diff --git a/install.c b/install.c
index 707cda4..9d7595e 100644
--- a/install.c
+++ b/install.c
@@ -36,11 +36,9 @@
 #define ASSUMED_UPDATE_BINARY_NAME  "META-INF/com/google/android/update-binary"
 #define PUBLIC_KEYS_FILE "/res/keys"
 
-static const char *LAST_INSTALL_FILE = "/cache/recovery/last_install";
-
 // If the package contains an update binary, extract it and run it.
 static int
-try_update_binary(const char *path, ZipArchive *zip) {
+try_update_binary(const char *path, ZipArchive *zip, int* wipe_cache) {
     const ZipEntry* binary_entry =
             mzFindZipEntry(zip, ASSUMED_UPDATE_BINARY_NAME);
     if (binary_entry == NULL) {
@@ -54,7 +52,7 @@
     if (fd < 0) {
         mzCloseZipArchive(zip);
         LOGE("Can't make %s\n", binary);
-        return 1;
+        return INSTALL_ERROR;
     }
     bool ok = mzExtractZipEntryToFile(zip, binary_entry, fd);
     close(fd);
@@ -62,7 +60,7 @@
 
     if (!ok) {
         LOGE("Can't copy %s\n", ASSUMED_UPDATE_BINARY_NAME);
-        return 1;
+        return INSTALL_ERROR;
     }
 
     int pipefd[2];
@@ -119,6 +117,8 @@
     }
     close(pipefd[1]);
 
+    *wipe_cache = 0;
+
     char buffer[1024];
     FILE* from_child = fdopen(pipefd[0], "r");
     while (fgets(buffer, sizeof(buffer), from_child) != NULL) {
@@ -145,6 +145,8 @@
             } else {
                 ui_print("\n");
             }
+        } else if (strcmp(command, "wipe_cache") == 0) {
+            *wipe_cache = 1;
         } else {
             LOGE("unknown command [%s]\n", command);
         }
@@ -236,7 +238,7 @@
 }
 
 static int
-really_install_package(const char *path)
+really_install_package(const char *path, int* wipe_cache)
 {
     ui_set_background(BACKGROUND_ICON_INSTALLING);
     ui_print("Finding update package...\n");
@@ -285,25 +287,24 @@
     /* Verify and install the contents of the package.
      */
     ui_print("Installing update...\n");
-    return try_update_binary(path, &zip);
+    return try_update_binary(path, &zip, wipe_cache);
 }
 
 int
-install_package(const char* path)
+install_package(const char* path, int* wipe_cache, const char* install_file)
 {
-    FILE* install_log = fopen_path(LAST_INSTALL_FILE, "w");
+    FILE* install_log = fopen_path(install_file, "w");
     if (install_log) {
         fputs(path, install_log);
         fputc('\n', install_log);
     } else {
         LOGE("failed to open last_install: %s\n", strerror(errno));
     }
-    int result = really_install_package(path);
+    int result = really_install_package(path, wipe_cache);
     if (install_log) {
         fputc(result == INSTALL_SUCCESS ? '1' : '0', install_log);
         fputc('\n', install_log);
         fclose(install_log);
-        chmod(LAST_INSTALL_FILE, 0644);
     }
     return result;
 }
diff --git a/install.h b/install.h
index a7ebc09..5ebe160 100644
--- a/install.h
+++ b/install.h
@@ -20,6 +20,10 @@
 #include "common.h"
 
 enum { INSTALL_SUCCESS, INSTALL_ERROR, INSTALL_CORRUPT };
-int install_package(const char *root_path);
+// Install the package specified by root_path.  If INSTALL_SUCCESS is
+// returned and *wipe_cache is true on exit, caller should wipe the
+// cache partition.
+int install_package(const char *root_path, int* wipe_cache,
+                    const char* install_file);
 
