#Mac #OS hangs on blue screen just before #login - Mac-Forums.com
OS X will not boot if the boot volume lacks read access for ’everyone’.
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 /
Correct permissions are: drwxrwxr-t
The eighth character is critical. If it is not an r you can correct it as follows:
/sbin/mount -uw /
chmod 1775 /
Hopefully your Mac will now be OK and booting correctly. "