diff --git a/.travis.yml b/.travis.yml
index 8df57383f..fac1d94fd 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -71,7 +71,7 @@ script:
   - make all
   - travis_retry make testfront
   - luajit $(which luacheck) --no-color -q frontend | tee ./luacheck.out
-  - test $(grep Total ./luacheck.out | awk '{print $2}') -le 168
+  - test $(grep Total ./luacheck.out | awk '{print $2}') -le 140
 
 after_success:
   - make coverage
diff --git a/frontend/apps/filemanager/filemanager.lua b/frontend/apps/filemanager/filemanager.lua
index 40b230eb5..fb3edb32c 100644
--- a/frontend/apps/filemanager/filemanager.lua
+++ b/frontend/apps/filemanager/filemanager.lua
@@ -22,7 +22,8 @@ local Font = require("ui/font")
 local DEBUG = require("dbg")
 local _ = require("gettext")
 
-function getDefaultDir()
+
+local function getDefaultDir()
     if Device:isKindle() then
         return "/mnt/us/documents"
     elseif Device:isKobo() then
@@ -34,7 +35,7 @@ function getDefaultDir()
     end
 end
 
-function restoreScreenMode()
+local function restoreScreenMode()
     local screen_mode = G_reader_settings:readSetting("fm_screen_mode")
     if Screen:getScreenMode() ~= screen_mode then
         Screen:setScreenMode(screen_mode or "portrait")
@@ -273,7 +274,7 @@ function FileManager:deleteFile(file)
 
     local is_doc = DocumentRegistry:getProvider(file_abs_path)
     ok, err = os.remove(file_abs_path)
-    if err == nil then
+    if ok and err == nil then
         if is_doc ~= nil then
             -- also delete history/settings for documents
             local sidecar_dir = docsettings:getSidecarDir(file_abs_path)
@@ -281,7 +282,8 @@ function FileManager:deleteFile(file)
                 util.purgeDir(sidecar_dir)
             end
             local legacy_history_file = docsettings:getHistoryPath(file)
-            ok, err = os.remove(legacy_history_file)
+            -- @todo: check return from os.remove
+            os.remove(legacy_history_file)
         end
         UIManager:show(InfoMessage:new{
             text = util.template(_("Successfully deleted %1"), file),
diff --git a/frontend/apps/filemanager/filemanagermenu.lua b/frontend/apps/filemanager/filemanagermenu.lua
index fb48be2f2..593af668b 100644
--- a/frontend/apps/filemanager/filemanagermenu.lua
+++ b/frontend/apps/filemanager/filemanagermenu.lua
@@ -85,7 +85,6 @@ function FileManagerMenu:setUpdateItemTable()
         checked_func = function() return self.ui.file_chooser.show_hidden end,
         callback = function() self.ui:toggleHiddenFiles() end
     })
-    local FileManager = require("apps/filemanager/filemanager")
     table.insert(self.tab_item_table.setting, self.ui:getSortingMenuTable())
     table.insert(self.tab_item_table.setting, {
         text = _("Reverse sorting"),
@@ -125,10 +124,10 @@ function FileManagerMenu:setUpdateItemTable()
     table.insert(self.tab_item_table.tools, {
         text = _("OPDS catalog"),
         callback = function()
+            local FileManager = require("apps/filemanager/filemanager")
             local OPDSCatalog = require("apps/opdscatalog/opdscatalog")
             function OPDSCatalog:onExit()
-                DEBUG("refresh filemanager")
-                filemanager:onRefresh()
+                FileManager:onRefresh()
             end
             OPDSCatalog:showCatalog()
         end,
diff --git a/frontend/ui/message/filemessagequeue.lua b/frontend/ui/message/filemessagequeue.lua
index a7ae45ee1..8125c0ae2 100644
--- a/frontend/ui/message/filemessagequeue.lua
+++ b/frontend/ui/message/filemessagequeue.lua
@@ -1,7 +1,7 @@
 local ffi = require("ffi")
 local DEBUG = require("dbg")
 local MessageQueue = require("ui/message/messagequeue")
-local dummy = require("ffi/zeromq_h")
+local _ = require("ffi/zeromq_h")
 local czmq = ffi.load("libs/libczmq.so.1")
 local filemq = ffi.load("libs/libfmq.so.1")
 
diff --git a/frontend/ui/message/messagequeue.lua b/frontend/ui/message/messagequeue.lua
index 0d3a06065..8241b1c78 100644
--- a/frontend/ui/message/messagequeue.lua
+++ b/frontend/ui/message/messagequeue.lua
@@ -1,11 +1,9 @@
 local ffi = require("ffi")
-local util = require("ffi/util")
 local Event = require("ui/event")
 local DEBUG = require("dbg")
 
-local dummy = require("ffi/zeromq_h")
+local _ = require("ffi/zeromq_h")
 local czmq = ffi.load("libs/libczmq.so.1")
-local zyre = ffi.load("libs/libzyre.so.1")
 
 local MessageQueue = {}
 
@@ -39,7 +37,6 @@ function MessageQueue:handleZMsgs(messages)
     end
     local function pop_string()
         local str_p = czmq.zmsg_popstr(messages[1])
-        local message_size = czmq.zmsg_size(messages[1])
         local res = ffi.string(str_p)
         czmq.zstr_free(ffi.new('char *[1]', str_p))
         drop_message()
@@ -64,7 +61,6 @@ function MessageQueue:handleZMsgs(messages)
         return header
     end
     if #messages == 0 then return end
-    local message_size = czmq.zmsg_size(messages[1])
     local command = pop_string()
     DEBUG("ØMQ message", command)
     if command == "ENTER" then
diff --git a/frontend/ui/message/streammessagequeue.lua b/frontend/ui/message/streammessagequeue.lua
index f6c0dad09..9978f2b76 100644
--- a/frontend/ui/message/streammessagequeue.lua
+++ b/frontend/ui/message/streammessagequeue.lua
@@ -1,6 +1,5 @@
 local ffi = require("ffi")
 local DEBUG = require("dbg")
-local Event = require("ui/event")
 local MessageQueue = require("ui/message/messagequeue")
 
