Boot failure looking for mDNSResponder

I was mistaken - it was not a permissions repair issue.

As far as I can tell (I will test further) it was caused by sharing the boot volume via Server Admin and then removing read access for 'everyone' (within Server Admin). In my opinion this is a serious bug - Server Admin settings should never be able to inhibit booting - preferably file sharing controlled by Server Admin should be totally independent of any local conventional OS X file sharing, or is this too much to expect?

Others finding this may be interested in my investigations and solution below:

OS X will not boot if the boot volume lacks read access for 'everyone'.

My investigations show that this can be caused by:

Tiger - Terminal (sudo chmod 770 /) - G4 with OS X 10.4.11

Leopard - Terminal (sudo chmod 770 /) and Finder Get Info - G4 with OS X 10.5.8

Snow Leopard Server - Disabling 'everyone' access to boot volume in Server Admin (bug?) - Xserve with OS X Server 10.6.2

Symptoms: Boot failure with indefinite (sometimes intermittent) spinning gear. This step is unnecessary but it provides another symptom of this issue - boot in Verbose Mode (cmd v at start-up) and look for the following repeated every few seconds; 'posix_spawnp("/usr/bin/mDNSResponder", ...): No such file or directory'.

To confirm that the cause is incorrect boot volume permissions start in Single User Mode (cmd s at start-up). Wait until all activity subsides and type:

ls -ld /

followed by the return key.

Correct permissions are: drwxrwxr-t

The eighth character is critical. If it is not an r you can correct it as follows:

Type:

/sbin/mount -uw /

followed by the return key.

Type:

chmod 1775 /

followed by the return key.

Type:

exit

followed by the return key.

Hopefully your Mac will now be OK and booting correctly.