Brew afsctool on your own for Mac OS Sierra

Recently, I came across an error message while compressing the document with HFS+ compression using open source tool afsctool. The repository on Homebrew project is still on version 1.6.4.

Message comes up every time: "Unable to compress file."

Someone on Github has figured out what's happening and has a solution. The Github user has pointed out that the filesystem on Sierra returns a different value of file type than its predecessor. This renders afsctool useless and return error message at all time. But the suggested change has never been updated on the original source repository of afsctool.

With a little patience for not using this tool, I made up my mind. I think it's time to homebrew our software tool before the Author patches the source code for this.

Here's the recipe:

Before your own compiling work, you might want to uninstall the outdated brew formula for afsctool:

$
$ brew uninstall afsctool

Make sure gcc is installed properly on your Mac.

Take a look at the Hombrew formulas for afsctool via http://brewformulas.org/Afsctool

Take a look at the source file from there: https://github.com/Homebrew/homebrew-core/tree/master/Formula/afsctool.rb

We found a URL from there: https://docs.google.com/uc?export=download&id=0BwQlnXqL939ZQjBQNEhRQUo0aUk

Also, take a look at the parameters called from the def() function call. Highlighted parameters will be useful for compiling:

def install
    cd "afsctool_34" do
      system ENV.cc, ENV.cflags, "-lz",
         "-framework", "CoreServices", "-o", "afsctool", "afsctool.c"
      bin.install "afsctool"
    end
end

Grab the source code ZIP of afsctool from the above URL.

Extract the ZIP file to a temporary location.

Find afsctool.c and amend the file according to this Github post.

Try compiling the .c file afsctool.c with GCC compiler using the aforementioned parameters from brew formula:

$
$ gcc -lz -framework CoreServices -o afsctool afsctool.c

Copy the compile file afsctool to the common bin folder for easy access:

$
$ cp ./afsctool /usr/local/bin/afsctool

Well, it's time to have a try on our new compiled tool:

$ afsctool -cv ./afsctool.c
/afsctool_34/afsctool.c:
File content type: public.c-source
File size (uncompressed data fork; reported size by Mac OS 10.6+ Finder): 79339 bytes / 79 KB (kilobytes) / 77 KiB (kibibytes)
File size (compressed data fork - decmpfs xattr; reported size by Mac OS 10.0-10.5 Finder): 13396 bytes / 16 KB (kilobytes) / 16 KiB (kibibytes)
File size (compressed data fork): 13412 bytes / 16 KB (kilobytes) / 16 KiB (kibibytes)
Compression savings: 83.1%
Number of extended attributes: 4
Total size of extended attribute data: 50 bytes
Approximate overhead of extended attributes: 1608 bytes
Approximate total file size (compressed data fork + EA + EA overhead + file overhead): 18306 bytes / 18 KB (kilobytes) / 18 KiB (kibibytes)

Finally, the compression works again.

By the way, we may need to keep watching until one day an updated brew formula is available to tackle this problem for Sierra.

Quickfix: Boot up screen stuck with spin freezes after Mac OS Sierra upgrade

After a major upgrade of Mac OS Sierra, my MacBook didn't boot up anymore. It freezes on the grey screen with dead spinning wheel.

After checking any non-apple Kext module in Safe mode and fixing any disk error in DiskUtility in Recovery mode, I nearly have no clue on what's happening to the hard drive.

Here come across 7 steps which can be useful for anyone who cannot resolve the boot up problem after upgrading to Sierra.

1. Shut down your Mac.
2. Press the power button to start up your Mac.
3. Immediately Hold down Command-S for single-user mode.
4. On the terminal window Type fsck –fy and press return
5. Type mount –uw and press return
6. Type touch /private/var/db/.AppleSetupDone and press return
7. Type exit and press return

Through Steps 1 to 3, you should have launched your Mac on a Single user mode.

In Step 3, the screen shows up the raw booting messages which show clearly what is running behind the scene.

