You can disable the automatic update check by setting CRYFS_NO_UPDATE_CHECK=true in your environment.

ChangeLog.txt

@@ -3,6 +3,7 @@ Version 0.9.3 (unreleased)
 * It's easier for tools and scripts to use CryFS:
   If an environment variable CRYFS_FRONTEND=noninteractive is set, we don't ask for options (but take default values for everything that's not specified on command line).
   Furthermore, we won't ask for password confirmation when creating a file system but the password only has to be sent once to stdin.
+* You can disable the automatic update check by setting CRYFS_NO_UPDATE_CHECK=true in your environment.
 
 Version 0.9.2
 ---------------

src/cryfs/CMakeLists.txt

@@ -5,6 +5,7 @@ set(SOURCES
     cli/VersionChecker.cpp
     cli/VersionCompare.cpp
     cli/CallAfterTimeout.cpp
+    cli/Environment.cpp
     cli/program_options/utils.cpp
     cli/program_options/ProgramOptions.cpp
     cli/program_options/Parser.cpp

src/cryfs/cli/Cli.cpp

@@ -22,6 +22,7 @@
 
 #include "VersionChecker.h"
 #include "VersionCompare.h"
+#include "Environment.h"
 
 //TODO Fails with gpg-homedir in filesystem: gpg --homedir gpg-homedir --gen-key
 //TODO Many functions accessing the ProgramOptions object. Factor out into class that stores it as a member.
@@ -70,15 +71,10 @@ using cpputils::dynamic_pointer_move;
 //TODO Performance difference when setting compiler parameter -maes for scrypt?
 
 namespace cryfs {
-    const string Cli::CRYFS_FRONTEND_KEY = "CRYFS_FRONTEND";
-    const string Cli::CRYFS_FRONTEND_NONINTERACTIVE = "noninteractive";
 
     Cli::Cli(RandomGenerator &keyGenerator, const SCryptSettings &scryptSettings, shared_ptr<Console> console, shared_ptr<HttpClient> httpClient):
             _keyGenerator(keyGenerator), _scryptSettings(scryptSettings), _console(console), _httpClient(httpClient), _noninteractive(false) {
-        char *frontend = std::getenv(CRYFS_FRONTEND_KEY.c_str());
+        _noninteractive = Environment::isNoninteractive();
-        if (frontend != nullptr && frontend == CRYFS_FRONTEND_NONINTERACTIVE) {
-            _noninteractive = true;
-        }
     }
 
     void Cli::_showVersion() {
@@ -95,6 +91,13 @@ namespace cryfs {
 #ifndef NDEBUG
         cout << "WARNING! This is a debug build. Performance might be slow." << endl;
 #endif
+        if (!Environment::noUpdateCheck()) {
+            _checkForUpdates();
+        }
+        cout << endl;
+    }
+
+    void Cli::_checkForUpdates() {
         VersionChecker versionChecker(_httpClient);
         optional<string> newestVersion = versionChecker.newestVersion();
         if (newestVersion == none) {
@@ -106,7 +109,6 @@ namespace cryfs {
         if (securityWarning != none) {
             cout << *securityWarning << endl;
         }
-        cout << endl;
     }
 
     bool Cli::_checkPassword(const string &password) {

src/cryfs/cli/Cli.h

@@ -19,6 +19,7 @@ namespace cryfs {
         int main(int argc, char *argv[]);
 
     private:
+        void _checkForUpdates();
         void _runFilesystem(const program_options::ProgramOptions &options);
         CryConfigFile _loadOrCreateConfig(const program_options::ProgramOptions &options);
         boost::optional<CryConfigFile> _loadOrCreateConfigFile(const boost::filesystem::path &configFilePath, const boost::optional<std::string> &cipher);
@@ -40,8 +41,6 @@ namespace cryfs {
         boost::optional<cpputils::unique_ref<CallAfterTimeout>> _createIdleCallback(boost::optional<double> minutes, std::function<void()> callback);
         void _sanityCheckFilesystem(CryDevice *device);
 
