd + 1;
+        tv.tv_sec = 60;  /* 60 secs timeout for read and write -> APISM cuts the connection after 30s */
+        tv.tv_usec = 0;
+
+        int const w = select(maxfdp1, NULL, &wset, NULL, &tv);
+        if (w < 0) { // error
+            if (errno == EINTR) {
+                printErrorMessage(port, clientIP, clientPort,
+                    QString("INTERRUPTED BY SIGNAL (1) (") + strerror(errno) + ")");
+                continue;
+            } else {
+                printErrorMessage(port, clientIP, clientPort,
+                        QString("SELECT-ERROR (WRITE) %1(").arg(loop) + strerror(errno) + ")");
+                ::close(sockfd);
+                return std::nullopt;
+            }
+        } else
+        if (w == 0) { // timeout
+            printErrorMessage(port, clientIP, clientPort,
+                    QString("SELECT-TIMEOUT (WRITE) %1(").arg(loop) + strerror(errno) + ")");
+            if (++loop < 10) {
+                QThread::msleep(500);
+                continue;
+            }
+            ::close(sockfd);
+            return std::nullopt;
+        } else
+        if (w > 0) {
+            int n = ::sendto(sockfd, buf+bytesWritten, bytesToWrite-bytesWritten, 0, NULL, 0);
+            if (n >= 0) {
+                bytesWritten += n;
+            } else {
+                if (errno == EWOULDBLOCK) {
+                    if (++loop < 10) {
+                        QThread::msleep(500);
+                        continue;
+                    }
+                    printErrorMessage(port, clientIP, clientPort,
+                        QString("WRITE TIMEOUT %1(").arg(loop) + strerror(errno) + ")");
+                    ::close(sockfd);
+                    return std::nullopt;
+                } else
+                if (errno == EINTR) {
+                    printErrorMessage(port, clientIP, clientPort,
+                        QString("WRITE INTERRUPTED BY SIGNAL (1) (") + strerror(errno) + ")");
+                    continue;
+                }
+            }
+        }
+    }
+
+    // DO NOT USE SHUTDOWN! APISM CAN NOT COPE WITH IT
+    // errno = 0;
+    // if (shutdown(sockfd, SHUT_WR) < 0) {
+    //     printErrorMessage(port, clientIP, clientPort,
+    //        QString("CANNOT CLOSE WRITING END (") + strerror(errno) + ")");
+    // }
+
+    printInfoMessage(port, clientIP, clientPort, QString("MESSAGE SENT <<<") + buf + ">>>");
+
+    loop = 0;
+    bzero(buf, sizeof(buf));
+    int bytesToRead = sizeof(buf)-1;
+    int bytesRead = 0;
+    while (bytesRead < bytesToRead) {
+        errno = 0;
+        FD_ZERO(&rset);
+        FD_SET(sockfd, &rset);
+        maxfdp1 = sockfd + 1;
+        tv.tv_sec = 60;  /* 60 secs timeout for read and write */
+        tv.tv_usec = 0;
+
+        QString const selectStart = QDateTime::currentDateTime().toString(Qt::ISODateWithMs);
+
+        int const r = select(maxfdp1, &rset, NULL, NULL, &tv);
+        if (r < 0) { // error
+            if (errno == EINTR) {
+                printErrorMessage(port, clientIP, clientPort,
+                    QString("INTERRUPTED BY SIGNAL (2) (") + strerror(errno) + ")");
+                continue;
+            } else {
+                printErrorMessage(port, clientIP, clientPort,
+                        QString("SELECT-ERROR (READ) %1(").arg(loop) + strerror(errno) + ")");
+                ::close(sockfd);
+                return std::nullopt;
+            }
+        } else
+        if (r == 0) { // timeout
+            printErrorMessage(port, clientIP, clientPort,
+                    QString("SELECT-TIMEOUT (READ) %1(").arg(loop) + strerror(errno) + ")");
+            if (++loop < 10) {
+                QThread::msleep(500);
+                continue;
+            }
+            ::close(sockfd);
+            return std::nullopt;
+        } else
+        if (r > 0) {
+            if (FD_ISSET(sockfd, &rset)) {
+                int n = ::recvfrom(sockfd, buf+bytesRead, bytesToRead-bytesRead,
+                                   0, NULL, NULL);
+                if (n > 0) { //
+                    bytesRead += n;
+                } else
+                if (n == 0) {
+                    // The return value will be 0 when the peer has performed an orderly shutdown.