 #endif  // RECOVERY_INSTALL_H_
diff --git a/recovery.c b/recovery.c
index 1e3eb5a..06d6498 100644
--- a/recovery.c
+++ b/recovery.c
@@ -52,9 +52,11 @@
 static const char *INTENT_FILE = "/cache/recovery/intent";
 static const char *LOG_FILE = "/cache/recovery/log";
 static const char *LAST_LOG_FILE = "/cache/recovery/last_log";
+static const char *LAST_INSTALL_FILE = "/cache/recovery/last_install";
 static const char *CACHE_ROOT = "/cache";
 static const char *SDCARD_ROOT = "/sdcard";
 static const char *TEMPORARY_LOG_FILE = "/tmp/recovery.log";
+static const char *TEMPORARY_INSTALL_FILE = "/tmp/last_install";
 static const char *SIDELOAD_TEMP_DIR = "/tmp/sideload";
 
 extern UIParameters ui_parameters;    // from ui.c
@@ -223,15 +225,13 @@
 static long tmplog_offset = 0;
 
 static void
-copy_log_file(const char* destination, int append) {
+copy_log_file(const char* source, const char* destination, int append) {
     FILE *log = fopen_path(destination, append ? "a" : "w");
     if (log == NULL) {
         LOGE("Can't open %s\n", destination);
     } else {
-        FILE *tmplog = fopen(TEMPORARY_LOG_FILE, "r");
-        if (tmplog == NULL) {
-            LOGE("Can't open %s\n", TEMPORARY_LOG_FILE);
-        } else {
+        FILE *tmplog = fopen(source, "r");
+        if (tmplog != NULL) {
             if (append) {
                 fseek(tmplog, tmplog_offset, SEEK_SET);  // Since last write
             }
@@ -240,7 +240,7 @@
             if (append) {
                 tmplog_offset = ftell(tmplog);
             }
-            check_and_fclose(tmplog, TEMPORARY_LOG_FILE);
+            check_and_fclose(tmplog, source);
         }
         check_and_fclose(log, destination);
     }
@@ -265,9 +265,13 @@
     }
 
     // Copy logs to cache so the system can find out what happened.
-    copy_log_file(LOG_FILE, true);
-    copy_log_file(LAST_LOG_FILE, false);
+    copy_log_file(TEMPORARY_LOG_FILE, LOG_FILE, true);
+    copy_log_file(TEMPORARY_LOG_FILE, LAST_LOG_FILE, false);
+    copy_log_file(TEMPORARY_INSTALL_FILE, LAST_INSTALL_FILE, false);
+    chmod(LOG_FILE, 0600);
+    chown(LOG_FILE, 1000, 1000);   // system user
     chmod(LAST_LOG_FILE, 0640);
+    chmod(LAST_INSTALL_FILE, 0644);
 
     // Reset to mormal system boot so recovery won't cycle indefinitely.
     struct bootloader_message boot;
@@ -280,6 +284,7 @@
         LOGW("Can't unlink %s\n", COMMAND_FILE);
     }
 
+    ensure_path_unmounted(CACHE_ROOT);
     sync();  // For good measure.
 }
 
@@ -289,6 +294,8 @@
     ui_show_indeterminate_progress();
     ui_print("Formatting %s...\n", volume);
 
+    ensure_path_unmounted(volume);
+
     if (strcmp(volume, "/cache") == 0) {
         // Any part of the log we'd copied to cache is now gone.
         // Reset the pointer so we copy from the beginning of the temp
@@ -469,7 +476,8 @@
 }
 
 static int
-update_directory(const char* path, const char* unmount_when_done) {
+update_directory(const char* path, const char* unmount_when_done,
+                 int* wipe_cache) {
     ensure_path_mounted(path);
 
