Include instructions to extract Mac OS X SDK on Linux using 7zip and SleuthKit

1 files changed, 16 insertions, 1 deletions

diff --git a/doc/README_osx.md b/doc/README_osx.md
index aed3cd97e1..e934b4fc54 100644
--- a/doc/README_osx.md
+++ b/doc/README_osx.md
@@ -36,11 +36,26 @@ Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.1
 ```
 
 Unfortunately, the usual linux tools (7zip, hpmount, loopback mount) are incapable of opening this file.
-To create a tarball suitable for Gitian input, mount the dmg in OS X, then create it with:
+To create a tarball suitable for Gitian input, there are two options:
+
+Using Mac OS X, you can mount the dmg, and then create it with:
 ```
+  $ hdiutil attach Xcode_7.3.1.dmg
   $ tar -C /Volumes/Xcode/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/ -czf MacOSX10.11.sdk.tar.gz MacOSX10.11.sdk
 ```
 
+Alternatively, you can use 7zip and SleuthKit to extract the files one by one.
+The script contrib/macdeploy/extract-osx-sdk.sh automates this. First ensure
+the dmg file is in the current directory, and then run the script. You may wish
+to delete the intermediate 5.hfs file and MacOSX10.11.sdk (the directory) when
+you've confirmed the extraction succeeded.
+
+```bash
+apt-get install p7zip-full sleuthkit
+contrib/macdeploy/extract-osx-sdk.sh
+rm -rf 5.hfs MacOSX10.11.sdk
+```
+
 The Gitian descriptors build 2 sets of files: Linux tools, then Apple binaries
 which are created using these tools. The build process has been designed to
 avoid including the SDK's files in Gitian's outputs. All interim tarballs are