diff --git a/CHANGES b/CHANGES
index 83d68149540..df1f07435db 100644
--- a/CHANGES
+++ b/CHANGES
@@ -2,6 +2,25 @@ Changes prefixed with "(*)" are potentially breaking to scripts or existing
 repositories (changes that are automatically handled by the format upgrade tools
 are not marked).
 
+
+2.0.6:
+* Don't remove git cache objects that may be used [#3831 @AltGr]
+* Don't include .gitattributes in index.tar.gz [#3873 @dra27]
+* Update FAQ uri [#3941 @dra27]
+* Lock: add warning in case of missing locked file [#3939 @rjbou]
+* Directory tracking: fix cached entries retrieving with precise
+  tracking [#4038 @hannesm]
+* Build:
+  * Add sanity checks [#3934 @dra27]
+  * Build man pages using dune [#3902] #dra27]
+  * Add patch and bunzip check for make cold [#4006 @rjbou - fix #3842]
+* Shell:
+  * fish: add colon for fish manpath [#3886 @rjbou - fix #3878]
+* Sandbox:
+    * Add dune cache as rw [#4019 @rjbou - fix #4012]
+    * Do not fail if $HOME/.ccache is missing [#3957 @mseri]
+* opam-devel file: avoid copying extraneous files in opam-devel example [#3999 @maroneze]
+
 2.0.5:
 * Bump src_ext Dune to 1.6.3, allows compilation with OCaml 4.08.0. [#3887 @dra27]
 * Support Dune 1.7.0 and later [#3888 @dra27 - fix #3870]
diff --git a/Makefile b/Makefile
index 5574a489862..71b69e4a8da 100644
--- a/Makefile
+++ b/Makefile
@@ -190,7 +190,7 @@ compiler:
 	env MAKE=$(MAKE) ./shell/bootstrap-ocaml.sh $(OCAML_PORT)
 
 cold: compiler
-	env PATH="`pwd`/bootstrap/ocaml/bin:$$PATH" ./configure $(CONFIGURE_ARGS)
+	env PATH="`pwd`/bootstrap/ocaml/bin:$$PATH" ./configure --enable-cold-check $(CONFIGURE_ARGS)
 	env PATH="`pwd`/bootstrap/ocaml/bin:$$PATH" $(MAKE) lib-ext
 	env PATH="`pwd`/bootstrap/ocaml/bin:$$PATH" $(MAKE)
 
diff --git a/configure b/configure
index 1107e77c464..afe5901002b 100755
--- a/configure
+++ b/configure
@@ -1,6 +1,6 @@
 #! /bin/sh
 # Guess values for system-dependent variables and create Makefiles.
-# Generated by GNU Autoconf 2.69 for opam 2.0.5.
+# Generated by GNU Autoconf 2.69 for opam 2.0.6.
 #
 #
 # Copyright (C) 1992-1996, 1998-2012 Free Software Foundation, Inc.
@@ -578,8 +578,8 @@ MAKEFLAGS=
 # Identity of this package.
 PACKAGE_NAME='opam'
 PACKAGE_TARNAME='opam'
-PACKAGE_VERSION='2.0.5'
-PACKAGE_STRING='opam 2.0.5'
+PACKAGE_VERSION='2.0.6'
+PACKAGE_STRING='opam 2.0.6'
 PACKAGE_BUGREPORT=''
 PACKAGE_URL=''
 
@@ -701,6 +701,7 @@ enable_checks
 enable_developer_mode
 with_mccs
 with_private_runtime
+enable_cold_check
 enable_certificate_check
 '
       ac_precious_vars='build_alias
@@ -1264,7 +1265,7 @@ if test "$ac_init_help" = "long"; then
   # Omit some internal or obsolete options to make the list less imposing.
   # This message is too long to be a string in the A/UX 3.1 sh.
   cat <<_ACEOF
-\`configure' configures opam 2.0.5 to adapt to many kinds of systems.
+\`configure' configures opam 2.0.6 to adapt to many kinds of systems.
 
 Usage: $0 [OPTION]... [VAR=VALUE]...
 