+                    printErrorMessage(port, clientIP, clientPort,
+                        QString("PEER CLOSED CONNECTION (") + strerror(errno) + ") START AT" +
+                                selectStart + " NOW " + QDateTime::currentDateTime().toString(Qt::ISODateWithMs));
+                    ::close(sockfd);
+                    return std::nullopt;
+                } else
+                if (n < 0) {
+                    if (errno == EWOULDBLOCK) { // check just in case
+                        if (++loop < 10) {
+                            QThread::msleep(500);
+                            continue;
+                        }
+                        printErrorMessage(port, clientIP, clientPort,
+                                QString("READ TIMEOUT %1(").arg(loop) + strerror(errno) + ")");
+                        ::close(sockfd);
+                        return std::nullopt;
+                    }
+                    if (errno == EINTR) {
+                        printErrorMessage(port, clientIP, clientPort,
+                            QString("INTERRUPTED BY SIGNAL (2) (") + strerror(errno) + ")");
+                        continue;
+                    }
+                }
+            }
+        }
+
+        // printInfoMessage(port, clientIP, clientPort, QString("MESSAGE RECEIVED ") + buf);
+        QString response(buf);
+
+        if (int idx = response.indexOf("{\"error\":\"ISMAS is offline\"}")) {
+            response = response.mid(0, idx);
+        } else
+        if (response.contains("RECORD")) { // RECORD SAVED or RECORD WRITE ABORTED
+            printInfoMessage(port, clientIP, clientPort, QString("IGNORED '") + response + "' RESPONSE");
+            ::close(sockfd);
+            return std::nullopt;
+        }
+
+        QJsonParseError parseError;
+        QJsonDocument document(QJsonDocument::fromJson(response.toUtf8(), &parseError));
+        if (parseError.error == QJsonParseError::NoError) {
+            if (document.isObject()) { // done: received valid APISM response
+                printInfoMessage(port, clientIP, clientPort,
+                   QString("VALID APISM RESPONSE .. \n") + response);
+                ::close(sockfd);
+                return response;
+            } else {
+                printInfoMessage(port, clientIP, clientPort,
+                   QString("CORRUPTED RESPONSE ") + response);
+                ::close(sockfd);
+                return std::nullopt;
+            }
+        } else {
+            if (!response.contains("RECORD")) {
+                // maybe APISM does not send valid JSON: "RECORD SAVED" etc.
+                printDebugMessage(port, clientIP, clientPort,
+                    QString("PARSE ERROR ") + response + " " + parseError.errorString());
+            }
+            ::close(sockfd);
+            return std::nullopt;
+        }
+    }
+    return std::nullopt;
+}
+
+char const *IsmasClient::reason[REASON::ENTRIES] = {
+    "TIME-TRIGGERED", "SERVICE", "DEV-TEST"
+};
+
+#endif // __WIN32__
diff --git a/Check/ismas_client.h b/Check/ismas_client.h
new file mode 100644
index 0000000..4c38c78
--- /dev/null
+++ b/Check/ismas_client.h
@@ -0,0 +1,51 @@
+#ifndef ISMAS_CLIENT_H_INCLUDED
+#define ISMAS_CLIENT_H_INCLUDED
+
+#include <QObject>
+#include <QString>
+#include <optional>
+
+class IsmasClient : public QObject {
+    Q_OBJECT
+
+public:
+    explicit IsmasClient()  = default;
+
+    enum APISM {
+        DB_PORT = 7777,
+        DIRECT_PORT = 7778
+    };
+
+    enum RESULT_CODE {
+        SUCCESS=0,
+        // if between 00:00 - 04:00 Wait-button state not WAIT, then we assume
