mdworker: unable to talk to lsboxd

Too long without a crash already. Yesterday nothing interesting happened. Today no sign of anything crashing on my machine. Time to find something broken.
In my Console.app, a few messages repeat endlessly. I have noticed them before, but did not give it much attention as nothing seemed really broken. These are the messages:

May 14 15:28:41 Berik.local mdworker[88273]: Unable to talk to lsboxd
May 14 15:28:41 Berik.local sandboxd[88275] ([88274]): mdworker(88274) deny mach-lookup com.apple.ls.boxd
May 14 15:28:41 Berik kernel[0]: Sandbox: sandboxd(88275) deny mach-lookup com.apple.coresymbolicationd

These messages are related. Jay Barnes suggests to boot in safe mode to fix these warnings.
So, here we go.
There is an apple support page on how to boot in safe mode.
When I tried, the boot got stuck on 1/3rd on the progress bar. I waited for an hour, but the boot was obviously not going to happen.

Which brings me to this article about resolving failing safe mode boots. It turs out that I had some file system errors, and needed to boot to "Recovery" mode. After fixing the filesystem issues, and sending a bugreport to apple for the hanging safe boot (there should at least be some message displayed to the user),  the safe boot still hangs at 1/3rd of the progress bar.

Next will be to see the logs during the safe boot by changing the nvram: sudo nvram boot-args="-v -x"

This command will change the NVRam, memory that is not erased by rebooting and not erased by changing disk drives. The CNet article suggests to reset the NVRam after the safe boot was done.
The nvram command line utility can safe your current nvram to a file so you can restore it later.

To safe your current nvram: nvram -p > ~/nvram
To later restore the nvram: nvram -f ~/nvram

Before rebooting, I write down the keyboard shortcut to reset the nvram: Cmd-Opt-P-R These keys should be pressed while your machine is booting. The nvram will be reset when the screen becomes grey, then goes black. This is when you should release the keys and wait for the machine to boot normally again.

The debug output during the safe mode boot did not yield much. The last lines where:
** /dev/rdisk0s2
    Using cacheBlockSize=32K cacheTotalBlock=98304 cacheSize=3145728K.
** Root file system
    Executing fsck_hfs (version diskdev_cmds-557~393).
** Checking Journaled HFS Plus volume.
   The volume name is Mackintosh HD
** Checking extents overflow file.
** Checking catalog file.
AppleUSBMultitouchDriver::checkStatus - received Status Packet, Payload 2: device was reinitialised
** Checking multi-linked files.
** Checking catalog hierarchy.
** Checking extended attributes file.

The apple bug report was closed as "duplicate". Apple already knows that booting in safe mode can cause a system hang.