     const char* MENU_HEADERS[] = { "Choose a package to install:",
@@ -558,7 +566,7 @@
             strlcat(new_path, "/", PATH_MAX);
             strlcat(new_path, item, PATH_MAX);
             new_path[strlen(new_path)-1] = '\0';  // truncate the trailing '/'
-            result = update_directory(new_path, unmount_when_done);
+            result = update_directory(new_path, unmount_when_done, wipe_cache);
             if (result >= 0) break;
         } else {
             // selected a zip file:  attempt to install it, and return
@@ -575,7 +583,7 @@
                 ensure_path_unmounted(unmount_when_done);
             }
             if (copy) {
-                result = install_package(copy);
+                result = install_package(copy, wipe_cache, TEMPORARY_INSTALL_FILE);
                 free(copy);
             } else {
                 result = INSTALL_ERROR;
@@ -650,6 +658,7 @@
         chosen_item = device_perform_action(chosen_item);
 
         int status;
+        int wipe_cache;
         switch (chosen_item) {
             case ITEM_REBOOT:
                 return;
@@ -667,7 +676,15 @@
                 break;
 
             case ITEM_APPLY_SDCARD:
-                status = update_directory(SDCARD_ROOT, SDCARD_ROOT);
+                status = update_directory(SDCARD_ROOT, SDCARD_ROOT, &wipe_cache);
+                if (status == INSTALL_SUCCESS && wipe_cache) {
+                    ui_print("\n-- Wiping cache (at package request)...\n");
+                    if (erase_volume("/cache")) {
+                        ui_print("Cache wipe failed.\n");
+                    } else {
+                        ui_print("Cache wipe complete.\n");
+                    }
+                }
                 if (status >= 0) {
                     if (status != INSTALL_SUCCESS) {
                         ui_set_background(BACKGROUND_ICON_ERROR);
@@ -681,7 +698,15 @@
                 break;
             case ITEM_APPLY_CACHE:
                 // Don't unmount cache at the end of this.
-                status = update_directory(CACHE_ROOT, NULL);
+                status = update_directory(CACHE_ROOT, NULL, &wipe_cache);
+                if (status == INSTALL_SUCCESS && wipe_cache) {
+                    ui_print("\n-- Wiping cache (at package request)...\n");
+                    if (erase_volume("/cache")) {
+                        ui_print("Cache wipe failed.\n");
+                    } else {
+                        ui_print("Cache wipe complete.\n");
+                    }
+                }
                 if (status >= 0) {
                     if (status != INSTALL_SUCCESS) {
                         ui_set_background(BACKGROUND_ICON_ERROR);
@@ -768,7 +793,12 @@
     int status = INSTALL_SUCCESS;
 
     if (update_package != NULL) {
-        status = install_package(update_package);
+        status = install_package(update_package, &wipe_cache, TEMPORARY_INSTALL_FILE);
+        if (status == INSTALL_SUCCESS && wipe_cache) {
+            if (erase_volume("/cache")) {
+                LOGE("Cache wipe (requested by package) failed.");
+            }
+        }
         if (status != INSTALL_SUCCESS) ui_print("Installation aborted.\n");
     } else if (wipe_data) {
         if (device_wipe_data()) status = INSTALL_ERROR;
diff --git a/updater/install.c b/updater/install.c
index 0396bae..7b4b99b 100644
--- a/updater/install.c
+++ b/updater/install.c
@@ -1024,6 +1024,14 @@
     return StringValue(buffer);
 }
 
+Value* WipeCacheFn(const char* name, State* state, int argc, Expr* argv[]) {
+    if (argc != 0) {
+        return ErrorAbort(state, "%s() expects no args, got %d", name, argc);
+    }
+    fprintf(((UpdaterInfo*)(state->cookie))->cmd_pipe, "wipe_cache\n");
+    return StringValue(strdup("t"));
+}
+
 Value* RunProgramFn(const char* name, State* state, int argc, Expr* argv[]) {
     if (argc < 1) {
         return ErrorAbort(state, "%s() expects at least 1 arg", name);
@@ -1198,6 +1206,8 @@
     RegisterFunction("read_file", ReadFileFn);
     RegisterFunction("sha1_check", Sha1CheckFn);
 
+    RegisterFunction("wipe_cache", WipeCacheFn);
+
     RegisterFunction("ui_print", UIPrintFn);
 
     RegisterFunction("run_program", RunProgramFn);