Prepares the system and then terminates all processes, usually ending with a hardware power-off. During preparation, all filesystem caches are flushed, and running processes are sent
SIGTERM followed by
Don't log the halt via syslog (i.e., mach_kernel: syncing disks...).
Don't flush filesystem caches. Should not be used indiscriminately.
The filesystem caches are flushed, but the system is otherwise halted ungracefully. Should not be used indiscriminately.