diff --git a/cspell.json b/cspell.json
index d4bbb9d..e52f6db 100644
--- a/cspell.json
+++ b/cspell.json
@@ -152,6 +152,7 @@
     "certstore",
     "CFPREFERENCES",
     "cfprefsd",
+    "cgroupv",
     "chaput",
     "chardev",
     "chatops",
@@ -333,6 +334,7 @@
     "dscacheutil",
     "dscresource",
     "dslocal",
+    "ducktype",
     "DUPEUX",
     "DWORDLONG",
     "DYNALINK",
@@ -358,6 +360,7 @@
     "encap",
     "Encryptor",
     "encryptor",
+    "endgrent",
     "endlocal",
     "entriesread",
     "envdata",
@@ -451,6 +454,7 @@
     "GETFD",
     "GETFL",
     "getgr",
+    "getgrent",
     "getgrgid",
     "getgrnam",
     "gethostbyname",
@@ -704,6 +708,7 @@
     "loginclass",
     "loginwindow",
     "LOGLOCATION",
+    "LOGNAME",
     "logopts",
     "logstring",
     "LONGLONG",
@@ -1017,6 +1022,7 @@
     "PFILETIME",
     "PFLOAT",
     "PGENERICMAPPING",
+    "pgid",
     "phabricator",
     "PHALF",
     "PHANDLE",
@@ -1245,6 +1251,8 @@
     "Scriptable",
     "SCROLLBAR",
     "SCROLLBARS",
+    "secondarygroups",
+    "seconderies",
     "secontext",
     "secoption",
     "secopts",
@@ -1291,6 +1299,7 @@
     "SETTINGCHANGE",
     "setuid",
     "SETX",
+    "sgids",
     "SHARENAME",
     "SHAs",
     "shas",
@@ -1626,6 +1635,7 @@
     "WINVER",
     "WKSTA",
     "WMIGUID",
+    "WNOHANG",
     "woot",
     "workdir",
     "WPARAM",
diff --git a/lib/mixlib/shellout/unix.rb b/lib/mixlib/shellout/unix.rb
index a2b918b..a2fc4a2 100644
--- a/lib/mixlib/shellout/unix.rb
+++ b/lib/mixlib/shellout/unix.rb
@@ -112,7 +112,7 @@ def run_command
           unless ready_buffers
             @execution_time += READ_WAIT_TIME
             if @execution_time >= timeout && !@result
-              # kill the bad proccess
+              # kill the bad process
               reap_errant_child
               # read anything it wrote when we killed it
               attempt_buffer_read
@@ -288,30 +288,50 @@ def attempt_buffer_read(timeout = READ_WAIT_TIME)
         ready
       end
 
-      def read_stdout_to_buffer
-        while ( chunk = child_stdout.read_nonblock(READ_SIZE) )
-          @stdout << chunk
-          @live_stdout << chunk if @live_stdout
+      # Drain everything currently readable on +io+ into +buffer+, and into
+      # +live+ as well when a live stream is attached.
+      #
+      # Without a live stream we can hand read_nonblock a scratch buffer to
+      # read into and reuse it for every read, rather than letting it allocate
+      # a fresh READ_SIZE String each time -- for an output-heavy command that
+      # is nearly all of the garbage this class produces. Reuse is safe here
+      # only because #<< copies the bytes into +buffer+.
+      #
+      # A live stream is free to hold onto whatever it is handed, so when one
+      # is attached each read gets its own String, exactly as before.
+      def drain(io, buffer, live, scratch)
+        if live
+          while ( chunk = io.read_nonblock(READ_SIZE) )
+            buffer << chunk
+            live << chunk
+          end
+        else
+          while ( chunk = io.read_nonblock(READ_SIZE, scratch) )
+            buffer << chunk
+          end
         end
+      end
+
+      def read_buffer(name)
+        (@read_buffers ||= {})[name] ||= String.new
+      end
+
+      def read_stdout_to_buffer
+        drain(child_stdout, @stdout, @live_stdout, read_buffer(:stdout))
       rescue Errno::EAGAIN
       rescue EOFError
         open_pipes.delete(child_stdout)
       end
 
       def read_stderr_to_buffer
-        while ( chunk = child_stderr.read_nonblock(READ_SIZE) )
-          @stderr << chunk
-          @live_stderr << chunk if @live_stderr
-        end
+        drain(child_stderr, @stderr, @live_stderr, read_buffer(:stderr))
       rescue Errno::EAGAIN
       rescue EOFError
         open_pipes.delete(child_stderr)
       end
 
       def read_process_status_to_buffer
-        while ( chunk = child_process_status.read_nonblock(READ_SIZE) )
-          @process_status << chunk
-        end
+        drain(child_process_status, @process_status, nil, read_buffer(:process_status))
       rescue Errno::EAGAIN
       rescue EOFError
         open_pipes.delete(child_process_status)