+        // that's an automatic nightly (not-necessary) update
+        NO_UPDATE_NECESSARY=1,
+        // if APISM reports the ISMAS is not available (15x, 6s delay each)
+        ISMAS_NO_CONNECTION_ERROR=2,
+        // if not within 00:00-04:00 and WAIT-button was not in state WAIT
+        ISMAS_TRIGGER_ERROR=3,
+    };
+
+    enum REASON {
+        TIME_TRIGGERED = 0,
+        SERVICE,
+        DEV_TEST,
+        ENTRIES
+    };
+
+    static char const *reason[REASON::ENTRIES];
+
+    static std::optional<QString>
+        sendRequestReceiveResponse(int port, QString const &request);
+
+  private:
+    static void printDebugMessage(int port, QString const &clientIP, int clientPort,
+                                  QString const &message);
+    static void printInfoMessage(int port, QString const &clientIP, int clientPort,
+                                 QString const &message);
+    static void printErrorMessage(int port, QString const &clientIP, int clientPort,
+                                  QString const &message);
+};
+
+#endif // ISMAS_CLIENT_H_INCLUDED
diff --git a/Check/main.cpp b/Check/main.cpp
index 627d253..b670f3b 100644
--- a/Check/main.cpp
+++ b/Check/main.cpp
@@ -9,6 +9,43 @@
 #include <QDir>
 #include <QDebug>
 
+#include "commandline_parser.h"
+#include "message_handler.h"
+
 int main(int argc, char **argv) {
+    QByteArray const value = qgetenv("LC_ALL");
+    if (value.isEmpty() || value != "C") {
+        qputenv("LC_ALL", "C");
+    }
+
+
+    // qputenv("XDG_RUNTIME_DIR", "/var/run/user/0");
+
+    openlog("ATB-UPDATE_CHECK", LOG_PERROR | LOG_PID | LOG_CONS, LOG_USER);
+
+    QCoreApplication a(argc, argv);
+    QCoreApplication::setApplicationName("ATBUpdateCheck");
+    QCoreApplication::setApplicationVersion(APP_VERSION);
+
+    if (!messageHandlerInstalled()) { // change internal qt-QDebug-handling
+        atbInstallMessageHandler(nullptr);
+        //atbInstallMessageHandler(atbDebugOutput);
+        setDebugLevel(LOG_NOTICE);
+    }
+
+    QCommandLineParser parser;
+    QCommandLineOption ismasConnectOption("ismas-connected");
+    QCommandLineOption updateRequestedOption("update-requested");
+    parser.addOption(ismasConnectOption);
+    parser.addOption(updateRequestedOption);
+    parser.process(a);
+
+    if (parser.isSet(ismasConnectOption)) {
+        qCritical() << parser.isSet(ismasConnectOption);
+    } else
+    if (parser.isSet(updateRequestedOption)) {
+        qCritical() << parser.isSet(updateRequestedOption);
+    }
+
     return 0;
 }
diff --git a/Check/message_handler.cpp b/Check/message_handler.cpp
new file mode 100755
index 0000000..996bd2f
--- /dev/null
+++ b/Check/message_handler.cpp
@@ -0,0 +1,97 @@
+#include "message_handler.h"
+
+#include <QDateTime>
+#include <cstring>
+#include <QString>
+#include <QFileInfo>
+#include <QMessageLogContext>
+
+
+static char const *DBG_NAME[] = { "DBG  ", "WARN ", "CRIT ", "FATAL", "INFO " };
+static bool installedMsgHandler = false;
+static int debugLevel = LOG_NOTICE;
+
+int getDebugLevel() { return debugLevel; }
+void setDebugLevel(int newDebugLevel) {
+    debugLevel = newDebugLevel;
+}
+
+bool messageHandlerInstalled() {
+    return installedMsgHandler;
+}
+
+QtMessageHandler atbInstallMessageHandler(QtMessageHandler handler) {
+    installedMsgHandler = (handler != 0);
+    static QtMessageHandler prevHandler = nullptr;
+    if (handler) {
+        prevHandler = qInstallMessageHandler(handler);
+        return prevHandler;
+    } else {
+        return qInstallMessageHandler(prevHandler);
+    }
+}
+
+///
+/// \brief Print message according to given debug level.