Steps 4 to 7 will help check for file system consistency and remount the boot volume.

Regarding Step 6, what's point of creating empty file .AppleSetupDone?
Every time OS X boots, it checks for the existence of a file known as .AppleSetupDone. This empty file is created after the completion of Setup Assistant. It doesn't exist on a brand-new, out-of-the-box Mac, nor on one that has had a clean installation of OS X.
By removing this file, OS X will assume that Setup Assistant has never been run and will launch it as soon as OS X boots.
Setup Assistant is also run with root privileges, which is why it can create a new user account with administrator privileges without the need for any authorisation.

As I have gone through the wizards of Setup Assistant before bootup problem is encountered. I have not seen any wizard of Setup Assistant again.

After step 7, my MacBook booted into the logon screen which I usually see. I quickly login, and then restart it to see if things are working again. Finally, it booted up quickly and successfully to logon screen and let me login as usual.

As of writing, I can boot back into my Mac OS Sierra v10.12.2.

A fix to broken SSH key authenticated login after Mac Sierra Upgrade

For Mac OS, I feel that every major upgrade comes with some aftermaths which may cause short term migraine. The first thing to do could be looking up possible solutions from web searches in the hope that someone has figured out how to fix those post-upgrade problems. It reminds me that it would be safer to wait for a few months since every major OS upgrade has been released. The same truth holds for any other OS releases.

Problem encountered:
After the upgrade of Mac OS Sierra, I was unable to login to my linux box from my MacBook via SSH which was supposed to be using key authentication login without typing password.

Instead, I was asked for the passphrase for my key file like ~/.ssh/id_rsa. First of all, I found I forgot my passphrase. Actually, I have not been typing this passphrase for a while since I setup SSH key authentication on my MacBook for convenience.

The solution:
Someone suggests regenerating new key on local machine to resolve this. First thing first, you need to re-enable password authentication from the SSH server.

Another Mac user pointed out that the problem could be originated from the ssh-agent on Mac OS Sierra which is SSH v7.2 as of writing. A possible situation is that the ssh-agent does not automatically load passphrases on the keychain during startup.

To verify this, try the command:

$ ssh-add -l
The agent has no identities.

Clearly, there is no identity information stored in ssh-agent.

Let's store passphrase in your keychain again:

$ ssh-add -K <keyfile>

whereas <keyfile> could be the path like ~/.ssh/id_rsa, or whatever suits you

It will prompt for the passphrase and then will save them to the keychain. However, you might need to remind yourself the passphrase of that particular key file. If you have saved this in Keychain Access before, you can retrieve the passphrase under Keychains: login -> Category: Passwords in Keychain Access app.

You should be able to login again in the good old way of SSH key authentication, but it may not survive the next reboot for whatever reason since MacOS Sierra. Apple's Engineer states that this is expected and it is just re-aligned their behavior with the mainstream OpenSSH in this area. In other words, the stored passphrase for SSH keychain WILL NOT survive next reboot since MacOS Sierra.

You need to run the following command in Terminal again and again when you log back in MacOS Sierra:

$ ssh-add -A <keyfile>

It sounds like an immediate solution but lasts not long enough.

Taking one step forward, you can add a bash script to run SSH command with that particular identity file on your laptop:

#!/bin/bash
echo "Adding identities to SSH agent..."
ssh-add -A 2>/dev/null
echo "Logging in remote SSH server with specific identity file and port number..."
ssh -i <keyfile> -p <port> username@<remote_ssh_server_name_or_ip>

Ultimately, you can first log in your SSH box, re-enable password authentication on SSH server, regenerate a new RSA key on your laptop and then upload it to SSH box as permanent change. The key authentication will work with the newly generated identity file on Mac OS Sierra.

For details, check these out:
http://askubuntu.com/questions/46930/how-can-i-set-up-password-less-ssh-login
http://manpages.ubuntu.com/manpages/trusty/man1/ssh-copy-id.1.html
https://openradar.appspot.com/27348363