https://github.com/google/mozc/issues/470

--- /src/base/system_util.cc
+++ /src/base/system_util.cc
@@ -208,28 +208,39 @@
   dir_ = "/";
   return;
 #else  // MOZC_USE_PEPPER_FILE_IO
+  const char *configuration_directory_env;
   string dir;
 
 #ifdef OS_WIN
-  DCHECK(SUCCEEDED(Singleton<LocalAppDataDirectoryCache>::get()->result()));
-  dir = Singleton<LocalAppDataDirectoryCache>::get()->path();
+  configuration_directory_env = ::getenv("MOZC_CONFIGURATION_DIRECTORY");
+  if (configuration_directory_env) {
+    dir = configuration_directory_env;
+  } else {
+    DCHECK(SUCCEEDED(Singleton<LocalAppDataDirectoryCache>::get()->result()));
+    dir = Singleton<LocalAppDataDirectoryCache>::get()->path();
 #ifdef GOOGLE_JAPANESE_INPUT_BUILD
-  dir = FileUtil::JoinPath(dir, kCompanyNameInEnglish);
-  FileUtil::CreateDirectory(dir);
+    dir = FileUtil::JoinPath(dir, kCompanyNameInEnglish);
+    FileUtil::CreateDirectory(dir);
 #endif  // GOOGLE_JAPANESE_INPUT_BUILD
-  dir = FileUtil::JoinPath(dir, kProductNameInEnglish);
+    dir = FileUtil::JoinPath(dir, kProductNameInEnglish);
+  }
 
 #elif defined(OS_MACOSX)
-  dir = MacUtil::GetApplicationSupportDirectory();
+  configuration_directory_env = ::getenv("MOZC_CONFIGURATION_DIRECTORY");
+  if (configuration_directory_env) {
+    dir = configuration_directory_env;
+  } else {
+    dir = MacUtil::GetApplicationSupportDirectory();
 #ifdef GOOGLE_JAPANESE_INPUT_BUILD
-  dir = FileUtil::JoinPath(dir, "Google");
-  // The permission of ~/Library/Application Support/Google seems to be 0755.
-  // TODO(komatsu): nice to make a wrapper function.
-  ::mkdir(dir.c_str(), 0755);
-  dir = FileUtil::JoinPath(dir, "JapaneseInput");
+    dir = FileUtil::JoinPath(dir, "Google");
+    // The permission of ~/Library/Application Support/Google seems to be 0755.
+    // TODO(komatsu): nice to make a wrapper function.
+    ::mkdir(dir.c_str(), 0755);
+    dir = FileUtil::JoinPath(dir, "JapaneseInput");
 #else  //  GOOGLE_JAPANESE_INPUT_BUILD
-  dir = FileUtil::JoinPath(dir, "Mozc");
+    dir = FileUtil::JoinPath(dir, "Mozc");
 #endif  //  GOOGLE_JAPANESE_INPUT_BUILD
+  }
 
 #elif defined(OS_ANDROID)
   // For android, we do nothing here because user profile directory,
@@ -237,14 +248,24 @@
   // is injected from Java layer.
 
 #else  // !OS_WIN && !OS_MACOSX && !OS_ANDROID
-  char buf[1024];
-  struct passwd pw, *ppw;
-  const uid_t uid = geteuid();
-  CHECK_EQ(0, getpwuid_r(uid, &pw, buf, sizeof(buf), &ppw))
-      << "Can't get passwd entry for uid " << uid << ".";
-  CHECK_LT(0, strlen(pw.pw_dir))
-      << "Home directory for uid " << uid << " is not set.";
-  dir = FileUtil::JoinPath(pw.pw_dir, ".mozc");
+  configuration_directory_env = ::getenv("MOZC_CONFIGURATION_DIRECTORY");
+  if (configuration_directory_env) {
+    dir = configuration_directory_env;
+  } else {
+    const char *home_env = ::getenv("HOME");
+    if (home_env) {
+      dir = FileUtil::JoinPath(home_env, ".mozc");
+    } else {
+      char buf[1024];
+      struct passwd pw, *ppw;
+      const uid_t uid = geteuid();
+      CHECK_EQ(0, getpwuid_r(uid, &pw, buf, sizeof(buf), &ppw))
+          << "Can't get passwd entry for uid " << uid << ".";
+      CHECK_LT(0, strlen(pw.pw_dir))
+          << "Home directory for uid " << uid << " is not set.";
+      dir = FileUtil::JoinPath(pw.pw_dir, ".mozc");
+    }
+  }
 #endif  // !OS_WIN && !OS_MACOSX && !OS_ANDROID
 
   FileUtil::CreateDirectory(dir);
@@ -356,6 +377,10 @@
 #endif  // OS_WIN
 
 string SystemUtil::GetServerDirectory() {
+  const char *server_directory_env = ::getenv("MOZC_SERVER_DIRECTORY");
+  if (server_directory_env) {
+    return server_directory_env;
+  }
 #ifdef OS_WIN
   DCHECK(SUCCEEDED(Singleton<ProgramFilesX86Cache>::get()->result()));
 #if defined(GOOGLE_JAPANESE_INPUT_BUILD)
@@ -409,6 +434,10 @@
 }
 
 string SystemUtil::GetDocumentDirectory() {
+  const char *documents_directory_env = ::getenv("MOZC_DOCUMENTS_DIRECTORY");
+  if (documents_directory_env) {
+    return documents_directory_env;
+  }
 #if defined(OS_MACOSX)
   return GetServerDirectory();
 #elif defined(MOZC_DOCUMENT_DIRECTORY)
--- /src/handwriting/zinnia_handwriting.cc
+++ /src/handwriting/zinnia_handwriting.cc
@@ -31,6 +31,7 @@
 
 #include "handwriting/zinnia_handwriting.h"
 
+#include <cstdlib>
 #include <memory>
 #include <string>
 
@@ -48,6 +49,10 @@
 
 // static
 string ZinniaHandwriting::GetModelFileName() {
+  const char *zinnia_model_file_env = ::getenv("MOZC_ZINNIA_MODEL_FILE");
+  if (zinnia_model_file_env) {
+    return zinnia_model_file_env;
+  }
 #if defined(MOZC_BUILD)
   return MOZC_ZINNIA_MODEL_FILE;
 #else