@@ -1326,7 +1327,7 @@ fi
 
 if test -n "$ac_init_help"; then
   case $ac_init_help in
-     short | recursive ) echo "Configuration of opam 2.0.5:";;
+     short | recursive ) echo "Configuration of opam 2.0.6:";;
    esac
   cat <<\_ACEOF
 
@@ -1340,6 +1341,7 @@ Optional Features:
 
   --enable-developer-mode Enable developer features
 
+  --enable-cold-check     Fail on some check necessary for make cold
   --disable-certificate-check
                           Do not check the certificate of opam's dependency
                           archives
@@ -1429,7 +1431,7 @@ fi
 test -n "$ac_init_help" && exit $ac_status
 if $ac_init_version; then
   cat <<\_ACEOF
-opam configure 2.0.5
+opam configure 2.0.6
 generated by GNU Autoconf 2.69
 
 Copyright (C) 2012 Free Software Foundation, Inc.
@@ -1524,7 +1526,7 @@ cat >config.log <<_ACEOF
 This file contains any messages produced by compilers while
 running configure, to aid debugging if configure makes a mistake.
 
-It was created by opam $as_me 2.0.5, which was
+It was created by opam $as_me 2.0.6, which was
 generated by GNU Autoconf 2.69.  Invocation command line was
 
   $ $0 $@
@@ -3169,6 +3171,12 @@ else
 fi
 
 
+# Check whether --enable-cold_check was given.
+if test "${enable_cold_check+set}" = set; then :
+  enableval=$enable_cold_check; COLD_CHECK=yes
+fi
+
+
 if test "x" != "x$LIB_PREFIX"; then :
 
   CPATH=$CPATH:$LIB_PREFIX/include
@@ -4817,6 +4825,15 @@ else
 fi
 
 
+if test "x${COLD_CHECK}" = "xyes" ; then
+  if test "x$PATCH"  = "x" ; then
+    as_fn_error $? "You must have patch installed." "$LINENO" 5
+  fi
+  if test "x$BUNZIP2"  = "x" ; then
+    as_fn_error $? "You must have bunzip2 installed." "$LINENO" 5
+  fi
+fi
+
 if test "${OCAML_OS_TYPE}" = "Win32"; then :
 
   { $as_echo "$as_me:${as_lineno-$LINENO}: checking for a workable solution for ln -s" >&5
@@ -6068,7 +6085,7 @@ cat >>$CONFIG_STATUS <<\_ACEOF || ac_write_fail=1
 # report actual input values of CONFIG_FILES etc. instead of their
 # values after options handling.
 ac_log="
-This file was extended by opam $as_me 2.0.5, which was
+This file was extended by opam $as_me 2.0.6, which was
 generated by GNU Autoconf 2.69.  Invocation command line was
 
   CONFIG_FILES    = $CONFIG_FILES
@@ -6121,7 +6138,7 @@ _ACEOF
 cat >>$CONFIG_STATUS <<_ACEOF || ac_write_fail=1
 ac_cs_config="`$as_echo "$ac_configure_args" | sed 's/^ //; s/[\\""\`\$]/\\\\&/g'`"
 ac_cs_version="\\
-opam config.status 2.0.5
+opam config.status 2.0.6
 configured by $0, generated by GNU Autoconf 2.69,
   with options \\"\$ac_cs_config\\"
 
diff --git a/configure.ac b/configure.ac
index 29762b4f1c8..4b66ebbfaa2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1,5 +1,5 @@
 dnl The line below must be formatted AC_INIT(opam,VERSION) with no extra spaces
-AC_INIT(opam,2.0.5)
+AC_INIT(opam,2.0.6)
 AC_COPYRIGHT(Copyright 2012-2017 OcamlPro SAS)
 
 AC_CONFIG_MACRO_DIR([m4])
@@ -60,6 +60,11 @@ AC_ARG_WITH([private_runtime],
                  [For a mingw-w64 build, manifest the runtime DLLs locally in Opam.Runtime.arch]),,[with_private_runtime=no]
 )
 
+AC_ARG_ENABLE([cold_check],
+  AC_HELP_STRING([--enable-cold-check],
+                 [Fail on some check necessary for make cold]),[COLD_CHECK=yes],[]
+)
+
 AS_IF([test "x" != "x$LIB_PREFIX"], [
   CPATH=$CPATH:$LIB_PREFIX/include
   LIBRARY_PATH=$LIBRARY_PATH:$LIB_PREFIX/lib
@@ -219,6 +224,15 @@ AC_CHECK_TOOL(CPPO,cppo)
 AC_CHECK_TOOL(PATCH,patch)
 AC_CHECK_TOOL(BUNZIP2,bunzip2)
 