-        static const std::string CRYFS_FRONTEND_KEY;
-        static const std::string CRYFS_FRONTEND_NONINTERACTIVE;
 
         cpputils::RandomGenerator &_keyGenerator;
         cpputils::SCryptSettings _scryptSettings;

src/cryfs/cli/Environment.cpp

@@ -0,0 +1,19 @@
+#include "Environment.h"
+#include <cstdlib>
+
+using std::string;
+
+namespace cryfs {
+    const string Environment::FRONTEND_KEY = "CRYFS_FRONTEND";
+    const string Environment::FRONTEND_NONINTERACTIVE = "noninteractive";
+    const string Environment::NOUPDATECHECK_KEY = "CRYFS_NO_UPDATE_CHECK";
+
+    bool Environment::isNoninteractive() {
+        char *frontend = std::getenv(FRONTEND_KEY.c_str());
+        return frontend != nullptr && frontend == FRONTEND_NONINTERACTIVE;
+    }
+
+    bool Environment::noUpdateCheck() {
+        return nullptr != std::getenv(NOUPDATECHECK_KEY.c_str());
+    }
+}

src/cryfs/cli/Environment.h

@@ -0,0 +1,24 @@
+#pragma once
+#ifndef MESSMER_CRYFS_CLI_ENVIRONMENT_H
+#define MESSMER_CRYFS_CLI_ENVIRONMENT_H
+
+#include <string>
+
+namespace cryfs {
+
+    class Environment {
+    public:
+        static bool isNoninteractive();
+        static bool noUpdateCheck();
+
+    private:
+        Environment() = delete;
+
+        static const std::string FRONTEND_KEY;
+        static const std::string FRONTEND_NONINTERACTIVE;
+        static const std::string NOUPDATECHECK_KEY;
+    };
+
+}
+
+#endif

test/cryfs/CMakeLists.txt

@@ -9,6 +9,7 @@ set(SOURCES
     cli/program_options/ProgramOptionsTest.cpp
     cli/program_options/ParserTest.cpp
     cli/CliTest_ShowingHelp.cpp
+    cli/EnvironmentTest.cpp
     cli/VersionCheckerTest.cpp
     cli/VersionCompareTest.cpp
     config/crypto/CryConfigEncryptorFactoryTest.cpp

test/cryfs/cli/EnvironmentTest.cpp

@@ -0,0 +1,64 @@
+#include <gtest/gtest.h>
+#include <cryfs/cli/Environment.h>
+#include <boost/optional.hpp>
+
+using namespace cryfs;
+using std::string;
+using boost::optional;
+using boost::none;
+
+class EnvironmentTest : public ::testing::Test {
+public:
+    // WithEnv sets an environment variable while it is in scope.
+    // Once it leaves scope, the environment is reset.
+    class WithEnv {
+    public:
+        WithEnv(const string &key, const string &value): _key(key) , _oldValue(none) {
+            char *oldValue = std::getenv(key.c_str());
+            if (nullptr != oldValue) {
+                _oldValue = string(oldValue);
+            }
+            ::setenv(key.c_str(), value.c_str(), 1);
+        }
+        ~WithEnv() {
+            if (none == _oldValue) {
+                ::unsetenv(_key.c_str());
+            } else {
+                ::setenv(_key.c_str(), _oldValue->c_str(), 1);
+            }
+        }
+
+    private:
+        string _key;
+        optional<string> _oldValue;
+    };
+};
+
+TEST_F(EnvironmentTest, Noninteractive_Unset) {
+    EXPECT_FALSE(Environment::isNoninteractive());
+}
+
+TEST_F(EnvironmentTest, Noninteractive_Set) {
+    WithEnv env("CRYFS_FRONTEND", "noninteractive");
+    EXPECT_TRUE(Environment::isNoninteractive());
+}
+
+TEST_F(EnvironmentTest, Noninteractive_SetToOtherValue) {
+    WithEnv env("CRYFS_FRONTEND", "someotherfrontend");
+    EXPECT_FALSE(Environment::isNoninteractive());
+}
+
+TEST_F(EnvironmentTest, NoUpdateCheck_Unset) {
+    EXPECT_FALSE(Environment::noUpdateCheck());
+}
+
+TEST_F(EnvironmentTest, NoUpdateCheck_Set) {
+    WithEnv env("CRYFS_NO_UPDATE_CHECK", "true");
+    EXPECT_TRUE(Environment::noUpdateCheck());
+}
+
+TEST_F(EnvironmentTest, NoUpdateCheck_SetToOtherValue) {
+    WithEnv env("CRYFS_NO_UPDATE_CHECK", "someothervalue");
+    // No matter what the value is, setting the environment variable says we don't do update checks.
+    EXPECT_TRUE(Environment::noUpdateCheck());
+}