 local _ = require("ffi/zeromq_h")
@@ -24,7 +23,8 @@ function StreamMessageQueue:start()
     end
     local id_size = ffi.new("size_t[1]", 256)
     local buffer = ffi.new("uint8_t[?]", id_size[0])
-    rc = zmq.zmq_getsockopt(self.socket, ffi.C.ZMQ_IDENTITY, buffer, id_size)
+    -- @todo: check return of zmq_getsockopt
+    zmq.zmq_getsockopt(self.socket, ffi.C.ZMQ_IDENTITY, buffer, id_size)
     self.id = ffi.string(buffer, id_size[0])
     DEBUG("id", #self.id, self.id)
 end
@@ -65,7 +65,7 @@ function StreamMessageQueue:waitEvent()
     while czmq.zpoller_wait(self.poller, 0) ~= nil and wait_packages > 0 do
         local id_frame = czmq.zframe_recv(self.socket)
         if id_frame ~= nil then
-            local id = self:handleZframe(id_frame)
+            self:handleZframe(id_frame)
         end
         local frame = czmq.zframe_recv(self.socket)
         if frame ~= nil then
diff --git a/frontend/ui/message/zyremessagequeue.lua b/frontend/ui/message/zyremessagequeue.lua
index 3f2d988b5..d1806353c 100644
--- a/frontend/ui/message/zyremessagequeue.lua
+++ b/frontend/ui/message/zyremessagequeue.lua
@@ -1,10 +1,8 @@
 local ffi = require("ffi")
 local DEBUG = require("dbg")
-local util = require("ffi/util")
-local Event = require("ui/event")
 local MessageQueue = require("ui/message/messagequeue")
 
-local dummy = require("ffi/zeromq_h")
+local _ = require("ffi/zeromq_h")
 local czmq = ffi.load("libs/libczmq.so.1")
 local zyre = ffi.load("libs/libzyre.so.1")
 
diff --git a/frontend/ui/widget/filechooser.lua b/frontend/ui/widget/filechooser.lua
index 12b740581..ad0adb540 100644
--- a/frontend/ui/widget/filechooser.lua
+++ b/frontend/ui/widget/filechooser.lua
@@ -99,9 +99,9 @@ function FileChooser:genItemTableFromPath(path)
 
     local item_table = {}
     for i, dir in ipairs(dirs) do
-        local path = self.path.."/"..dir.name
+        local subdir_path = self.path.."/"..dir.name
         local items = 0
-        local ok, iter, dir_obj = pcall(lfs.dir, path)
+        ok, iter, dir_obj = pcall(lfs.dir, subdir_path)
         if ok then
             for f in iter, dir_obj do
                 items = items + 1
@@ -116,13 +116,13 @@ function FileChooser:genItemTableFromPath(path)
         table.insert(item_table, {
             text = dir.name.."/",
             mandatory = istr,
-            path = path
+            path = subdir_path
         })
     end
     for _, file in ipairs(files) do
         local full_path = self.path.."/"..file.name
         local file_size = lfs.attributes(full_path, "size") or 0
-        local sstr = ""
+        local sstr
         if file_size > 1024*1024 then
             sstr = string.format("%4.1f MB", file_size/1024/1024)
         elseif file_size > 1024 then
diff --git a/frontend/ui/widget/touchmenu.lua b/frontend/ui/widget/touchmenu.lua
index 85dec16fa..d50b6cacf 100644
--- a/frontend/ui/widget/touchmenu.lua
+++ b/frontend/ui/widget/touchmenu.lua
@@ -149,13 +149,13 @@ function TouchMenuBar:init()
     local icon_sep_width = Screen:scaleBySize(2)
     local icons_sep_width = icon_sep_width * (#self.icons + 1)
     -- we assume all icons are of the same width
-    local ib = IconButton:new{icon_file = self.icons[1]}
-    local content_width = ib:getSize().w * #self.icons + icons_sep_width
+    local tmp_ib = IconButton:new{icon_file = self.icons[1]}
+    local content_width = tmp_ib:getSize().w * #self.icons + icons_sep_width
     local spacing_width = (self.width - content_width)/(#self.icons*2)
     local spacing = HorizontalSpan:new{
         width = math.min(spacing_width, Screen:scaleBySize(20))
     }
-    self.height = ib:getSize().h + Screen:scaleBySize(10)
+    self.height = tmp_ib:getSize().h + Screen:scaleBySize(10)
     self.show_parent = self.show_parent or self
     self.bar_icon_group = HorizontalGroup:new{}
     -- build up image widget for menu icon bar
@@ -225,7 +225,6 @@ function TouchMenuBar:init()
         table.insert(self.bar_icon_group, self.icon_widgets[k])
         table.insert(self.bar_icon_group, icon_sep)
 
-        start_seg = _start_seg
         end_seg = _end_seg
     end
 
@@ -451,7 +450,7 @@ function TouchMenu:updateItems()
                 --VerticalSpan:new{
                     --width = self.item_height
                 --})
-            --break
+            break
         end -- if i <= self.items
     end -- for c=1, self.perpage