+if test "x${COLD_CHECK}" = "xyes" ; then
+  if test "x$PATCH"  = "x" ; then
+    AC_MSG_ERROR([You must have patch installed.])
+  fi
+  if test "x$BUNZIP2"  = "x" ; then
+    AC_MSG_ERROR([You must have bunzip2 installed.])
+  fi
+fi
+
 AS_IF([test "${OCAML_OS_TYPE}" = "Win32"],[
   AC_MSG_CHECKING([for a workable solution for ln -s])
   ln -s configure conftestLink
diff --git a/opam-client.opam b/opam-client.opam
index 4954cbe131d..589930595b7 100644
--- a/opam-client.opam
+++ b/opam-client.opam
@@ -1,5 +1,5 @@
 opam-version: "1.2"
-version: "2.0.5"
+version: "2.0.6"
 maintainer: "opam-devel@lists.ocaml.org"
 authors: [
   "Vincent Bernardoff <vb@luminar.eu.org>"
@@ -21,8 +21,8 @@ build: [
   [make "%{name}%.install"]
 ]
 depends: [
-  "opam-state" {= "2.0.5"}
-  "opam-solver" {= "2.0.5"}
+  "opam-state" {= "2.0.6"}
+  "opam-solver" {= "2.0.6"}
   "re" {>= "1.7.2"}
   "cmdliner" {>= "0.9.8"}
   "dune" {build & >= "1.2.1"}
diff --git a/opam-core.opam b/opam-core.opam
index 8bae34602a0..0692bccba7d 100644
--- a/opam-core.opam
+++ b/opam-core.opam
@@ -1,5 +1,5 @@
 opam-version: "1.2"
-version: "2.0.5"
+version: "2.0.6"
 maintainer: "opam-devel@lists.ocaml.org"
 authors: [
   "Vincent Bernardoff <vb@luminar.eu.org>"
diff --git a/opam-devel.opam b/opam-devel.opam
index d6fdd521bbf..9a33941afbc 100644
--- a/opam-devel.opam
+++ b/opam-devel.opam
@@ -1,5 +1,5 @@
 opam-version: "1.2"
-version: "2.0.5"
+version: "2.0.6"
 maintainer: "opam-devel@lists.ocaml.org"
 authors: [
   "Vincent Bernardoff <vb@luminar.eu.org>"
@@ -22,13 +22,13 @@ build: [
 ]
 build-test: [make "tests"]
 depends: [
-  "opam-client" {= "2.0.5"}
+  "opam-client" {= "2.0.6"}
   "cmdliner" {>= "0.9.8"}
   "dune" {build & >= "1.2.1"}
 ]
 post-messages: [
 "The development version of opam has been successfully compiled into %{lib}%/%{name}%. You should not run it from there, please install the binaries to your PATH, e.g. with
-    sudo cp %{lib}%/%{name}%/* /usr/local/bin
+    sudo cp %{lib}%/%{name}%/opam /usr/local/bin
 