+///
+/// \note Install this function using qInstallMsgHandler().
+///
+///  int main(int argc, char **argv) {
+///     installMsgHandler(atbDebugOutput);
+///     QApplication app(argc, argv);
+///     ...
+///     return app.exec();
+///  }
+///
+#if (QT_VERSION > QT_VERSION_CHECK(5, 0, 0) && QT_VERSION < QT_VERSION_CHECK(6, 0, 0))
+void atbDebugOutput(QtMsgType type, const QMessageLogContext &context, const QString &msg) {
+    Q_UNUSED(context);
+    QString const localMsg = QString(DBG_NAME[type]) + msg.toLocal8Bit();
+
+    switch (debugLevel) {
+        case LOG_DEBUG: { // debug-level message
+            syslog(LOG_DEBUG, "%s", localMsg.toStdString().c_str());
+        } break;
+        case LOG_INFO: { // informational message
+            if (type != QtDebugMsg) {
+                syslog(LOG_DEBUG, "%s", localMsg.toStdString().c_str());
+            }
+        } break;
+        case LOG_NOTICE: { // normal, but significant, condition
+            if (type != QtDebugMsg) {
+                syslog(LOG_DEBUG, "%s", localMsg.toStdString().c_str());
+            }
+        } break;
+        case LOG_WARNING: { // warning conditions
+            if (type != QtInfoMsg && type != QtDebugMsg) {
+                syslog(LOG_DEBUG, "%s", localMsg.toStdString().c_str());
+            }
+        } break;
+        case LOG_ERR: { // error conditions
+            if (type != QtInfoMsg && type != QtDebugMsg && type != QtWarningMsg) {
+                syslog(LOG_DEBUG, "%s", localMsg.toStdString().c_str());
+            }
+        } break;
+        case LOG_CRIT: { // critical conditions
+            if (type != QtInfoMsg && type != QtDebugMsg && type != QtWarningMsg) {
+                syslog(LOG_DEBUG, "%s", localMsg.toStdString().c_str());
+            }
+        } break;
+        case LOG_ALERT: { // action must be taken immediately
+            if (type != QtInfoMsg && type != QtDebugMsg && type != QtWarningMsg) {
+                syslog(LOG_DEBUG, "%s", localMsg.toStdString().c_str());
+            }
+        } break;
+        case LOG_EMERG: { // system is unusable
+            if (type != QtInfoMsg && type != QtDebugMsg && type != QtWarningMsg) {
+                syslog(LOG_DEBUG, "%s", localMsg.toStdString().c_str());
+            }
+        } break;
+        default: {
+            //fprintf(stderr, "%s No ErrorLevel defined! %s\n",
+            //    datetime.toStdString().c_str(), msg.toStdString().c_str());
+        }
+    }
+}
+#endif
+
diff --git a/Check/message_handler.h b/Check/message_handler.h
new file mode 100755
index 0000000..98c4d7e
--- /dev/null
+++ b/Check/message_handler.h
@@ -0,0 +1,23 @@
+#ifndef MESSAGE_HANDLER_H_INCLUDED
+#define MESSAGE_HANDLER_H_INCLUDED
+
+#include <QtGlobal>
+#ifdef __linux__
+#include <syslog.h>
+#endif
+
+int getDebugLevel();
+void setDebugLevel(int newDebugLevel);
+
+bool messageHandlerInstalled();
+QtMessageHandler atbInstallMessageHandler(QtMessageHandler handler);
+
+#if QT_VERSION < QT_VERSION_CHECK(5, 0, 0)
+// typedef void (*QtMessageHandler)(QtMsgType, const char *);
+void atbDebugOutput(QtMsgType type, const char *msg);
+#elif QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
+// typedef void (*QtMessageHandler)(QtMsgType, const QMessageLogContext &, const QString &);
+void atbDebugOutput(QtMsgType type, const QMessageLogContext &context, const QString &msg);
+#endif
+
+#endif // MESSAGE_HANDLER_H_INCLUDED