 If you just want to give it a try without altering your current installation, you could use instead:
     alias opam2=\"OPAMROOT=~/.opam2 %{lib}%/%{name}%/opam\""
diff --git a/opam-format.opam b/opam-format.opam
index 78a58cda881..fd81559556d 100644
--- a/opam-format.opam
+++ b/opam-format.opam
@@ -1,5 +1,5 @@
 opam-version: "1.2"
-version: "2.0.5"
+version: "2.0.6"
 maintainer: "opam-devel@lists.ocaml.org"
 authors: [
   "Vincent Bernardoff <vb@luminar.eu.org>"
@@ -21,7 +21,7 @@ build: [
   [make "%{name}%.install"]
 ]
 depends: [
-  "opam-core" {= "2.0.5"}
+  "opam-core" {= "2.0.6"}
   "opam-file-format" {>= "2.0.0~rc2"}
   "dune" {build & >= "1.2.1"}
 ]
diff --git a/opam-installer.opam b/opam-installer.opam
index 80985121471..72ebd300dfc 100644
--- a/opam-installer.opam
+++ b/opam-installer.opam
@@ -1,5 +1,5 @@
 opam-version: "1.2"
-version: "2.0.5"
+version: "2.0.6"
 maintainer: "opam-devel@lists.ocaml.org"
 authors: [
   "Vincent Bernardoff <vb@luminar.eu.org>"
@@ -21,7 +21,7 @@ build: [
   [make "DUNE_ARGS=-p %{name}%" "%{name}%.install"]
 ]
 depends: [
-  "opam-format" {= "2.0.5"}
+  "opam-format" {= "2.0.6"}
   "cmdliner" {>= "0.9.8"}
   "dune" {build & >= "1.2.1"}
 ]
diff --git a/opam-repository.opam b/opam-repository.opam
index 459fb04749e..8c05134870a 100644
--- a/opam-repository.opam
+++ b/opam-repository.opam
@@ -1,5 +1,5 @@
 opam-version: "1.2"
-version: "2.0.5"
+version: "2.0.6"
 maintainer: "opam-devel@lists.ocaml.org"
 authors: [
   "Vincent Bernardoff <vb@luminar.eu.org>"
@@ -21,7 +21,7 @@ build: [
   [make "%{name}%.install"]
 ]
 depends: [
-  "opam-format" {= "2.0.5"}
+  "opam-format" {= "2.0.6"}
   "dune" {build & >= "1.2.1"}
 ]
 available: ocaml-version >= "4.02.3"
diff --git a/opam-solver.opam b/opam-solver.opam
index 7df9e78bb81..3b590c1a3ce 100644
--- a/opam-solver.opam
+++ b/opam-solver.opam
@@ -1,5 +1,5 @@
 opam-version: "1.2"
-version: "2.0.5"
+version: "2.0.6"
 maintainer: "opam-devel@lists.ocaml.org"
 authors: [
   "Vincent Bernardoff <vb@luminar.eu.org>"
@@ -21,7 +21,7 @@ build: [
   [make "%{name}%.install"]
 ]
 depends: [
-  "opam-format" {= "2.0.5"}
+  "opam-format" {= "2.0.6"}
   "mccs" {>= "1.1+9"}
   "dose3" {>= "5"}
   "cudf" {>= "0.7"}
diff --git a/opam-state.opam b/opam-state.opam
index 4a9163a8b71..b1bdc3bbb5f 100644
--- a/opam-state.opam
+++ b/opam-state.opam
@@ -1,5 +1,5 @@
 opam-version: "1.2"
-version: "2.0.5"
+version: "2.0.6"
 maintainer: "opam-devel@lists.ocaml.org"
 authors: [
   "Vincent Bernardoff <vb@luminar.eu.org>"
@@ -21,7 +21,7 @@ build: [
   [make "%{name}%.install"]
 ]
 depends: [
-  "opam-repository" {= "2.0.5"}
+  "opam-repository" {= "2.0.6"}
   "dune" {build & >= "1.2.1"}
 ]
 available: ocaml-version >= "4.02.3"
diff --git a/shell/bundle.sh b/shell/bundle.sh
index 48902fb9676..ff0eb52b819 100755
--- a/shell/bundle.sh
+++ b/shell/bundle.sh
@@ -2,7 +2,7 @@
 set -ue
 
 OCAMLV=4.04.1
-OPAMV=2.0.5
+OPAMV=2.0.6
 OPAM_REPO=https://opam.ocaml.org/2.0
 DEBUG=
 MAKESELF=
diff --git a/src/client/opamCommands.ml b/src/client/opamCommands.ml
index bce436804bf..a3e3c88693b 100644
--- a/src/client/opamCommands.ml
+++ b/src/client/opamCommands.ml
@@ -3022,7 +3022,14 @@ let clean =
     if download_cache then
       (OpamConsole.msg "Clearing cache of downloaded files\n";
        rmdir (OpamPath.archives_dir root);
-       cleandir (OpamRepositoryPath.download_cache root));
+       List.iter (fun dir ->
+           match OpamFilename.(Base.to_string (basename_dir dir)) with
+           | "git" ->
+             (try OpamFilename.exec dir ~name:"git gc" [["git"; "gc"]]
+              with e -> OpamStd.Exn.fatal e)
+           | _ -> cleandir dir
+         )
+         (OpamFilename.dirs (OpamRepositoryPath.download_cache root)));
     if logs then
       (OpamConsole.msg "Clearing logs\n";
        cleandir (OpamPath.log root))
diff --git a/src/client/opamConfigCommand.ml b/src/client/opamConfigCommand.ml
index 4cb579c7b94..919011e64cc 100644
--- a/src/client/opamConfigCommand.ml
+++ b/src/client/opamConfigCommand.ml
@@ -166,7 +166,12 @@ let print_sexp_env env =
 
 let rec print_fish_env env =
   let set_arr_cmd k v =
-    let v = OpamStd.String.split v ':' in
+    let v =
+      OpamStd.String.split v ':'
+      |> function
+      | x::v' -> (":"^x)::v'
+      | v -> v
+    in
     OpamConsole.msg "set -gx %s %s;\n" k
       (OpamStd.List.concat_map " "
          (fun v ->
diff --git a/src/core/opamDirTrack.ml b/src/core/opamDirTrack.ml
index 45ed3a0ac88..00428ca2a43 100644
--- a/src/core/opamDirTrack.ml
+++ b/src/core/opamDirTrack.ml
@@ -60,7 +60,7 @@ let cached_digest =
   fun f size mtime ->
     try
       let csize, cmtime, digest = Hashtbl.find item_cache f in
-      if csize = size || mtime = cmtime then Digest.to_hex digest
+      if csize = size && mtime = cmtime then Digest.to_hex digest
       else raise Not_found
     with Not_found ->
       let digest = Digest.file f in
diff --git a/src/repository/opamHTTP.ml b/src/repository/opamHTTP.ml
index 2807fc60b09..4d1fd91448e 100644
--- a/src/repository/opamHTTP.ml
+++ b/src/repository/opamHTTP.ml
@@ -100,5 +100,5 @@ let make_index_tar_gz repo_root =
     let to_include = [ "version"; "packages"; "repo" ] in
     match List.filter Sys.file_exists to_include with
     | [] -> ()
-    | d  -> OpamSystem.command ("tar" :: "czhf" :: "index.tar.gz" :: d)
+    | d  -> OpamSystem.command ("tar" :: "czhf" :: "index.tar.gz" :: "--exclude=.git*" :: d)
   )
diff --git a/src/state/shellscripts/bwrap.sh b/src/state/shellscripts/bwrap.sh
index ef0c52e84dd..1021d2eb909 100755
--- a/src/state/shellscripts/bwrap.sh
+++ b/src/state/shellscripts/bwrap.sh
@@ -73,6 +73,12 @@ add_ccache_mount() {
   fi
 }
 
+add_dune_cache_mount() {
+  DUNE_CACHE=${XDG_CACHE_HOME:-$HOME/.cache}/dune
+  mkdir -p ${DUNE_CACHE}
+  add_mounts rw $DUNE_CACHE
+ }
+
 # This case-switch should remain identical between the different sandbox implems
 COMMAND="$1"; shift
 case "$COMMAND" in
@@ -84,6 +90,7 @@ case "$COMMAND" in
         add_mounts ro "$OPAM_SWITCH_PREFIX"
         add_mounts rw "$PWD"
         add_ccache_mount
+        add_dune_cache_mount
         ;;
     install)
         # mount unusual path in ro
diff --git a/src/state/shellscripts/sandbox_exec.sh b/src/state/shellscripts/sandbox_exec.sh
index 4926239a4fd..6019d78f562 100644
--- a/src/state/shellscripts/sandbox_exec.sh
+++ b/src/state/shellscripts/sandbox_exec.sh
@@ -6,11 +6,13 @@ POL="$POL"'(allow network* (remote unix))'
 POL="$POL"'(allow file-write* (literal "/dev/null") (literal "/dev/dtracehelper"))'
 
 add_mounts() {
-    local DIR="$(cd "$2" && pwd -P)"
-    case "$1" in
-        ro) POL="$POL"'(deny file-write* (subpath "'"$DIR"'"))';;
-        rw) POL="$POL"'(allow file-write* (subpath "'"$DIR"'"))';;
-    esac
+    if [ -d "$2" ]; then
+      local DIR="$(cd "$2" && pwd -P)"
+      case "$1" in
+          ro) POL="$POL"'(deny file-write* (subpath "'"$DIR"'"))';;
+          rw) POL="$POL"'(allow file-write* (subpath "'"$DIR"'"))';;
+      esac
+    fi
 }
 
 if [ -z ${TMPDIR+x} ]; then
@@ -44,6 +46,12 @@ add_ccache_mount() {
   fi
 }
 
+add_dune_cache_mount() {
+  DUNE_CACHE=${XDG_CACHE_HOME:-$HOME/.cache}/dune
+  mkdir -p ${DUNE_CACHE}
+  add_mounts rw $DUNE_CACHE
+ }
+
 # This case-switch should remain identical between the different sandbox implems
 COMMAND="$1"; shift
 case "$COMMAND" in
@@ -51,6 +59,7 @@ case "$COMMAND" in
         add_mounts ro "$OPAM_SWITCH_PREFIX"
         add_mounts rw "$PWD"
         add_ccache_mount
+        add_dune_cache_mount
         ;;
     install)
         add_mounts rw "$OPAM_SWITCH_PREFIX"